linux-kernel - [PATCH net] rxrpc: Fix potential NULL-pointer exception

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Message-ID: <148849717388.26285.3477243497908119377.stgit@warthog.procyon.org.uk>
Date:   Thu, 02 Mar 2017 23:26:13 +0000
From:   David Howells <dhowells@...hat.com>
To:     netdev@...r.kernel.org
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net] rxrpc: Fix potential NULL-pointer exception

Fix a potential NULL-pointer exception in rxrpc_do_sendmsg().  The call
state check that I added should have gone into the else-body of the
if-statement where we actually have a call to check.

Found by CoverityScan CID#1414316 ("Dereference after null check").

Fixes: 540b1c48c37a ("rxrpc: Fix deadlock between call creation and sendmsg/recvmsg")
Reported-by: Colin Ian King <colin.king@...onical.com>
Signed-off-by: David Howells <dhowells@...hat.com>
---

 net/rxrpc/sendmsg.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 75c5179227f2..344c2a60627b 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -518,6 +518,13 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
 		ret = -EBADSLT;
 		if (cmd != RXRPC_CMD_SEND_DATA)
 			goto error_release_sock;
+		call = rxrpc_new_client_call_for_sendmsg(rx, msg, user_call_ID,
+							 exclusive);
+		/* The socket is now unlocked... */
+		if (IS_ERR(call))
+			return PTR_ERR(call);
+		/* ... and we have the call lock. */
+	} else {
 		switch (READ_ONCE(call->state)) {
 		case RXRPC_CALL_UNINITIALISED:
 		case RXRPC_CALL_CLIENT_AWAIT_CONN:
@@ -529,13 +536,7 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
 		default:
 			break;
 		}
-		call = rxrpc_new_client_call_for_sendmsg(rx, msg, user_call_ID,
-							 exclusive);
-		/* The socket is now unlocked... */
-		if (IS_ERR(call))
-			return PTR_ERR(call);
-		/* ... and we have the call lock. */
-	} else {
+
 		ret = mutex_lock_interruptible(&call->user_mutex);
 		release_sock(&rx->sk);
 		if (ret < 0) {