tipc: fix an use-after-free issue in tipc_recvmsg

commit cc19862ffe454a5b632ca202e5a51bfec9f89fd2 upstream.

syzbot reported an use-after-free crash:

  BUG: KASAN: use-after-free in tipc_recvmsg+0xf77/0xf90 net/tipc/socket.c:1979
  Call Trace:
   tipc_recvmsg+0xf77/0xf90 net/tipc/socket.c:1979
   sock_recvmsg_nosec net/socket.c:943 [inline]
   sock_recvmsg net/socket.c:961 [inline]
   sock_recvmsg+0xca/0x110 net/socket.c:957
   tipc_conn_rcv_from_sock+0x162/0x2f0 net/tipc/topsrv.c:398
   tipc_conn_recv_work+0xeb/0x190 net/tipc/topsrv.c:421
   process_one_work+0x98d/0x1630 kernel/workqueue.c:2276
   worker_thread+0x658/0x11f0 kernel/workqueue.c:2422

As Hoang pointed out, it was caused by skb_cb->bytes_read still accessed
after calling tsk_advance_rx_queue() to free the skb in tipc_recvmsg().

This patch is to fix it by accessing skb_cb->bytes_read earlier than
calling tsk_advance_rx_queue().

Fixes: f4919ff59c28 ("tipc: keep the skb in rcv queue until the whole data is read")
Reported-by: syzbot+e6741b97d5552f97c24d@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 963047c..91230ee 100644 (file)
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -1980,10 +1980,12 @@ static int tipc_recvmsg(struct socket *sock, struct msghdr *m,
                tipc_node_distr_xmit(sock_net(sk), &xmitq);
        }
 
-       if (!skb_cb->bytes_read)
-               tsk_advance_rx_queue(sk);
+       if (skb_cb->bytes_read)
+               goto exit;
+
+       tsk_advance_rx_queue(sk);
 
-       if (likely(!connected) || skb_cb->bytes_read)
+       if (likely(!connected))
                goto exit;
 
        /* Send connection flow control advertisement when applicable */