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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Fri, 20 Jul 2018 10:00:34 +0200
Message-ID: <CACT4Y+YRmX2ROxWZcT4w-NHR76cVV4_U6-Y0T=x4on67r8dNzQ@mail.gmail.com>
Subject: Re: KASAN: use-after-free Read in l2tp_session_create
To:     James Chapman <jchapman@katalix.com>
Cc:     David Miller <davem@davemloft.net>,
        "Reshetova, Elena" <elena.reshetova@intel.com>,
        Hans Liljestrand <ishkamiel@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Greg Hackmann <ghackmann@google.com>,
        syzbot <syzbot+065d0fc357520c8f6039@syzkaller.appspotmail.com>,
        Guillaume Nault <g.nault@alphalink.fr>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Fri, Jul 20, 2018 at 9:53 AM, James Chapman <jchapman@katalix.com> wrote:
> On 18/07/18 12:00, Dmitry Vyukov wrote:
>> On Tue, Jan 16, 2018 at 7:29 PM, syzbot
>> <syzbot+065d0fc357520c8f6039@syzkaller.appspotmail.com> wrote:
>>> Hello,
>>>
>>> syzkaller hit the following crash on
>>> a8750ddca918032d6349adbf9a4b6555e7db20da
>>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
>>> compiler: gcc (GCC) 7.1.1 20170620
>>> .config is attached
>>> Raw console output is attached.
>>> Unfortunately, I don't have any reproducer for this bug yet.
>>>
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+065d0fc357520c8f6039@syzkaller.appspotmail.com
>>> It will help syzbot understand when the bug is fixed. See footer for
>>> details.
>>> If you forward the report, please keep this part and the footer.
>>
>> James,
>>
>> Did you fix this? You asked syzbot to test a fix for this bug some time ago.
>> If yes, did you include the Reported-by tag in the commit? This bug is
>> still considered open by syzbot. But it stopped happening ~4 months
>> ago:
>
> Yes, I think this has been fixed now. I think it was fixed by
> Guillaume's 6b9f34239b00e6956a267abed2bc559ede556ad6 that was actually
> to fix another syzbot bug fbeeb5c3b538e8545644 which looks similar to
> this one.
>
>> https://syzkaller.appspot.com/bug?id=6fed0854381422329e78d7e16fb9cf4af8c9aef1
>> We are also seeing these crashes in 4.4 and 4.9, it would be good to
>> backport the fix.
>
> It looks like 6b9f34239b00e6956a267abed2bc559ede556ad6 hasn't made it to
> 4.9 or 4.4.

Thanks for the update!

Let's tell syzbot that this is fixed:

#syz fix: l2tp: fix races in tunnel creation

Greg H: so this is probably the patch we need.

+Greg KH: I think we need this in stable, we hit this in both 4.4 and 4.9.


