[PATCH 3.16 021/370] xfs: fix up xfs_swap_extent_forks inline extent handling

Ben Hutchings
2017-03-10T14:27:50Z

From: Eric Sandeen <sandeen@sandeen.net>

commit 4dfce57db6354603641132fac3c887614e3ebe81 upstream.

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.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
[bwh: Backported to 3.16: adjust indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/xfs/xfs_bmap_util.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1632,6 +1632,7 @@ xfs_swap_extents(
int error = 0;
int aforkblks = 0;
int taforkblks = 0;
+ xfs_extnum_t nextents;
__uint64_t tmp;
int lock_flags;

@@ -1833,7 +1834,8 @@ 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;
}
@@ -1852,7 +1854,8 @@ 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;
}