Request for inclusion of 4dfce57db635 ("xfs: fix up xfs_swap_extent_forks inline extent handling") in stable

Commit Message

Nikolay Borisov March 27, 2017, 7:31 a.m. UTC

Hello,


The commit in the subject was tagged as stable but I guess it got missed
being included into stable. Without these stable kernels crash on
xfs/118. I've attached backports for both 3.12 and 4.4 and also ran a
regtest with xfstest with no regressions showing up.

Regards,
Nikolay
From: Eric Sandeen <[e-mail]>
Date: Tue, 8 Nov 2016 12:55:18 +1100
Subject: xfs: fix up xfs_swap_extent_forks inline extent handling

There have been several reports over the years of NULL pointer
dereferences in xfs_trans_log_inode during xfs_fsr processes,
when the process is doing an fput and tearing down extents
on the temporary inode, something like:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
PID: 29439  TASK: ffff880550584fa0  CPU: 6   COMMAND: "xfs_fsr"
    [exception RIP: xfs_trans_log_inode+0x10]
 #9 [ffff8800a57bbbe0] xfs_bunmapi at ffffffffa037398e [xfs]
#10 [ffff8800a57bbce8] xfs_itruncate_extents at ffffffffa0391b29 [xfs]
#11 [ffff8800a57bbd88] xfs_inactive_truncate at ffffffffa0391d0c [xfs]
#12 [ffff8800a57bbdb8] xfs_inactive at ffffffffa0392508 [xfs]
#13 [ffff8800a57bbdd8] xfs_fs_evict_inode at ffffffffa035907e [xfs]
#14 [ffff8800a57bbe00] evict at ffffffff811e1b67
#15 [ffff8800a57bbe28] iput at ffffffff811e23a5
#16 [ffff8800a57bbe58] dentry_kill at ffffffff811dcfc8
#17 [ffff8800a57bbe88] dput at ffffffff811dd06c
#18 [ffff8800a57bbea8] __fput at ffffffff811c823b
#19 [ffff8800a57bbef0] ____fput at ffffffff811c846e
#20 [ffff8800a57bbf00] task_work_run at ffffffff81093b27
#21 [ffff8800a57bbf30] do_notify_resume at ffffffff81013b0c
#22 [ffff8800a57bbf50] int_signal at ffffffff8161405d

As it turns out, this is because the i_itemp pointer, along
with the d_ops pointer, has been overwritten with zeros
when we tear down the extents during truncate.  When the in-core
inode fork on the temporary inode used by xfs_fsr was originally
set up during the extent swap, we mistakenly looked at di_nextents
to determine whether all extents fit inline, but this misses extents
generated by speculative preallocation; we should be using if_bytes
instead.

This mistake corrupts the in-memory inode, and code in
xfs_iext_remove_inline eventually gets bad inputs, causing
it to memmove and memset incorrect ranges; this became apparent
because the two values in ifp->if_u2.if_inline_ext[1] contained
what should have been in d_ops and i_itemp; they were memmoved due
to incorrect array indexing and then the original locations
were zeroed with memset, again due to an array overrun.

Fix this by properly using i_df.if_bytes to determine the number
of extents, not di_nextents.

Thanks to dchinner for looking at this with me and spotting the
root cause.

[nborisov: Backported to 3.12]

Cc: [e-mail]
Signed-off-by: Eric Sandeen <[e-mail]>
Reviewed-by: Brian Foster <[e-mail]>
Signed-off-by: Dave Chinner <[e-mail]>
Signed-off-by: Nikolay Borisov <[e-mail]>
--
 fs/xfs/xfs_bmap_util.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Comments

Jiri Slaby March 27, 2017, 8:17 a.m. UTC | #1

On 03/27/2017, 09:31 AM, Nikolay Borisov wrote:
> Hello,
> 
> 
> The commit in the subject was tagged as stable but I guess it got missed
> being included into stable. Without these stable kernels crash on
> xfs/118. I've attached backports for both 3.12 and 4.4 and also ran a
> regtest with xfstest with no regressions showing up.

Applied to 3.12, thanks!

Patch

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index d756da515b15..8336701a281c 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1788,6 +1788,7 @@  xfs_swap_extents(
 	xfs_trans_t	*tp;
 	xfs_bstat_t	*sbp = &sxp->sx_stat;
 	xfs_ifork_t	*tempifp, *ifp, *tifp;
+	xfs_extnum_t	nextents;
 	int		src_log_flags, target_log_flags;
 	int		error = 0;
 	int		aforkblks = 0;
@@ -1974,7 +1975,8 @@  xfs_swap_extents(
 		 * pointer.  Otherwise it's already NULL or
 		 * pointing to the extent.
 		 */
-		if (ip->i_d.di_nextents <= XFS_INLINE_EXTS) {
+		nextents = ip->i_df.if_bytes / (uint)sizeof(xfs_bmbt_rec_t);
+		if (nextents <= XFS_INLINE_EXTS) {
 			ifp->if_u1.if_extents =
 				ifp->if_u2.if_inline_ext;
 		}
@@ -1993,7 +1995,8 @@  xfs_swap_extents(
 		 * pointer.  Otherwise it's already NULL or
 		 * pointing to the extent.
 		 */
-		if (tip->i_d.di_nextents <= XFS_INLINE_EXTS) {
+		nextents = tip->i_df.if_bytes / (uint)sizeof(xfs_bmbt_rec_t);
+		if (nextents <= XFS_INLINE_EXTS) {
 			tifp->if_u1.if_extents =
 				tifp->if_u2.if_inline_ext;
 		}