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* VFS: (Scripted) Convert S_ISLNK/DIR/REG(dentry->d_inode) to d_is_*(dentry)David Howells2015-02-22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Convert the following where appropriate: (1) S_ISLNK(dentry->d_inode) to d_is_symlink(dentry). (2) S_ISREG(dentry->d_inode) to d_is_reg(dentry). (3) S_ISDIR(dentry->d_inode) to d_is_dir(dentry). This is actually more complicated than it appears as some calls should be converted to d_can_lookup() instead. The difference is whether the directory in question is a real dir with a ->lookup op or whether it's a fake dir with a ->d_automount op. In some circumstances, we can subsume checks for dentry->d_inode not being NULL into this, provided we the code isn't in a filesystem that expects d_inode to be NULL if the dirent really *is* negative (ie. if we're going to use d_inode() rather than d_backing_inode() to get the inode pointer). Note that the dentry type field may be set to something other than DCACHE_MISS_TYPE when d_inode is NULL in the case of unionmount, where the VFS manages the fall-through from a negative dentry to a lower layer. In such a case, the dentry type of the negative union dentry is set to the same as the type of the lower dentry. However, if you know d_inode is not NULL at the call site, then you can use the d_is_xxx() functions even in a filesystem. There is one further complication: a 0,0 chardev dentry may be labelled DCACHE_WHITEOUT_TYPE rather than DCACHE_SPECIAL_TYPE. Strictly, this was intended for special directory entry types that don't have attached inodes. The following perl+coccinelle script was used: use strict; my @callers; open($fd, 'git grep -l \'S_IS[A-Z].*->d_inode\' |') || die "Can't grep for S_ISDIR and co. callers"; @callers = <$fd>; close($fd); unless (@callers) { print "No matches\n"; exit(0); } my @cocci = ( '@@', 'expression E;', '@@', '', '- S_ISLNK(E->d_inode->i_mode)', '+ d_is_symlink(E)', '', '@@', 'expression E;', '@@', '', '- S_ISDIR(E->d_inode->i_mode)', '+ d_is_dir(E)', '', '@@', 'expression E;', '@@', '', '- S_ISREG(E->d_inode->i_mode)', '+ d_is_reg(E)' ); my $coccifile = "tmp.sp.cocci"; open($fd, ">$coccifile") || die $coccifile; print($fd "$_\n") || die $coccifile foreach (@cocci); close($fd); foreach my $file (@callers) { chomp $file; print "Processing ", $file, "\n"; system("spatch", "--sp-file", $coccifile, $file, "--in-place", "--no-show-diff") == 0 || die "spatch failed"; } [AV: overlayfs parts skipped] Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* Merge branch 'for-linus' of ↵Linus Torvalds2015-02-17
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull misc VFS updates from Al Viro: "This cycle a lot of stuff sits on topical branches, so I'll be sending more or less one pull request per branch. This is the first pile; more to follow in a few. In this one are several misc commits from early in the cycle (before I went for separate branches), plus the rework of mntput/dput ordering on umount, switching to use of fs_pin instead of convoluted games in namespace_unlock()" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: switch the IO-triggering parts of umount to fs_pin new fs_pin killing logics allow attaching fs_pin to a group not associated with some superblock get rid of the second argument of acct_kill() take count and rcu_head out of fs_pin dcache: let the dentry count go down to zero without taking d_lock pull bumping refcount into ->kill() kill pin_put() mode_t whack-a-mole: chelsio file->f_path.dentry is pinned down for as long as the file is open... get rid of lustre_dump_dentry() gut proc_register() a bit kill d_validate() ncpfs: get rid of d_validate() nonsense selinuxfs: don't open-code d_genocide()
| * switch the IO-triggering parts of umount to fs_pinAl Viro2015-01-25
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | fs/namespace: convert devname allocation to kstrdup_constAndrzej Hajda2015-02-14
|/ | | | | | | | | | | | | | | | | | | | | VFS frequently performs duplication of strings located in read-only memory section. Replacing kstrdup by kstrdup_const allows to avoid such operations. Signed-off-by: Andrzej Hajda <a.hajda@samsung.com> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mike Turquette <mturquette@linaro.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Tejun Heo <tj@kernel.org> Cc: Greg KH <greg@kroah.com> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mnt: Fix a memory stomp in umountEric W. Biederman2014-12-18
| | | | | | | | | | | | | | | | | | | | | | | | | | | | While reviewing the code of umount_tree I realized that when we append to a preexisting unmounted list we do not change pprev of the former first item in the list. Which means later in namespace_unlock hlist_del_init(&mnt->mnt_hash) on the former first item of the list will stomp unmounted.first leaving it set to some random mount point which we are likely to free soon. This isn't likely to hit, but if it does I don't know how anyone could track it down. [ This happened because we don't have all the same operations for hlist's as we do for normal doubly-linked lists. In particular, list_splice() is easy on our standard doubly-linked lists, while hlist_splice() doesn't exist and needs both start/end entries of the hlist. And commit 38129a13e6e7 incorrectly open-coded that missing hlist_splice(). We should think about making these kinds of "mindless" conversions easier to get right by adding the missing hlist helpers - Linus ] Fixes: 38129a13e6e71f666e0468e99fdd932a687b4d7e switch mnt_hash to hlist Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Merge branch 'for-linus' of ↵Linus Torvalds2014-12-17
