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From:   Pavel Skripkin <paskripkin@gmail.com>
To:     santosh.shilimkar@oracle.com, davem@davemloft.net, kuba@kernel.org
Cc:     netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
        rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org,
        Pavel Skripkin <paskripkin@gmail.com>,
        syzbot+5134cdf021c4ed5aaa5f@syzkaller.appspotmail.com
Subject: [PATCH] net: rds: fix memory leak in rds_recvmsg
Date:   Mon,  7 Jun 2021 22:41:02 +0300
Message-Id: <20210607194102.2883-1-paskripkin@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Syzbot reported memory leak in rds. The problem
was in unputted refcount in case of error.

int rds_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
		int msg_flags)
{
...

	if (!rds_next_incoming(rs, &inc)) {
		...
	}

After this "if" inc refcount incremented and

	if (rds_cmsg_recv(inc, msg, rs)) {
		ret = -EFAULT;
		goto out;
	}
...
out:
	return ret;
}

in case of rds_cmsg_recv() fail the refcount won't be
decremented. And it's easy to see from ftrace log, that
rds_inc_addref() don't have rds_inc_put() pair in
rds_recvmsg() after rds_cmsg_recv()

 1)               |  rds_recvmsg() {
 1)   3.721 us    |    rds_inc_addref();
 1)   3.853 us    |    rds_message_inc_copy_to_user();
 1) + 10.395 us   |    rds_cmsg_recv();
 1) + 34.260 us   |  }

Fixes: bdbe6fbc6a2f ("RDS: recv.c")
Reported-and-tested-by: syzbot+5134cdf021c4ed5aaa5f@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
 net/rds/recv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rds/recv.c b/net/rds/recv.c
index 4db109fb6ec2..3fa16c339bfe 100644
--- a/net/rds/recv.c
+++ b/net/rds/recv.c
@@ -714,7 +714,7 @@ int rds_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 
 		if (rds_cmsg_recv(inc, msg, rs)) {
 			ret = -EFAULT;
-			goto out;
+			goto out_put;
 		}
 		rds_recvmsg_zcookie(rs, msg);
 
@@ -740,6 +740,7 @@ int rds_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 		break;
 	}
 
+out_put:
 	if (inc)
 		rds_inc_put(inc);
 
-- 
2.31.1