Subject: [PATCH AUTOSEL 4.19 445/671] xprtrdma: Fix use-after-free in rpcrdma_post_recvs

From: Sasha Levin <[email-masked]>
Date: Thu, 16 Jan 2020 12:01:23 -0500

From: Chuck Lever <[email-masked]>

[ Upstream commit 2d0abe36cf13fb7b577949fd1539326adddcc9bc ]

Dereference wr->next /before/ the memory backing wr has been
released. This issue was found by code inspection. It is not
expected to be a significant problem because it is in an error
path that is almost never executed.

Fixes: 7c8d9e7c8863 ("xprtrdma: Move Receive posting to ... ")
Signed-off-by: Chuck Lever <[email-masked]>
Signed-off-by: Anna Schumaker <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 net/sunrpc/xprtrdma/verbs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 5ddbf227e7c6..2a1d8ec7f706 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1558,10 +1558,11 @@ rpcrdma_post_recvs(struct rpcrdma_xprt *r_xprt, bool temp)
 	rc = ib_post_recv(r_xprt->rx_ia.ri_id->qp, wr,
 			  (const struct ib_recv_wr **)&bad_wr);
 	if (rc) {
-		for (wr = bad_wr; wr; wr = wr->next) {
+		for (wr = bad_wr; wr;) {
 			struct rpcrdma_rep *rep;
 
 			rep = container_of(wr, struct rpcrdma_rep, rr_recv_wr);
+			wr = wr->next;
 			rpcrdma_recv_buffer_put(rep);
 			--count;
 		}
-- 
2.20.1