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace Pull user namespace related fixes from Eric Biederman: "As these are bug fixes almost all of thes changes are marked for backporting to stable. The first change (implicitly adding MNT_NODEV on remount) addresses a regression that was created when security issues with unprivileged remount were closed. I go on to update the remount test to make it easy to detect if this issue reoccurs. Then there are a handful of mount and umount related fixes. Then half of the changes deal with the a recently discovered design bug in the permission checks of gid_map. Unix since the beginning has allowed setting group permissions on files to less than the user and other permissions (aka ---rwx---rwx). As the unix permission checks stop as soon as a group matches, and setgroups allows setting groups that can not later be dropped, results in a situtation where it is possible to legitimately use a group to assign fewer privileges to a process. Which means dropping a group can increase a processes privileges. The fix I have adopted is that gid_map is now no longer writable without privilege unless the new file /proc/self/setgroups has been set to permanently disable setgroups. The bulk of user namespace using applications even the applications using applications using user namespaces without privilege remain unaffected by this change. Unfortunately this ix breaks a couple user space applications, that were relying on the problematic behavior (one of which was tools/selftests/mount/unprivileged-remount-test.c). To hopefully prevent needing a regression fix on top of my security fix I rounded folks who work with the container implementations mostly like to be affected and encouraged them to test the changes. > So far nothing broke on my libvirt-lxc test bed. :-) > Tested with openSUSE 13.2 and libvirt 1.2.9. > Tested-by: Richard Weinberger <richard@nod.at> > Tested on Fedora20 with libvirt 1.2.11, works fine. > Tested-by: Chen Hanxiao <chenhanxiao@cn.fujitsu.com> > Ok, thanks - yes, unprivileged lxc is working fine with your kernels. > Just to be sure I was testing the right thing I also tested using > my unprivileged nsexec testcases, and they failed on setgroup/setgid > as now expected, and succeeded there without your patches. > Tested-by: Serge Hallyn <serge.hallyn@ubuntu.com> > I tested this with Sandstorm. It breaks as is and it works if I add > the setgroups thing. > Tested-by: Andy Lutomirski <luto@amacapital.net> # breaks things as designed :(" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: userns: Unbreak the unprivileged remount tests userns; Correct the comment in map_write userns: Allow setting gid_maps without privilege when setgroups is disabled userns: Add a knob to disable setgroups on a per user namespace basis userns: Rename id_map_mutex to userns_state_mutex userns: Only allow the creator of the userns unprivileged mappings userns: Check euid no fsuid when establishing an unprivileged uid mapping userns: Don't allow unprivileged creation of gid mappings userns: Don't allow setgroups until a gid mapping has been setablished userns: Document what the invariant required for safe unprivileged mappings. groups: Consolidate the setgroups permission checks mnt: Clear mnt_expire during pivot_root mnt: Carefully set CL_UNPRIVILEGED in clone_mnt mnt: Move the clear of MNT_LOCKED from copy_tree to it's callers. umount: Do not allow unmounting rootfs. umount: Disallow unprivileged mount force mnt: Update unprivileged remount test mnt: Implicitly add MNT_NODEV on remount when it was implicitly added by mount
| * mnt: Clear mnt_expire during pivot_rootEric W. Biederman2014-12-02
| | | | | | | | | | | | | | | | | | | | | | When inspecting the pivot_root and the current mount expiry logic I realized that pivot_root fails to clear like mount move does. Add the missing line in case someone does the interesting feat of moving an expirable submount. This gives a strong guarantee that root of the filesystem tree will never expire. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * mnt: Carefully set CL_UNPRIVILEGED in clone_mntEric W. Biederman2014-12-02
| | | | | | | | | | | | old->mnt_expiry should be ignored unless CL_EXPIRE is set. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * mnt: Move the clear of MNT_LOCKED from copy_tree to it's callers.Eric W. Biederman2014-12-02
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Clear MNT_LOCKED in the callers of copy_tree except copy_mnt_ns, and collect_mounts. In copy_mnt_ns it is necessary to create an exact copy of a mount tree, so not clearing MNT_LOCKED is important. Similarly collect_mounts is used to take a snapshot of the mount tree for audit logging purposes and auditing using a faithful copy of the tree is important. This becomes particularly significant when we start setting MNT_LOCKED on rootfs to prevent it from being unmounted. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * umount: Do not allow unmounting rootfs.Eric W. Biederman2014-12-02
