Forbid user to change file flags on quota files

Forbid user from changing file flags on quota files.  User has no bussiness
in playing with these flags when quota is on.  Furthermore there is a
remote possibility of deadlock due to a lock inversion between quota file's
i_mutex and transaction's start (i_mutex for quota file is locked only when
trasaction is started in quota operations) in ext3 and ext4.

Signed-off-by: Jan Kara <jack@suse.cz>
Cc: LIOU Payphone <lioupayphone@gmail.com>
Cc: <linux-ext4@vger.kernel.org>
Acked-by: Dave Kleikamp <shaggy@austin.ibm.com>
Cc: <reiserfs-dev@namesys.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/ext3/ioctl.c b/fs/ext3/ioctl.c
index 4a2a02c95bf9..023a070f55f1 100644
--- a/fs/ext3/ioctl.c
+++ b/fs/ext3/ioctl.c
@@ -51,6 +51,11 @@ int ext3_ioctl (struct inode * inode, struct file * filp, unsigned int cmd,
                         flags &= ~EXT3_DIRSYNC_FL;
 
                 mutex_lock(&inode->i_mutex);
+                /* Is it quota file? Do not allow user to mess with it */
+                if (IS_NOQUOTA(inode)) {
+                        mutex_unlock(&inode->i_mutex);
+                        return -EPERM;
+                }
                 oldflags = ei->i_flags;
 
                 /* The JOURNAL_DATA flag is modifiable only by root */