netdev - [net 1/6] tipc: fix uninit-value in in tipc_conn_rcv

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Date:   Mon, 14 Jan 2019 17:22:24 +0800
From:   Ying Xue <ying.xue@...driver.com>
To:     <netdev@...r.kernel.org>
CC:     <jon.maloy@...csson.com>, <tipc-discussion@...ts.sourceforge.net>,
        <syzkaller-bugs@...glegroups.com>
Subject: [net 1/6] tipc: fix uninit-value in in tipc_conn_rcv_sub

syzbot reported:

BUG: KMSAN: uninit-value in tipc_conn_rcv_sub+0x184/0x950 net/tipc/topsrv.c:373
CPU: 0 PID: 66 Comm: kworker/u4:4 Not tainted 4.17.0-rc3+ #88
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: tipc_rcv tipc_conn_recv_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x185/0x1d0 lib/dump_stack.c:113
 kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
 __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
 tipc_conn_rcv_sub+0x184/0x950 net/tipc/topsrv.c:373
 tipc_conn_rcv_from_sock net/tipc/topsrv.c:409 [inline]
 tipc_conn_recv_work+0x3cd/0x560 net/tipc/topsrv.c:424
 process_one_work+0x12c6/0x1f60 kernel/workqueue.c:2145
 worker_thread+0x113c/0x24f0 kernel/workqueue.c:2279
 kthread+0x539/0x720 kernel/kthread.c:239
 ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:412

Local variable description: ----s.i@...c_conn_recv_work
Variable was created at:
 tipc_conn_recv_work+0x65/0x560 net/tipc/topsrv.c:419
 process_one_work+0x12c6/0x1f60 kernel/workqueue.c:2145

In tipc_conn_rcv_from_sock(), it always supposes the length of message
received from sock_recvmsg() is not smaller than the size of struct
tipc_subscr. However, this assumption is false. Especially when the
length of received message is shorter than struct tipc_subscr size,
we will end up touching uninitialized fields in tipc_conn_rcv_sub().

Reported-by: syzbot+8951a3065ee7fd6d6e23@...kaller.appspotmail.com
Reported-by: syzbot+75e6e042c5bbf691fc82@...kaller.appspotmail.com
Signed-off-by: Ying Xue <ying.xue@...driver.com>
---
 net/tipc/topsrv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/tipc/topsrv.c b/net/tipc/topsrv.c
index efb16f6..a457c0f 100644
--- a/net/tipc/topsrv.c
+++ b/net/tipc/topsrv.c
@@ -398,7 +398,7 @@ static int tipc_conn_rcv_from_sock(struct tipc_conn *con)
 	ret = sock_recvmsg(con->sock, &msg, MSG_DONTWAIT);
 	if (ret == -EWOULDBLOCK)
 		return -EWOULDBLOCK;
-	if (ret > 0) {
+	if (ret == sizeof(s)) {
 		read_lock_bh(&sk->sk_callback_lock);
 		ret = tipc_conn_rcv_sub(srv, con, &s);
 		read_unlock_bh(&sk->sk_callback_lock);
-- 
2.7.4