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Andrew Vagin <avagin@parallels.com> writes: > #define _GNU_SOURCE > #include <sys/types.h> > #include <sys/stat.h> > #include <fcntl.h> > #include <sched.h> > #include <unistd.h> > #include <sys/mount.h> > > int main(int argc, char **argv) > { > int fd; > > fd = open("/proc/self/ns/mnt", O_RDONLY); > if (fd < 0) > return 1; > while (1) { > if (umount2("/", MNT_DETACH) || > setns(fd, CLONE_NEWNS)) > break; > } > > return 0; > } > > root@ubuntu:/home/avagin# gcc -Wall nsenter.c -o nsenter > root@ubuntu:/home/avagin# strace ./nsenter > execve("./nsenter", ["./nsenter"], [/* 22 vars */]) = 0 > ... > open("/proc/self/ns/mnt", O_RDONLY) = 3 > umount("/", MNT_DETACH) = 0 > setns(3, 131072) = 0 > umount("/", MNT_DETACH > causes: > [ 260.548301] ------------[ cut here ]------------ > [ 260.550941] kernel BUG at /build/buildd/linux-3.13.0/fs/pnode.c:372! > [ 260.552068] invalid opcode: 0000 [#1] SMP > [ 260.552068] Modules linked in: xt_CHECKSUM iptable_mangle xt_tcpudp xt_addrtype xt_conntrack ipt_MASQUERADE iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack bridge stp llc dm_thin_pool dm_persistent_data dm_bufio dm_bio_prison iptable_filter ip_tables x_tables crct10dif_pclmul crc32_pclmul ghash_clmulni_intel binfmt_misc nfsd auth_rpcgss nfs_acl aesni_intel nfs lockd aes_x86_64 sunrpc fscache lrw gf128mul glue_helper ablk_helper cryptd serio_raw ppdev parport_pc lp parport btrfs xor raid6_pq libcrc32c psmouse floppy > [ 260.552068] CPU: 0 PID: 1723 Comm: nsenter Not tainted 3.13.0-30-generic #55-Ubuntu > [ 260.552068] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > [ 260.552068] task: ffff8800376097f0 ti: ffff880074824000 task.ti: ffff880074824000 > [ 260.552068] RIP: 0010:[<ffffffff811e9483>] [<ffffffff811e9483>] propagate_umount+0x123/0x130 > [ 260.552068] RSP: 0018:ffff880074825e98 EFLAGS: 00010246 > [ 260.552068] RAX: ffff88007c741140 RBX: 0000000000000002 RCX: ffff88007c741190 > [ 260.552068] RDX: ffff88007c741190 RSI: ffff880074825ec0 RDI: ffff880074825ec0 > [ 260.552068] RBP: ffff880074825eb0 R08: 00000000000172e0 R09: ffff88007fc172e0 > [ 260.552068] R10: ffffffff811cc642 R11: ffffea0001d59000 R12: ffff88007c741140 > [ 260.552068] R13: ffff88007c741140 R14: ffff88007c741140 R15: 0000000000000000 > [ 260.552068] FS: 00007fd5c7e41740(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000 > [ 260.552068] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 260.552068] CR2: 00007fd5c7968050 CR3: 0000000070124000 CR4: 00000000000406f0 > [ 260.552068] Stack: > [ 260.552068] 0000000000000002 0000000000000002 ffff88007c631000 ffff880074825ed8 > [ 260.552068] ffffffff811dcfac ffff88007c741140 0000000000000002 ffff88007c741160 > [ 260.552068] ffff880074825f38 ffffffff811dd12b ffffffff811cc642 0000000075640000 > [ 260.552068] Call Trace: > [ 260.552068] [<ffffffff811dcfac>] umount_tree+0x20c/0x260 > [ 260.552068] [<ffffffff811dd12b>] do_umount+0x12b/0x300 > [ 260.552068] [<ffffffff811cc642>] ? final_putname+0x22/0x50 > [ 260.552068] [<ffffffff811cc849>] ? putname+0x29/0x40 > [ 260.552068] [<ffffffff811dd88c>] SyS_umount+0xdc/0x100 > [ 260.552068] [<ffffffff8172aeff>] tracesys+0xe1/0xe6 > [ 260.552068] Code: 89 50 08 48 8b 50 08 48 89 02 49 89 45 08 e9 72 ff ff ff 0f 1f 44 00 00 4c 89 e6 4c 89 e7 e8 f5 f6 ff ff 48 89 c3 e9 39 ff ff ff <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 90 66 66 66 66 90 55 b8 01 > [ 260.552068] RIP [<ffffffff811e9483>] propagate_umount+0x123/0x130 > [ 260.552068] RSP <ffff880074825e98> > [ 260.611451] ---[ end trace 11c33d85f1d4c652 ]-- Which in practice is totally uninteresting. Only the global root user can do it, and it is just a stupid thing to do. However that is no excuse to allow a silly way to oops the kernel. We can avoid this silly problem by setting MNT_LOCKED on the rootfs mount point and thus avoid needing any special cases in the unmount code. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * umount: Disallow unprivileged mount forceEric W. Biederman2014-12-02
| | | | | | | | | | | | | | | | | | | | | | Forced unmount affects not just the mount namespace but the underlying superblock as well. Restrict forced unmount to the global root user for now. Otherwise it becomes possible a user in a less privileged mount namespace to force the shutdown of a superblock of a filesystem in a more privileged mount namespace, allowing a DOS attack on root. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * mnt: Implicitly add MNT_NODEV on remount when it was implicitly added by mountEric W. Biederman2014-12-02
| | | | | | | | | | | | | | | | | | | | | | | | | | Now that remount is properly enforcing the rule that you can't remove nodev at least sandstorm.io is breaking when performing a remount. It turns out that there is an easy intuitive solution implicitly add nodev on remount when nodev was implicitly added on mount. Tested-by: Cedric Bosdonnat <cbosdonnat@suse.com> Tested-by: Richard Weinberger <richard@nod.at> Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
* | take the targets of /proc/*/ns/* symlinks to separate fsAl Viro2014-12-10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | New pseudo-filesystem: nsfs. Targets of /proc/*/ns/* live there now. It's not mountable (not even registered, so it's not in /proc/filesystems, etc.). Files on it *are* bindable - we explicitly permit that in do_loopback(). This stuff lives in fs/nsfs.c now; proc_ns_fget() moved there as well. get_proc_ns() is a macro now (it's simply returning ->i_private; would have been an inline, if not for header ordering headache). proc_ns_inode() is an ex-parrot. The interface used in procfs is ns_get_path(path, task, ops) and ns_get_name(buf, size, task, ops). Dentries and inodes are never hashed; a non-counting reference to dentry is stashed in ns_common (removed by ->d_prune()) and reused by ns_get_path() if present. See ns_get_path()/ns_prune_dentry/nsfs_evict() for details of that mechanism. As the result, proc_ns_follow_link() has stopped poking in nd->path.mnt; it does nd_jump_link() on a consistent <vfsmount,dentry> pair it gets from ns_get_path(). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | bury struct proc_ns in fs/procAl Viro2014-12-04
