[PATCH 63/67] xfs: fix a use after free in xfs_defer_finish_recovery

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From: Christoph Hellwig <hch@xxxxxx>

Source kernel commit: 4f6ac47b55e3ce6e982807928d6074ec105ab66e

dfp will be freed by ->recover_work and thus the tracepoint in case
of an error can lead to a use after free.

Store the defer ops in a local variable to avoid that.

Fixes: 7f2f7531e0d4 ("xfs: store an ops pointer in struct xfs_defer_pending")
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
Signed-off-by: Chandan Babu R <chandanbabu@xxxxxxxxxx>
Signed-off-by: Carlos Maiolino <cem@xxxxxxxxxx>
 libxfs/xfs_defer.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libxfs/xfs_defer.c b/libxfs/xfs_defer.c
index 077e99298..5bdc8f5a2 100644
--- a/libxfs/xfs_defer.c
+++ b/libxfs/xfs_defer.c
@@ -909,12 +909,14 @@ xfs_defer_finish_recovery(
 	struct xfs_defer_pending	*dfp,
 	struct list_head		*capture_list)
+	const struct xfs_defer_op_type	*ops = dfp->dfp_ops;
 	int				error;
-	error = dfp->dfp_ops->recover_work(dfp, capture_list);
+	/* dfp is freed by recover_work and must not be accessed afterwards */
+	error = ops->recover_work(dfp, capture_list);
 	if (error)
 		trace_xlog_intent_recovery_failed(mp, error,
-				dfp->dfp_ops->recover_work);
+				ops->recover_work);
 	return error;

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