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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Baptiste Lepers <baptiste.lepers@gmail.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 153/289] sunrpc: Fix misplaced barrier in call_decode
Date:   Mon, 17 May 2021 16:01:18 +0200
Message-Id: <20210517140310.294436841@linuxfoundation.org>
In-Reply-To: <20210517140305.140529752@linuxfoundation.org>
References: <20210517140305.140529752@linuxfoundation.org>
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From: Baptiste Lepers <baptiste.lepers@gmail.com>

[ Upstream commit f8f7e0fb22b2e75be55f2f0c13e229e75b0eac07 ]

Fix a misplaced barrier in call_decode. The struct rpc_rqst is modified
as follows by xprt_complete_rqst:

req->rq_private_buf.len = copied;
/* Ensure all writes are done before we update */
/* req->rq_reply_bytes_recvd */
smp_wmb();
req->rq_reply_bytes_recvd = copied;

And currently read as follows by call_decode:

smp_rmb(); // misplaced
if (!req->rq_reply_bytes_recvd)
   goto out;
req->rq_rcv_buf.len = req->rq_private_buf.len;

This patch places the smp_rmb after the if to ensure that
rq_reply_bytes_recvd and rq_private_buf.len are read in order.

Fixes: 9ba828861c56a ("SUNRPC: Don't try to parse incomplete RPC messages")
Signed-off-by: Baptiste Lepers <baptiste.lepers@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sunrpc/clnt.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 69d8843a26e0..4a0e8e458a9a 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2459,12 +2459,6 @@ call_decode(struct rpc_task *task)
 		task->tk_flags &= ~RPC_CALL_MAJORSEEN;
 	}
 
-	/*
-	 * Ensure that we see all writes made by xprt_complete_rqst()
-	 * before it changed req->rq_reply_bytes_recvd.
-	 */
-	smp_rmb();
-
 	/*
 	 * Did we ever call xprt_complete_rqst()? If not, we should assume
 	 * the message is incomplete.
@@ -2473,6 +2467,11 @@ call_decode(struct rpc_task *task)
 	if (!req->rq_reply_bytes_recvd)
 		goto out;
 
+	/* Ensure that we see all writes made by xprt_complete_rqst()
+	 * before it changed req->rq_reply_bytes_recvd.
+	 */
+	smp_rmb();
+
 	req->rq_rcv_buf.len = req->rq_private_buf.len;
 	trace_rpc_xdr_recvfrom(task, &req->rq_rcv_buf);
 
-- 
2.30.2