| | | | | | | | | | | | | | | | | | | | a) make get_proc_ns() return a pointer to struct ns_common b) mirror ns_ops in dentry->d_fsdata of ns dentries, so that is_mnt_ns_file() could get away with fewer dereferences. That way struct proc_ns becomes invisible outside of fs/proc/*.c Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | copy address of proc_ns_ops into ns_commonAl Viro2014-12-04
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | new helpers: ns_alloc_inum/ns_free_inumAl Viro2014-12-04
| | | | | | | | | | | | take struct ns_common *, for now simply wrappers around proc_{alloc,free}_inum() Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | make proc_ns_operations work with struct ns_common * instead of void *Al Viro2014-12-04
| | | | | | | | | | | | | | We can do that now. And kill ->inum(), while we are at it - all instances are identical. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | make mntns ->get()/->put()/->install()/->inum() work with &mnt_ns->nsAl Viro2014-12-04
| | | | | | | | | | Acked-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | common object embedded into various struct ....nsAl Viro2014-12-04
|/ | | | | | | for now - just move corresponding ->proc_inum instances over there Acked-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* vfs: introduce clone_private_mount()Miklos Szeredi2014-10-23
| | | | | | | Overlayfs needs a private clone of the mount, so create a function for this and export to modules. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
* Merge branch 'CVE-2014-7970' of ↵Linus Torvalds2014-10-15
|\ | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux Pull pivot_root() fix from Andy Lutomirski. Prevent a leak of unreachable mounts. * 'CVE-2014-7970' of git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux: mnt: Prevent pivot_root from creating a loop in the mount tree
| * mnt: Prevent pivot_root from creating a loop in the mount treeEric W. Biederman2014-10-14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Andy Lutomirski recently demonstrated that when chroot is used to set the root path below the path for the new ``root'' passed to pivot_root the pivot_root system call succeeds and leaks mounts. In examining the code I see that starting with a new root that is below the current root in the mount tree will result in a loop in the mount tree after the mounts are detached and then reattached to one another. Resulting in all kinds of ugliness including a leak of that mounts involved in the leak of the mount loop. Prevent this problem by ensuring that the new mount is reachable from the current root of the mount tree. [Added stable cc. Fixes CVE-2014-7970. --Andy] Cc: stable@vger.kernel.org Reported-by: Andy Lutomirski <luto@amacapital.net> Reviewed-by: Andy Lutomirski <luto@amacapital.net> Link: http://lkml.kernel.org/r/87bnpmihks.fsf@x220.int.ebiederm.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
* | Merge branch 'CVE-2014-7975' of ↵Linus Torvalds2014-10-14
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux Pull do_umount fix from Andy Lutomirski: "This fix really ought to be safe. Inside a mountns owned by a non-root user namespace, the namespace root almost always has MNT_LOCKED set (if it doesn't, then there's a bug, because rootfs could be exposed). In that case, calling umount on "/" will return -EINVAL with or without this patch. Outside a userns, this patch will have no effect. may_mount, required by umount, already checks ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN) so an additional capable(CAP_SYS_ADMIN) check will have no effect. That leaves anything that calls umount on "/" in a non-root userns while chrooted. This is the case that is currently broken (it remounts ro, which shouldn't be allowed) and that my patch changes to -EPERM. If anything relies on *that*, I'd be surprised" * 'CVE-2014-7975' of git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux: fs: Add a missing permission check to do_umount
| * | fs: Add a missing permission check to do_umountAndy Lutomirski2014-10-08
| |/ | | | | | | | | | | | | | | | | Accessing do_remount_sb should require global CAP_SYS_ADMIN, but only one of the two call sites was appropriately protected. Fixes CVE-2014-7975. Signed-off-by: Andy Lutomirski <luto@amacapital.net>
* | vfs: move getname() from callers to do_mount()Seunghun Lee2014-10-09
| | | | | | | | | | | | | | | | | | It would make more sense to pass char __user * instead of char * in callers of do_mount() and do getname() inside do_mount(). Suggested-by: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Seunghun Lee <waydi1@gmail.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | fs: namespace: suppress 'may be used uninitialized' warningsTim Gardner2014-10-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The gcc version 4.9.1 compiler complains Even though it isn't possible for these variables to not get initialized before they are used. fs/namespace.c: In function ‘SyS_mount’: fs/namespace.c:2720:8: warning: ‘kernel_dev’ may be used uninitialized in this function [-Wmaybe-uninitialized] ret = do_mount(kernel_dev, kernel_dir->name, kernel_type, flags, ^ fs/namespace.c:2699:8: note: ‘kernel_dev’ was declared here char *kernel_dev; ^ fs/namespace.c:2720:8: warning: ‘kernel_type’ may be used uninitialized in this function [-Wmaybe-uninitialized] ret = do_mount(kernel_dev, kernel_dir->name, kernel_type, flags, ^ fs/namespace.c:2697:8: note: ‘kernel_type’ was declared here char *kernel_type; ^ Fix the warnings by simplifying copy_mount_string() as suggested by Al Viro. Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Tim Gardner <tim.gardner@canonical.