Re: [PATCH v4 6/7] xfs: check that eofblocks ioctl caller can write matched inodes

Dave Chinner
2013-07-19T06:02:32Z

On Wed, Jul 17, 2013 at 11:47:46AM -0400, Dwight Engen wrote:
> Signed-off-by: Dwight Engen <dwight.engen@oracle.com>

What's the reason for this patch?

> ---
> fs/xfs/xfs_fs.h | 1 +
> fs/xfs/xfs_icache.c | 4 ++++
> fs/xfs/xfs_ioctl.c | 2 ++
> 3 files changed, 7 insertions(+)
>
> diff --git a/fs/xfs/xfs_fs.h b/fs/xfs/xfs_fs.h
> index 7eb4a5e..aee4b12 100644
> --- a/fs/xfs/xfs_fs.h
> +++ b/fs/xfs/xfs_fs.h
> @@ -361,6 +361,7 @@ struct xfs_fs_eofblocks {
> #define XFS_EOF_FLAGS_GID (1 << 2) /* filter by gid */
> #define XFS_EOF_FLAGS_PRID (1 << 3) /* filter by project id */
> #define XFS_EOF_FLAGS_MINFILESIZE (1 << 4) /* filter by min file size */
> +#define XFS_EOF_FLAGS_PERM_CHECK (1 << 5) /* check can write inode */
> #define XFS_EOF_FLAGS_VALID \
> (XFS_EOF_FLAGS_SYNC | \
> XFS_EOF_FLAGS_UID | \
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index d873ab9e..728283a 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -1247,6 +1247,10 @@ xfs_inode_free_eofblocks(
> if (!xfs_inode_match_id(ip, eofb))
> return 0;
>
> + if (eofb->eof_flags & XFS_EOF_FLAGS_PERM_CHECK &&
> + inode_permission(VFS_I(ip), MAY_WRITE))
> + return 0;

This assumes we are walking fully instantiated VFS inodes. That's
not necessarily true - we may be walking inodes that have already
been dropped from the VFS and are waiting for background reclaim to
clean them up. I suspect that this doesn't need to be done - we
normally stop background modification processes like this when we
convert the filesystem to read-only. I suspect the eof-blocks scan
code is missing that, and so it can potentially run on a RO
filesystem. That needs fixing similar to the way we stop and start
the periodic log work...

Also, gcc should throw warnings on that code (strange, it didn't
here on gcc-4.7) as it needs more parenthesis. i.e

if ((eofb->eof_flags & XFS_EOF_FLAGS_PERM_CHECK) &&

> /* skip the inode if the file size is too small */
> if (eofb->eof_flags & XFS_EOF_FLAGS_MINFILESIZE &&
> XFS_ISIZE(ip) < eofb->eof_min_file_size)

Oh, I see you are just copying other code. How did I miss that in a
past review? :(

Hmmm - it looks like there's a bunch of them in xfs_inode_match_id()
as well, and you touched all those if() statements in a previous
patch. can you go back to the patch that touches
xfs_inode_match_id() and add the extra () there as well?

> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index abbbdcf..e63e359 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1636,6 +1636,8 @@ xfs_file_ioctl(
> !gid_valid(keofb.eof_gid))
> return XFS_ERROR(EINVAL);
>
> + keofb.eof_flags |= XFS_EOF_FLAGS_PERM_CHECK;

We should be checking for the fs being RO here and aborting if it
is.