Date:   Thu, 22 Feb 2018 10:50:42 +0100
From:   Xin Long <lucien.xin@...il.com>
To:     syzbot <syzbot+98a809ad0f54884bde26@...kaller.appspotmail.com>
Cc:     davem <davem@...emloft.net>, LKML <linux-kernel@...r.kernel.org>,
        linux-sctp@...r.kernel.org, network dev <netdev@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        syzkaller-bugs@...glegroups.com,
        Vlad Yasevich <vyasevich@...il.com>
Subject: Re: WARNING: refcount bug in sock_wfree

On Wed, Feb 21, 2018 at 9:59 PM, syzbot
<syzbot+98a809ad0f54884bde26@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on upstream commit
> 79c0ef3e85c015b0921a8fd5dd539d1480e9cd6c (Mon Feb 19 19:58:19 2018 +0000)
> Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
>
> So far this crash happened 2 times on
> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/master.
> syzkaller reproducer is attached.
> Raw console output is attached.
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+98a809ad0f54884bde26@...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.
>
> IPv6: ADDRCONF(NETDEV_UP): bridge0: link is not ready
> IPv6: ADDRCONF(NETDEV_UP): bridge0: link is not ready
> audit: type=1400 audit(1519151768.973:11): avc:  denied  { sys_chroot } for
> pid=4169 comm="syz-executor5" capability=18
> scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
> tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns
> permissive=1
> ------------[ cut here ]------------
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 0 PID: 5074 at lib/refcount.c:187
> refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
> Kernel panic - not syncing: panic_on_warn set ...
It seems that we also need to process the chunks in
outqueue->control_chunk_list in sctp_for_each_tx_datachunk()
when peeling off.

>
> CPU: 0 PID: 5074 Comm: syz-executor5 Not tainted 4.16.0-rc2+ #322
> 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
>  panic+0x1e4/0x41c kernel/panic.c:183
>  __warn+0x1dc/0x200 kernel/panic.c:547
>  report_bug+0x211/0x2d0 lib/bug.c:184
>  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
>  fixup_bug arch/x86/kernel/traps.c:247 [inline]
>  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>  invalid_op+0x58/0x80 arch/x86/entry/entry_64.S:957
> RIP: 0010:refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
> RSP: 0018:ffff8801cf2b6490 EFLAGS: 00010282
> RAX: dffffc0000000008 RBX: 0000000000000401 RCX: ffffffff815abdbe
> RDX: 0000000000000000 RSI: 1ffff10039e56c42 RDI: 1ffff10039e56c17
> RBP: ffff8801cf2b6520 R08: 1ffff10039e56bd9 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff10039e56c93
> R13: 00000000ffffff01 R14: 0000000000000500 R15: ffff8801ae3c69fc
>  sock_wfree+0xa6/0x140 net/core/sock.c:1819
>  sctp_wfree+0x2eb/0x670 net/sctp/socket.c:8065
>  skb_release_head_state+0x124/0x260 net/core/skbuff.c:612
>  skb_release_all+0x15/0x60 net/core/skbuff.c:625
>  __kfree_skb net/core/skbuff.c:641 [inline]
>  consume_skb+0x153/0x490 net/core/skbuff.c:701
>  sctp_chunk_destroy net/sctp/sm_make_chunk.c:1450 [inline]
>  sctp_chunk_put+0x29c/0x420 net/sctp/sm_make_chunk.c:1477
>  sctp_chunk_free+0x53/0x60 net/sctp/sm_make_chunk.c:1464
>  __sctp_outq_teardown+0x244/0x1230 net/sctp/outqueue.c:234
>  sctp_outq_free+0x15/0x20 net/sctp/outqueue.c:291
>  sctp_association_free+0x2d0/0x930 net/sctp/associola.c:356
>  sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:939 [inline]
>  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1343 [inline]
>  sctp_side_effects net/sctp/sm_sideeffect.c:1210 [inline]
>  sctp_do_sm+0x32e3/0x6ed0 net/sctp/sm_sideeffect.c:1181
>  sctp_primitive_ABORT+0xa0/0xd0 net/sctp/primitive.c:119
>  sctp_close+0x266/0x9a0 net/sctp/socket.c:1539
>  inet_release+0xed/0x1c0 net/ipv4/af_inet.c:427
>  sock_release+0x8d/0x1e0 net/socket.c:595
>  sock_close+0x16/0x20 net/socket.c:1149
>  __fput+0x327/0x7e0 fs/file_table.c:209
>  ____fput+0x15/0x20 fs/file_table.c:243
>  task_work_run+0x199/0x270 kernel/task_work.c:113
>  exit_task_work include/linux/task_work.h:22 [inline]
>  do_exit+0x9bb/0x1ad0 kernel/exit.c:865
>  do_group_exit+0x149/0x400 kernel/exit.c:968
>  get_signal+0x73a/0x16d0 kernel/signal.c:2469
>  do_signal+0x90/0x1e90 arch/x86/kernel/signal.c:809
>  exit_to_usermode_loop+0x258/0x2f0 arch/x86/entry/common.c:162
>  prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
>  syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
>  do_syscall_64+0x6e5/0x940 arch/x86/entry/common.c:292
>  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> RIP: 0033:0x453da9
> RSP: 002b:00007f297546ace8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> RAX: fffffffffffffe00 RBX: 000000000072bf80 RCX: 0000000000453da9
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000072bf80
> RBP: 000000000072bf80 R08: 0000000000000000 R09: 000000000072bf58
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000a3e8ef R14: 00007f297546b9c0 R15: 0000000000000001
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
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>
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