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | vfs: Add a function to lazily unmount all mounts from any dentry.Eric W. Biederman2014-10-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The new function detach_mounts comes in two pieces. The first piece is a static inline test of d_mounpoint that returns immediately without taking any locks if d_mounpoint is not set. In the common case when mountpoints are absent this allows the vfs to continue running with it's same cacheline foot print. The second piece of detach_mounts __detach_mounts actually does the work and it assumes that a mountpoint is present so it is slow and takes namespace_sem for write, and then locks the mount hash (aka mount_lock) after a struct mountpoint has been found. With those two locks held each entry on the list of mounts on a mountpoint is selected and lazily unmounted until all of the mount have been lazily unmounted. v7: Wrote a proper change description and removed the changelog documenting deleted wrong turns. Signed-off-by: Eric W. Biederman <ebiederman@twitter.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | vfs: factor out lookup_mountpoint from new_mountpointEric W. Biederman2014-10-09
| | | | | | | | | | | | | | | | | | | | | | I am shortly going to add a new user of struct mountpoint that needs to look up existing entries but does not want to create a struct mountpoint if one does not exist. Therefore to keep the code simple and easy to read split out lookup_mountpoint from new_mountpoint. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | vfs: Keep a list of mounts on a mount pointEric W. Biederman2014-10-09
| | | | | | | | | | | | | | | | | | | | | | To spot any possible problems call BUG if a mountpoint is put when it's list of mounts is not empty. AV: use hlist instead of list_head Reviewed-by: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: Eric W. Biederman <ebiederman@twitter.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | vfs: Don't allow overwriting mounts in the current mount namespaceEric W. Biederman2014-10-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In preparation for allowing mountpoints to be renamed and unlinked in remote filesystems and in other mount namespaces test if on a dentry there is a mount in the local mount namespace before allowing it to be renamed or unlinked. The primary motivation here are old versions of fusermount unmount which is not safe if the a path can be renamed or unlinked while it is verifying the mount is safe to unmount. More recent versions are simpler and safer by simply using UMOUNT_NOFOLLOW when unmounting a mount in a directory owned by an arbitrary user. Miklos Szeredi <miklos@szeredi.hu> reports this is approach is good enough to remove concerns about new kernels mixed with old versions of fusermount. A secondary motivation for restrictions here is that it removing empty directories that have non-empty mount points on them appears to violate the rule that rmdir can not remove empty directories. As Linus Torvalds pointed out this is useful for programs (like git) that test if a directory is empty with rmdir. Therefore this patch arranges to enforce the existing mount point semantics for local mount namespace. v2: Rewrote the test to be a drop in replacement for d_mountpoint v3: Use bool instead of int as the return type of is_local_mountpoint Reviewed-by: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | delayed mntputAl Viro2014-10-09
|/ | | | | | | | | | | | | | | | On final mntput() we want fs shutdown to happen before return to userland; however, the only case where we want it happen right there (i.e. where task_work_add won't do) is MNT_INTERNAL victim. Those have to be fully synchronous - failure halfway through module init might count on having vfsmount killed right there. Fortunately, final mntput on MNT_INTERNAL vfsmounts happens on shallow stack. So we handle those synchronously and do an analog of delayed fput logics for everything else. As the result, we are guaranteed that fs shutdown will always happen on shallow stack. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* fix EBUSY on umount() from MNT_SHRINKABLEAl Viro2014-08-30
| | | | | | | | | | | | | | | | We need the parents of victims alive until namespace_unlock() gets to dput() of the (ex-)mountpoints. However, that screws up the "is it busy" checks in case when we have shrinkable mounts that need to be killed. Solution: go ahead and decrement refcounts of parents right in umount_tree(), increment them again just before dropping rwsem in namespace_unlock() (and let the loop in the end of namespace_unlock() finally drop those references for good, as we do now). Parents can't get freed until we drop rwsem - at least one reference is kept until then, both in case when parent is among the victims and when it is not. So they'll still be around when we get to namespace_unlock(). Cc: stable@vger.kernel.org # 3.12+ Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* get rid of propagate_umount() mistakenly treating slaves as busy.Al Viro2014-08-30
| | | | | | | | | The check in __propagate_umount() ("has somebody explicitly mounted something on that slave?") is done *before* taking the already doomed victims out of the child lists. Cc: stable@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* Merge branch 'for-linus' of ↵Linus Torvalds2014-08-11
