[PATCH] RDMA/core: Fix member use-after-free in process_group_error()

[Wentao Liang <vulab@iscas.ac.cn>]

If the callback on the error path returns non-zero after a concurrent
ib_sa_free_multicast() already dropped the initial member reference,
dropping our temporary reference completes the waiter, which then frees
the member before ib_sa_free_multicast() dereferences it again.

Only free the multicast member when our reference decrement was not
the last one; otherwise the concurrent free is already in flight.

Fixes: faec2f7b96b5 ("IB/sa: Track multicast join/leave requests")
Cc: stable@vger.kernel.org
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
---
 drivers/infiniband/core/multicast.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/multicast.c b/drivers/infiniband/core/multicast.c
index bea7df3dd8f3..aa6fdac5fcde 100644
--- a/drivers/infiniband/core/multicast.c
+++ b/drivers/infiniband/core/multicast.c
@@ -409,8 +409,9 @@ static void process_group_error(struct mcast_group *group)
 
 		ret = member->multicast.callback(-ENETRESET,
 						 &member->multicast);
-		deref_member(member);
-		if (ret)
+		if (refcount_dec_and_test(&member->refcount))
+			complete(&member->comp);
+		else if (ret)
 			ib_sa_free_multicast(&member->multicast);
 		spin_lock_irq(&group->lock);
 	}
-- 
2.34.1