>>> ==================================================================
>>> BUG: KASAN: use-after-free in l2tp_session_create+0xa6d/0xc60
>>> net/l2tp/l2tp_core.c:1757
>>> Read of size 4 at addr ffff8801d80ad868 by task syz-executor3/5462
>>>
>>> CPU: 0 PID: 5462 Comm: syz-executor3 Not tainted 4.15.0-rc8+ #263
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>>> Google 01/01/2011
>>> Call Trace:
>>>  __dump_stack lib/dump_stack.c:17 [inline]
>>>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>>>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>>>  kasan_report_error mm/kasan/report.c:351 [inline]
>>>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>>>  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
>>>  l2tp_session_create+0xa6d/0xc60 net/l2tp/l2tp_core.c:1757
>>>  pppol2tp_connect+0xed7/0x1dd0 net/l2tp/l2tp_ppp.c:748
>>>  SYSC_connect+0x213/0x4a0 net/socket.c:1621
>>>  SyS_connect+0x24/0x30 net/socket.c:1602
>>>  entry_SYSCALL_64_fastpath+0x29/0xa0
>>> RIP: 0033:0x452df9
>>> RSP: 002b:00007f93ec47fc58 EFLAGS: 00000212 ORIG_RAX: 000000000000002a
>>> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452df9
>>> RDX: 000000000000002e RSI: 00000000205fafd2 RDI: 0000000000000018
>>> RBP: 00000000000005a9 R08: 0000000000000000 R09: 0000000000000000
>>> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f6878
>>> R13: 00000000ffffffff R14: 00007f93ec4806d4 R15: 0000000000000000
>>>
>>> Allocated by task 5462:
>>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>>>  set_track mm/kasan/kasan.c:459 [inline]
>>>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>>>  kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3610
>>>  kmalloc include/linux/slab.h:499 [inline]
>>>  kzalloc include/linux/slab.h:688 [inline]
>>>  l2tp_tunnel_create+0x5e1/0x17f0 net/l2tp/l2tp_core.c:1554
>>>  pppol2tp_connect+0x14b7/0x1dd0 net/l2tp/l2tp_ppp.c:707
>>>  SYSC_connect+0x213/0x4a0 net/socket.c:1621
>>>  SyS_connect+0x24/0x30 net/socket.c:1602
>>>  entry_SYSCALL_64_fastpath+0x29/0xa0
>>>
>>> Freed by task 5484:
>>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>>>  set_track mm/kasan/kasan.c:459 [inline]
>>>  kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
>>>  __cache_free mm/slab.c:3488 [inline]
>>>  kfree+0xd6/0x260 mm/slab.c:3803
>>>  __rcu_reclaim kernel/rcu/rcu.h:190 [inline]
>>>  rcu_do_batch kernel/rcu/tree.c:2758 [inline]
>>>  invoke_rcu_callbacks kernel/rcu/tree.c:3012 [inline]
>>>  __rcu_process_callbacks kernel/rcu/tree.c:2979 [inline]
>>>  rcu_process_callbacks+0xe94/0x17f0 kernel/rcu/tree.c:2996
>>>  __do_softirq+0x2d7/0xb85 kernel/softirq.c:285
>>>
>>> The buggy address belongs to the object at ffff8801d80ad780
>>>  which belongs to the cache kmalloc-512 of size 512
>>> The buggy address is located 232 bytes inside of
>>>  512-byte region [ffff8801d80ad780, ffff8801d80ad980)
>>> The buggy address belongs to the page:
>>> page:ffffea0007602b40 count:1 mapcount:0 mapping:ffff8801d80ad000 index:0x0
>>> flags: 0x2fffc0000000100(slab)
>>> raw: 02fffc0000000100 ffff8801d80ad000 0000000000000000 0000000100000006
>>> raw: ffffea00070e8760 ffffea00070f8ca0 ffff8801dac00940 0000000000000000
>>> page dumped because: kasan: bad access detected
>>>
>>> Memory state around the buggy address:
>>>  ffff8801d80ad700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>>  ffff8801d80ad780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>> ffff8801d80ad800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>                                                           ^
>>>  ffff8801d80ad880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>  ffff8801d80ad900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>> ==================================================================
>>>
>>>
>>> ---
>>> This bug is generated by a dumb bot. It may contain errors.
>>> See https://goo.gl/tpsmEJ for details.
>>> Direct all questions to syzkaller@googlegroups.com.
>>>
>>> syzbot will keep track of this bug report.
>>> If you forgot to add the Reported-by tag, once the fix for this bug is
>>> merged
>>> into any tree, please reply to this email with:
>>> #syz fix: exact-commit-title
>>> To mark this as a duplicate of another syzbot report, please reply with:
>>> #syz dup: exact-subject-of-another-report
>>> If it's a one-off invalid bug report, please reply with:
>>> #syz invalid
>>> Note: if the crash happens again, it will cause creation of a new bug
>>> report.
>>> Note: all commands must start from beginning of the line in the email body.
>>>
>>> --
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>
>