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull vfs updates from Al Viro: "Stuff in here: - acct.c fixes and general rework of mnt_pin mechanism. That allows to go for delayed-mntput stuff, which will permit mntput() on deep stack without worrying about stack overflows - fs shutdown will happen on shallow stack. IOW, we can do Eric's umount-on-rmdir series without introducing tons of stack overflows on new mntput() call chains it introduces. - Bruce's d_splice_alias() patches - more Miklos' rename() stuff. - a couple of regression fixes (stable fodder, in the end of branch) and a fix for API idiocy in iov_iter.c. There definitely will be another pile, maybe even two. I'd like to get Eric's series in this time, but even if we miss it, it'll go right in the beginning of for-next in the next cycle - the tricky part of prereqs is in this pile" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (40 commits) fix copy_tree() regression __generic_file_write_iter(): fix handling of sync error after DIO switch iov_iter_get_pages() to passing maximal number of pages fs: mark __d_obtain_alias static dcache: d_splice_alias should detect loops exportfs: update Exporting documentation dcache: d_find_alias needn't recheck IS_ROOT && DCACHE_DISCONNECTED dcache: remove unused d_find_alias parameter dcache: d_obtain_alias callers don't all want DISCONNECTED dcache: d_splice_alias should ignore DCACHE_DISCONNECTED dcache: d_splice_alias mustn't create directory aliases dcache: close d_move race in d_splice_alias dcache: move d_splice_alias namei: trivial fix to vfs_rename_dir comment VFS: allow ->d_manage() to declare -EISDIR in rcu_walk mode. cifs: support RENAME_NOREPLACE hostfs: support rename flags shmem: support RENAME_EXCHANGE shmem: support RENAME_NOREPLACE btrfs: add RENAME_NOREPLACE ...
| * fix copy_tree() regressionAl Viro2014-08-11
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Since 3.14 we had copy_tree() get the shadowing wrong - if we had one vfsmount shadowing another (i.e. if A is a slave of B, C is mounted on A/foo, then D got mounted on B/foo creating D' on A/foo shadowed by C), copy_tree() of A would make a copy of D' shadow the the copy of C, not the other way around. It's easy to fix, fortunately - just make sure that mount follows the one that shadows it in mnt_child as well as in mnt_hash, and when copy_tree() decides to attach a new mount, check if the last child it has added to the same parent should be shadowing the new one. And if it should, just use the same logics commit_tree() has - put the new mount into the hash and children lists right after the one that should shadow it. Cc: stable@vger.kernel.org [3.14 and later] Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * death to mnt_pinnedAl Viro2014-08-07
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Rather than playing silly buggers with vfsmount refcounts, just have acct_on() ask fs/namespace.c for internal clone of file->f_path.mnt and replace it with said clone. Then attach the pin to original vfsmount. Voila - the clone will be alive until the file gets closed, making sure that underlying superblock remains active, etc., and we can drop the original vfsmount, so that it's not kept busy. If the file lives until the final mntput of the original vfsmount, we'll notice that there's an fs_pin (one in bsd_acct_struct that holds that file) and mnt_pin_kill() will take it out. Since ->kill() is synchronous, we won't proceed past that point until these files are closed (and private clones of our vfsmount are gone), so we get the same ordering warranties we used to get. mnt_pin()/mnt_unpin()/->mnt_pinned is gone now, and good riddance - it never became usable outside of kernel/acct.c (and racy wrt umount even there). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * make fs/{namespace,super}.c forget about acct.hAl Viro2014-08-07
| | | | | | | | | | | | | | These externs belong in fs/internal.h. Rename (they are not acct-specific anymore) and move them over there. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * acct: get rid of acct_listAl Viro2014-08-07
| | | | | | | | | | | | | | | | Put these suckers on per-vfsmount and per-superblock lists instead. Note: right now it's still acct_lock for everything, but that's going to change. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | Merge branch 'for-linus' of ↵Linus Torvalds2014-08-09
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace Pull namespace updates from Eric Biederman: "This is a bunch of small changes built against 3.16-rc6. The most significant change for users is the first patch which makes setns drmatically faster by removing unneded rcu handling. The next chunk of changes are so that "mount -o remount,.." will not allow the user namespace root to drop flags on a mount set by the system wide root. Aks this forces read-only mounts to stay read-only, no-dev mounts to stay no-dev, no-suid mounts to stay no-suid, no-exec mounts to stay no exec and it prevents unprivileged users from messing with a mounts atime settings. I have included my test case as the last patch in this series so people performing backports can verify this change works correctly. The next change fixes a bug in NFS that was discovered while auditing nsproxy users for the first optimization. Today you can oops the kernel by reading /proc/fs/nfsfs/{servers,volumes} if you are clever with pid namespaces. I rebased and fixed the build of the !CONFIG_NFS_FS case yesterday when a build bot caught my typo. Given that no one to my knowledge bases anything on my tree fixing the typo in place seems more responsible that requiring a typo-fix to be backported as well. The last change is a small semantic cleanup introducing /proc/thread-self and pointing /proc/mounts and /proc/net at it. This prevents several kinds of problemantic corner cases. It is a user-visible change so it has a minute chance of causing regressions so the change