more conservative S_NOSEC handling

Caching "we have already removed suid/caps" was overenthusiastic as merged.
On network filesystems we might have had suid/caps set on another client,
silently picked by this client on revalidate, all of that *without* clearing
the S_NOSEC flag.

AFAICS, the only reasonably sane way to deal with that is
	* new superblock flag; unless set, S_NOSEC is not going to be set.
	* local block filesystems set it in their ->mount() (more accurately,
mount_bdev() does, so does btrfs ->mount(), users of mount_bdev() other than
local block ones clear it)
	* if any network filesystem (or a cluster one) wants to use S_NOSEC,
it'll need to set MS_NOSEC in sb->s_flags *AND* take care to clear S_NOSEC when
inode attribute changes are picked from other clients.

It's not an earth-shattering hole (anybody that can set suid on another client
will almost certainly be able to write to the file before doing that anyway),
but it's a bug that needs fixing.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 9b2e7e5bc3ef..d158b672a2d2 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -819,7 +819,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
         } else {
                 char b[BDEVNAME_SIZE];
 
-                s->s_flags = flags;
+                s->s_flags = flags | MS_NOSEC;
                 strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
                 error = btrfs_fill_super(s, fs_devices, data,
                                          flags & MS_SILENT ? 1 : 0);