linux-kernel - Re: KASAN: slab-out-of-bounds Read in bpf_csum

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Date:   Mon, 4 Jun 2018 07:36:57 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+efae31b384d5badbd620@...kaller.appspotmail.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: slab-out-of-bounds Read in bpf_csum_update

On Mon, Jun 4, 2018 at 1:36 AM, syzbot
<syzbot+efae31b384d5badbd620@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    0512e0134582 Merge tag 'xfs-4.17-fixes-3' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17eb2d7b800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=968b0b23c7854c0b
> dashboard link: https://syzkaller.appspot.com/bug?extid=efae31b384d5badbd620
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=162c6def800000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14fe3db7800000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+efae31b384d5badbd620@...kaller.appspotmail.com
>
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in ____bpf_csum_update net/core/filter.c:1679
> [inline]
> BUG: KASAN: slab-out-of-bounds in bpf_csum_update+0xb4/0xc0
> net/core/filter.c:1673
> Read of size 1 at addr ffff8801d9235b50 by task syz-executor507/4513
>
> CPU: 0 PID: 4513 Comm: syz-executor507 Not tainted 4.17.0-rc7+ #78
> 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+0x1b9/0x294 lib/dump_stack.c:113
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
>  __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
>  ____bpf_csum_update net/core/filter.c:1679 [inline]
>  bpf_csum_update+0xb4/0xc0 net/core/filter.c:1673

/\/\/\/\/\

Are there any known bugs with unwind through bpf functions?

> Allocated by task 0:
> (stack is not available)
>
> Freed by task 0:
> (stack is not available)
>
> The buggy address belongs to the object at ffff8801d9235a40
>  which belongs to the cache skbuff_head_cache of size 232
> The buggy address is located 40 bytes to the right of
>  232-byte region [ffff8801d9235a40, ffff8801d9235b28)
> The buggy address belongs to the page:
> page:ffffea0007648d40 count:1 mapcount:0 mapping:ffff8801d9235040 index:0x0
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffff8801d9235040 0000000000000000 000000010000000c
> raw: ffffea00074360a0 ffff8801d944d848 ffff8801d9bdd6c0 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff8801d9235a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8801d9235a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>
>> ffff8801d9235b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>
>                                                  ^
>  ffff8801d9235b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8801d9235c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> 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.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
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