to /proc/mounts and /proc/net are individual one line commits that can be trivially reverted. Unfortunately I lost and could not find the email of the original reporter so he is not credited. From at least one perspective this change to /proc/net is a refgression fix to allow pthread /proc/net uses that were broken by the introduction of the network namespace" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: proc: Point /proc/mounts at /proc/thread-self/mounts instead of /proc/self/mounts proc: Point /proc/net at /proc/thread-self/net instead of /proc/self/net proc: Implement /proc/thread-self to point at the directory of the current thread proc: Have net show up under /proc/<tgid>/task/<tid> NFS: Fix /proc/fs/nfsfs/servers and /proc/fs/nfsfs/volumes mnt: Add tests for unprivileged remount cases that have found to be faulty mnt: Change the default remount atime from relatime to the existing value mnt: Correct permission checks in do_remount mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount mnt: Only change user settable mount flags in remount namespaces: Use task_lock and not rcu to protect nsproxy
| * | mnt: Change the default remount atime from relatime to the existing valueEric W. Biederman2014-07-31
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Since March 2009 the kernel has treated the state that if no MS_..ATIME flags are passed then the kernel defaults to relatime. Defaulting to relatime instead of the existing atime state during a remount is silly, and causes problems in practice for people who don't specify any MS_...ATIME flags and to get the default filesystem atime setting. Those users may encounter a permission error because the default atime setting does not work. A default that does not work and causes permission problems is ridiculous, so preserve the existing value to have a default atime setting that is always guaranteed to work. Using the default atime setting in this way is particularly interesting for applications built to run in restricted userspace environments without /proc mounted, as the existing atime mount options of a filesystem can not be read from /proc/mounts. In practice this fixes user space that uses the default atime setting on remount that are broken by the permission checks keeping less privileged users from changing more privileged users atime settings. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * | mnt: Correct permission checks in do_remountEric W. Biederman2014-07-31
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | While invesgiating the issue where in "mount --bind -oremount,ro ..." would result in later "mount --bind -oremount,rw" succeeding even if the mount started off locked I realized that there are several additional mount flags that should be locked and are not. In particular MNT_NOSUID, MNT_NODEV, MNT_NOEXEC, and the atime flags in addition to MNT_READONLY should all be locked. These flags are all per superblock, can all be changed with MS_BIND, and should not be changable if set by a more privileged user. The following additions to the current logic are added in this patch. - nosuid may not be clearable by a less privileged user. - nodev may not be clearable by a less privielged user. - noexec may not be clearable by a less privileged user. - atime flags may not be changeable by a less privileged user. The logic with atime is that always setting atime on access is a global policy and backup software and auditing software could break if atime bits are not updated (when they are configured to be updated), and serious performance degradation could result (DOS attack) if atime updates happen when they have been explicitly disabled. Therefore an unprivileged user should not be able to mess with the atime bits set by a more privileged user. The additional restrictions are implemented with the addition of MNT_LOCK_NOSUID, MNT_LOCK_NODEV, MNT_LOCK_NOEXEC, and MNT_LOCK_ATIME mnt flags. Taken together these changes and the fixes for MNT_LOCK_READONLY should make it safe for an unprivileged user to create a user namespace and to call "mount --bind -o remount,... ..." without the danger of mount flags being changed maliciously. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * | mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remountEric W. Biederman2014-07-31
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There are no races as locked mount flags are guaranteed to never change. Moving the test into do_remount makes it more visible, and ensures all filesystem remounts pass the MNT_LOCK_READONLY permission check. This second case is not an issue today as filesystem remounts are guarded by capable(CAP_DAC_ADMIN) and thus will always fail in less privileged mount namespaces, but it could become an issue in the future. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * | mnt: Only change user settable mount flags in remountEric W. Biederman2014-07-31
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Kenton Varda <kenton@sandstorm.io> discovered that by remounting a read-only bind mount read-only in a user namespace the MNT_LOCK_READONLY bit would be cleared, allowing an unprivileged user to the remount a read-only mount read-write. Correct this by replacing the mask of mount flags to preserve with a mask of mount flags that may be changed, and preserve all others. This ensures that any future bugs with this mask and remount will fail in an easy to detect way where new mount flags simply won't change. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
| * | namespaces: Use task_lock and not rcu to protect nsproxyEric W. Biederman2014-07-29
