From ba099fe50c0aeb682382facbefc5d6aaa83e7226 Mon Sep 17 00:00:00 2001
From: Xin Long <lucien.xin@gmail.com>
Date: Fri, 23 Jul 2021 13:25:36 -0400
Subject: [PATCH] tipc: fix an use-after-free issue in tipc_recvmsg
Git-commit: cc19862ffe454a5b632ca202e5a51bfec9f89fd2
Patch-mainline: v5.15-rc1
References: stable-5.14.7

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 net/tipc/socket.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index a155cfaf01f2..e3105ba407c7 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -1979,10 +1979,12 @@ 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 */
-- 
2.26.2