netdev - Re: [PATCH net-next] tipc: eliminate complaint of KMSAN uninit-value in tipc_conn_rcv

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Date:   Fri, 18 May 2018 14:10:20 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Ying Xue <ying.xue@...driver.com>
Cc:     netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jon Maloy <jon.maloy@...csson.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [PATCH net-next] tipc: eliminate complaint of KMSAN uninit-value
 in tipc_conn_rcv_sub

On Fri, May 18, 2018 at 1:50 PM, Ying Xue <ying.xue@...driver.com> wrote:
> As variable s of struct tipc_subscr type is not initialized
> in tipc_conn_rcv_from_sock() before it is used in tipc_conn_rcv_sub(),
> KMSAN reported the following uninit-value type complaint:
>
> ==================================================================
> 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
> ==================================================================
> Kernel panic - not syncing: panic_on_warn set ...
>
> CPU: 0 PID: 66 Comm: kworker/u4:4 Tainted: G    B             4.17.0-rc3+
> 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
>   panic+0x39d/0x940 kernel/panic.c:184
>   kmsan_report+0x238/0x240 mm/kmsan/kmsan.c:1083
>   __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
> Dumping ftrace buffer:
>     (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
> Reported-by: syzbot+8951a3065ee7fd6d6e23@...kaller.appspotmail.com
> Signed-off-by: Ying Xue <ying.xue@...driver.com>
> ---
>  net/tipc/topsrv.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/tipc/topsrv.c b/net/tipc/topsrv.c
> index c8e34ef..fe47a62 100644
> --- a/net/tipc/topsrv.c
> +++ b/net/tipc/topsrv.c
> @@ -397,6 +397,7 @@ static int tipc_conn_rcv_from_sock(struct tipc_conn *con)
>         struct kvec iov;
>         int ret;
>
> +       memset(&s, 0, sizeof(s));
>         iov.iov_base = &s;
>         iov.iov_len = sizeof(s);
>         msg.msg_name = NULL;


Isn't the kernel bug here that sock_recvmsg does a short read? It
seems that sock_recvmsg should initialize all of s.