rxrpc: Fix call ref leak

When sendmsg() finds a call to continue on with, if the call is in an
inappropriate state, it doesn't release the ref it just got on that call
before returning an error.

This causes the following symptom to show up with kasan:

	BUG: KASAN: use-after-free in rxrpc_send_keepalive+0x8a2/0x940
	net/rxrpc/output.c:635
	Read of size 8 at addr ffff888064219698 by task kworker/0:3/11077

where line 635 is:

	whdr.epoch	= htonl(peer->local->rxnet->epoch);

The local endpoint (which cannot be pinned by the call) has been released,
but not the peer (which is pinned by the call).

Fix this by releasing the call in the error path.

Fixes: 37411cad633f ("rxrpc: Fix potential NULL-pointer exception")
Reported-by: syzbot+d850c266e3df14da1d31@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 6a1547b270fef519fc5c334ced74b728f6484d28..22f51a7e356ee7c681f2ee9338009c0ded19b998 100644 (file)
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -661,6 +661,7 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
                case RXRPC_CALL_SERVER_PREALLOC:
                case RXRPC_CALL_SERVER_SECURING:
                case RXRPC_CALL_SERVER_ACCEPTING:
+                       rxrpc_put_call(call, rxrpc_call_put);
                        ret = -EBUSY;
                        goto error_release_sock;
                default: