From: Dave Chinner <dchinner@xxxxxxxxxx>
Resulting in a UAF if the shrinker races with some other dquot
freeing mechanism that sets XFS_DQFLAG_FREEING before the dquot is
removed from the LRU. This can occur if a dquot purge races with
drop_caches.
Reported-by: syzbot+912776840162c13db1a3@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
fs/xfs/xfs_qm.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 18bb4ec4d7c9..ff53d40a2dae 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -422,6 +422,14 @@ xfs_qm_dquot_isolate(
if (!xfs_dqlock_nowait(dqp))
goto out_miss_busy;
+ /*
+ * If something else is freeing this dquot and hasn't yet removed it
+ * from the LRU, leave it for the freeing task to complete the freeing
+ * process rather than risk it being free from under us here.
+ */
+ if (dqp->q_flags & XFS_DQFLAG_FREEING)
+ goto out_miss_unlock;
+
/*
* This dquot has acquired a reference in the meantime remove it from
* the freelist and try again.
@@ -441,10 +449,8 @@ xfs_qm_dquot_isolate(
* skip it so there is time for the IO to complete before we try to
* reclaim it again on the next LRU pass.
*/
- if (!xfs_dqflock_nowait(dqp)) {
- xfs_dqunlock(dqp);
- goto out_miss_busy;
- }
+ if (!xfs_dqflock_nowait(dqp))
+ goto out_miss_unlock;
if (XFS_DQ_IS_DIRTY(dqp)) {
struct xfs_buf *bp = NULL;
@@ -478,6 +484,8 @@ xfs_qm_dquot_isolate(
XFS_STATS_INC(dqp->q_mount, xs_qm_dqreclaims);
return LRU_REMOVED;
+out_miss_unlock:
+ xfs_dqunlock(dqp);
out_miss_busy:
trace_xfs_dqreclaim_busy(dqp);
XFS_STATS_INC(dqp->q_mount, xs_qm_dqreclaim_misses);
--
2.38.1
