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Date:   Fri, 20 Jul 2018 08:53:04 +0100
From:   James Chapman <jchapman@...alix.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        g.nault@...halink.fr, Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        syzbot <syzbot+065d0fc357520c8f6039@...kaller.appspotmail.com>,
        Guillaume Nault <g.nault@...halink.fr>
Subject: Re: KASAN: use-after-free Read in l2tp_session_create

On 18/07/18 12:00, Dmitry Vyukov wrote:
> On Tue, Jan 16, 2018 at 7:29 PM, syzbot
> <syzbot+065d0fc357520c8f6039@...kaller.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@...kaller.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
>
>
>> ==================================================================
>> 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@...glegroups.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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>> To view this discussion on the web visit
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