netdev - Re: KMSAN: uninit-value in ebt_stp_mt

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Date:   Thu, 7 Jun 2018 19:34:10 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+da4494182233c23a5fcf@...kaller.appspotmail.com>
Cc:     bridge@...ts.linux-foundation.org, coreteam@...filter.org,
        David Miller <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, netfilter-devel@...r.kernel.org,
        Pablo Neira Ayuso <pablo@...filter.org>,
        stephen hemminger <stephen@...workplumber.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KMSAN: uninit-value in ebt_stp_mt_check (2)

On Thu, Jun 7, 2018 at 7:29 PM, syzbot
<syzbot+da4494182233c23a5fcf@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    c6a6aed994b6 kmsan: remove dead code to trigger syzbot build
> git tree:       https://github.com/google/kmsan.git/master
> console output: https://syzkaller.appspot.com/x/log.txt?x=17bde74f800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=848e40757852af3e
> dashboard link: https://syzkaller.appspot.com/bug?extid=da4494182233c23a5fcf
> compiler:       clang version 7.0.0 (trunk 334104)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+da4494182233c23a5fcf@...kaller.appspotmail.com

Hi Stephen,

This strikes again.

The first part of the check is par->nft_compat. I don't see where
ebt_check_entry initializes it. Should it? Or matches should not look at it?



> ==================================================================
> BUG: KMSAN: uninit-value in ebt_stp_mt_check+0x24b/0x450
> net/bridge/netfilter/ebt_stp.c:162
> CPU: 0 PID: 12006 Comm: syz-executor7 Not tainted 4.17.0+ #3
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x185/0x1d0 lib/dump_stack.c:113
>  kmsan_report+0x149/0x260 mm/kmsan/kmsan.c:1084
>  __msan_warning_32+0x6e/0xc0 mm/kmsan/kmsan_instr.c:620
>  ebt_stp_mt_check+0x24b/0x450 net/bridge/netfilter/ebt_stp.c:162
>  xt_check_match+0x1438/0x1650 net/netfilter/x_tables.c:506
>  ebt_check_match net/bridge/netfilter/ebtables.c:372 [inline]
>  ebt_check_entry net/bridge/netfilter/ebtables.c:702 [inline]
>  translate_table+0x4e88/0x6120 net/bridge/netfilter/ebtables.c:943
>  do_replace_finish+0x1258/0x2ea0 net/bridge/netfilter/ebtables.c:999
>  do_replace+0x719/0x780 net/bridge/netfilter/ebtables.c:1138
>  do_ebt_set_ctl+0x2ab/0x3c0 net/bridge/netfilter/ebtables.c:1517
>  nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
>  nf_setsockopt+0x47c/0x4e0 net/netfilter/nf_sockopt.c:115
>  ip_setsockopt+0x24b/0x2b0 net/ipv4/ip_sockglue.c:1251
>  udp_setsockopt+0x108/0x1b0 net/ipv4/udp.c:2416
>  sock_common_setsockopt+0x13b/0x170 net/core/sock.c:3039
>  __sys_setsockopt+0x496/0x540 net/socket.c:1903
>  __do_sys_setsockopt net/socket.c:1914 [inline]
>  __se_sys_setsockopt net/socket.c:1911 [inline]
>  __x64_sys_setsockopt+0x15c/0x1c0 net/socket.c:1911
>  do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x4559f9
> RSP: 002b:00007f45b9246c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
> RAX: ffffffffffffffda RBX: 00007f45b92476d4 RCX: 00000000004559f9
> RDX: 0000000000000080 RSI: 0000000000000000 RDI: 0000000000000014
> RBP: 000000000072bea0 R08: 0000000000000300 R09: 0000000000000000
> R10: 0000000020000480 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000004c0d6d R14: 00000000004d07c8 R15: 0000000000000000
>
> Local variable description: ----mtpar.i@...nslate_table
> Variable was created at:
>  translate_table+0xbb/0x6120 net/bridge/netfilter/ebtables.c:831
>  do_replace_finish+0x1258/0x2ea0 net/bridge/netfilter/ebtables.c:999
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
>
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