Implement file posix capabilities

Implement file posix capabilities.  This allows programs to be given a
subset of root's powers regardless of who runs them, without having to use
setuid and giving the binary all of root's powers.

This version works with Kaigai Kohei's userspace tools, found at
http://www.kaigai.gr.jp/index.php.  For more information on how to use this
patch, Chris Friedhoff has posted a nice page at
http://www.friedhoff.org/fscaps.html.

Changelog:
	Nov 27:
	Incorporate fixes from Andrew Morton
	(security-introduce-file-caps-tweaks and
	security-introduce-file-caps-warning-fix)
	Fix Kconfig dependency.
	Fix change signaling behavior when file caps are not compiled in.

	Nov 13:
	Integrate comments from Alexey: Remove CONFIG_ ifdef from
	capability.h, and use %zd for printing a size_t.

	Nov 13:
	Fix endianness warnings by sparse as suggested by Alexey
	Dobriyan.

	Nov 09:
	Address warnings of unused variables at cap_bprm_set_security
	when file capabilities are disabled, and simultaneously clean
	up the code a little, by pulling the new code into a helper
	function.

	Nov 08:
	For pointers to required userspace tools and how to use
	them, see http://www.friedhoff.org/fscaps.html.

	Nov 07:
	Fix the calculation of the highest bit checked in
	check_cap_sanity().

	Nov 07:
	Allow file caps to be enabled without CONFIG_SECURITY, since
	capabilities are the default.
	Hook cap_task_setscheduler when !CONFIG_SECURITY.
	Move capable(TASK_KILL) to end of cap_task_kill to reduce
	audit messages.

	Nov 05:
	Add secondary calls in selinux/hooks.c to task_setioprio and
	task_setscheduler so that selinux and capabilities with file
	cap support can be stacked.

	Sep 05:
	As Seth Arnold points out, uid checks are out of place
	for capability code.

	Sep 01:
	Define task_setscheduler, task_setioprio, cap_task_kill, and
	task_setnice to make sure a user cannot affect a process in which
	they called a program with some fscaps.

	One remaining question is the note under task_setscheduler: are we
	ok with CAP_SYS_NICE being sufficient to confine a process to a
	cpuset?

	It is a semantic change, as without fsccaps, attach_task doesn't
	allow CAP_SYS_NICE to override the uid equivalence check.  But since
	it uses security_task_setscheduler, which elsewhere is used where
	CAP_SYS_NICE can be used to override the uid equivalence check,
	fixing it might be tough.

	     task_setscheduler
		 note: this also controls cpuset:attach_task.  Are we ok with
		     CAP_SYS_NICE being used to confine to a cpuset?
	     task_setioprio
	     task_setnice
		 sys_setpriority uses this (through set_one_prio) for another
		 process.  Need same checks as setrlimit

	Aug 21:
	Updated secureexec implementation to reflect the fact that
	euid and uid might be the same and nonzero, but the process
	might still have elevated caps.

	Aug 15:
	Handle endianness of xattrs.
	Enforce capability version match between kernel and disk.
	Enforce that no bits beyond the known max capability are
	set, else return -EPERM.
	With this extra processing, it may be worth reconsidering
	doing all the work at bprm_set_security rather than
	d_instantiate.

	Aug 10:
	Always call getxattr at bprm_set_security, rather than
	caching it at d_instantiate.

[morgan@kernel.org: file-caps clean up for linux/capability.h]
[bunk@kernel.org: unexport cap_inode_killpriv]
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Andrew Morgan <morgan@kernel.org>
Signed-off-by: Andrew Morgan <morgan@kernel.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 22 insertions, 7 deletions

diff --git a/fs/attr.c b/fs/attr.c
index f8dfc2269d85..ae58bd3f875f 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -116,6 +116,15 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
                 attr->ia_atime = now;
         if (!(ia_valid & ATTR_MTIME_SET))
                 attr->ia_mtime = now;
+        if (ia_valid & ATTR_KILL_PRIV) {
+                attr->ia_valid &= ~ATTR_KILL_PRIV;
+                ia_valid &= ~ATTR_KILL_PRIV;
+                error = security_inode_need_killpriv(dentry);
+                if (error > 0)
+                        error = security_inode_killpriv(dentry);
+                if (error)
+                        return error;
+        }
         if (ia_valid & ATTR_KILL_SUID) {
                 attr->ia_valid &= ~ATTR_KILL_SUID;
                 if (mode & S_ISUID) {
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 1d72f993b66e..819545d21670 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -368,7 +368,7 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
 
         /* Revoke setuid/setgid bit on chown/chgrp */
         if ((iap->ia_valid & ATTR_UID) && iap->ia_uid != inode->i_uid)
-                iap->ia_valid |= ATTR_KILL_SUID;
+                iap->ia_valid |= ATTR_KILL_SUID | ATTR_KILL_PRIV;
         if ((iap->ia_valid & ATTR_GID) && iap->ia_gid != inode->i_gid)
                 iap->ia_valid |= ATTR_KILL_SGID;
 
@@ -937,7 +937,7 @@ out:
 static void kill_suid(struct dentry *dentry)
 {
         struct iattr    ia;
-        ia.ia_valid = ATTR_KILL_SUID | ATTR_KILL_SGID;
+        ia.ia_valid = ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
 
         mutex_lock(&dentry->d_inode->i_mutex);
         notify_change(dentry, &ia);
diff --git a/fs/open.c b/fs/open.c
index cdbb94a9efc2..75385144df7d 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -658,7 +658,8 @@ static int chown_common(struct dentry * dentry, uid_t user, gid_t group)
                 newattrs.ia_gid = group;
         }
         if (!S_ISDIR(inode->i_mode))
-                newattrs.ia_valid |= ATTR_KILL_SUID|ATTR_KILL_SGID;
+                newattrs.ia_valid |=
+                        ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
         mutex_lock(&inode->i_mutex);
         error = notify_change(dentry, &newattrs);
         mutex_unlock(&inode->i_mutex);
diff --git a/fs/splice.c b/fs/splice.c
index 59a941d404d9..6bdcb6107bc3 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -824,13 +824,18 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 {
         struct address_space *mapping = out->f_mapping;
         struct inode *inode = mapping->host;
+        int killsuid, killpriv;
         ssize_t ret;
-        int err;
+        int err = 0;
 
-        err = should_remove_suid(out->f_path.dentry);
-        if (unlikely(err)) {
+        killpriv = security_inode_need_killpriv(out->f_path.dentry);
+        killsuid = should_remove_suid(out->f_path.dentry);
+        if (unlikely(killsuid || killpriv)) {
                 mutex_lock(&inode->i_mutex);
-                err = __remove_suid(out->f_path.dentry, err);
+                if (killpriv)
+                        err = security_inode_killpriv(out->f_path.dentry);
+                if (!err && killsuid)
+                        err = __remove_suid(out->f_path.dentry, killsuid);
                 mutex_unlock(&inode->i_mutex);
                 if (err)
                         return err;