| |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The synchronous syncrhonize_rcu in switch_task_namespaces makes setns a sufficiently expensive system call that people have complained. Upon inspect nsproxy no longer needs rcu protection for remote reads. remote reads are rare. So optimize for same process reads and write by switching using rask_lock instead. This yields a simpler to understand lock, and a faster setns system call. In particular this fixes a performance regression observed by Rafael David Tinoco <rafael.tinoco@canonical.com>. This is effectively a revert of Pavel Emelyanov's commit cf7b708c8d1d7a27736771bcf4c457b332b0f818 Make access to task's nsproxy lighter from 2007. The race this originialy fixed no longer exists as do_notify_parent uses task_active_pid_ns(parent) instead of parent->nsproxy. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
* / list: fix order of arguments for hlist_add_after(_rcu)Ken Helias2014-08-06
|/ | | | | | | | | | | | | | | | | | | All other add functions for lists have the new item as first argument and the position where it is added as second argument. This was changed for no good reason in this function and makes using it unnecessary confusing. The name was changed to hlist_add_behind() to cause unconverted code to generate a compile error instead of using the wrong parameter order. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Ken Helias <kenhelias@firemail.de> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com> [intel driver bits] Cc: Hugh Dickins <hughd@google.com> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* VFS: Make delayed_free() call free_vfsmnt()David Howells2014-04-01
| | | | | | | | | Make delayed_free() call free_vfsmnt() so that we don't have two functions doing the same job. This requires the calls to mnt_free_id() in free_vfsmnt() to be moved into the callers of that function. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* mark struct file that had write access grabbed by open()Al Viro2014-04-01
| | | | | | | | | new flag in ->f_mode - FMODE_WRITER. Set by do_dentry_open() in case when it has grabbed write access, checked by __fput() to decide whether it wants to drop the sucker. Allows to stop bothering with mnt_clone_write() in alloc_file(), along with fewer special_file() checks. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* reduce m_start() cost...Al Viro2014-04-01
| | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* smarter propagate_mnt()Al Viro2014-04-01
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The current mainline has copies propagated to *all* nodes, then tears down the copies we made for nodes that do not contain counterparts of the desired mountpoint. That sets the right propagation graph for the copies (at teardown time we move the slaves of removed node to a surviving peer or directly to master), but we end up paying a fairly steep price in useless allocations. It's fairly easy to create a situation where N calls of mount(2) create exactly N bindings, with O(N^2) vfsmounts allocated and freed in process. Fortunately, it is possible to avoid those allocations/freeings. The trick is to create copies in the right order and find which one would've eventually become a master with the current algorithm. It turns out to be possible in O(nodes getting propagation) time and with no extra allocations at all. One part is that we need to make sure that eventual master will be created before its slaves, so we need to walk the propagation tree in a different order - by peer groups. And iterate through the peers before dealing with the next group. Another thing is finding the (earlier) copy that will be a master of one we are about to create; to do that we are (temporary) marking the masters of mountpoints we are attaching the copies to. Either we are in a peer of the last mountpoint we'd dealt with, or we have the following situation: we are attaching to mountpoint M, the last copy S_0 had been attached to M_0 and there are sequences S_0...S_n, M_0...M_n such that S_{i+1} is a master of S_{i}, S_{i} mounted on M{i} and we need to create a slave of the first S_{k} such that M is getting propagation from M_{k}. It means that the master of M_{k} will be among the sequence of masters of M. On the other hand, the nearest marked node in that sequence will either be the master of M_{k} or the master of M_{k-1} (the latter - in the case if M_{k-1} is a slave of something M gets propagation from, but in a wrong peer group). So we go through the sequence of masters of M until we find a marked one (P). Let N be the one before it. Then we go through the sequence of masters of S_0 until we find one (say, S) mounted on a node D that has P as master and check if D is a peer of N. If it is, S will be the master of new copy, if not - the master of S will be. That's it for the hard part; the rest is fairly simple. Iterator is in next_group(), handling of one prospective mountpoint is propagate_one(). It seems to survive all tests and gives a noticably better performance than the current mainline for setups that are seriously using shared subtrees. Cc: stable@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* switch mnt_hash to hlistAl Viro2014-03-30
| | | | | | | | | | | | | fixes RCU bug - walking through hlist is safe in face of element moves, since it's self-terminating. Cyclic lists are not - if we end up jumping to another hash chain, we'll loop infinitely without ever hitting the original list head. [fix for dumb braino folded] Spotted by: Max Kellermann <mk@cm4all.com> Cc: stable@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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