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xfs: fix use after free in buf log item unlock assert 

The xfs_buf_log_item ->iop_unlock() callback asserts that the buffer
is unlocked when either non-stale or aborted. This assert occurs
after the bli refcount has been dropped and the log item potentially
freed. The aborted check is thus a potential use after free. This
problem has been reproduced with KASAN enabled via generic/475.

Fix up xfs_buf_item_unlock() to query aborted state before the bli
reference is dropped to prevent a potential use after free.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Brian Foster 2019-04-12 07:39:19 -07:00 committed by Darrick J. Wong
parent dc4060a5dc
commit 4d09807f20
1 changed files with 3 additions and 1 deletions
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4
fs/xfs/xfs_buf_item.c
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@ -605,6 +605,8 @@ xfs_buf_item_unlock(
#if defined(DEBUG) || defined(XFS_WARN)
bool ordered = bip->bli_flags & XFS_BLI_ORDERED;
bool dirty = bip->bli_flags & XFS_BLI_DIRTY;
bool aborted = test_bit(XFS_LI_ABORTED,
&lip->li_flags);
#endif
trace_xfs_buf_item_unlock(bip);
@ -633,7 +635,7 @@ xfs_buf_item_unlock(
released = xfs_buf_item_put(bip);
if (hold || (stale && !released))
return;
ASSERT(!stale || test_bit(XFS_LI_ABORTED, &lip->li_flags));
ASSERT(!stale || aborted);
xfs_buf_relse(bp);
}