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From:   Xin Long <lucien.xin@gmail.com>
Date:   Sat, 10 Feb 2018 19:17:52 +0800
Message-ID: <CADvbK_d9Z3OsHnLc2mg-3e=0t6sVFnEVXoDah3nWJrFSyaq+5w@mail.gmail.com>
Subject: Re: kernel BUG at net/core/skbuff.c:LINE! (3)
To:     syzbot <syzbot+b2bf2652983d23734c5c@syzkaller.appspotmail.com>
Cc:     davem <davem@davemloft.net>, LKML <linux-kernel@vger.kernel.org>,
        linux-sctp@vger.kernel.org, network dev <netdev@vger.kernel.org>,
        Neil Horman <nhorman@tuxdriver.com>,
        syzkaller-bugs@googlegroups.com,
        Vlad Yasevich <vyasevich@gmail.com>
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On Fri, Feb 2, 2018 at 3:21 AM, syzbot
<syzbot+b2bf2652983d23734c5c@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on net-next commit
> b2fe5fa68642860e7de76167c3111623aa0d5de1 (Wed Jan 31 22:31:10 2018 +0000)
> Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
>
> Unfortunately, I don't have any reproducer for this crash yet.
> 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+b2bf2652983d23734c5c@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.
>
> skbuff: skb_over_panic: text:000000004b89f3be len:66136 put:66124
> head:00000000f255561a data:00000000ccb55e52 tail:0x10310 end:0x6c0
> dev:<NULL>
From the raw log, it should be a data chunk.
But I couldn't see how len:66136 happened?
considering that frag_point is always smaller than SCTP_MAX_CHUNK_LEN.

> ------------[ cut here ]------------
> kernel BUG at net/core/skbuff.c:104!
> invalid opcode: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 1 PID: 19738 Comm: syz-executor3 Not tainted 4.15.0+ #219
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:skb_panic+0x162/0x1f0 net/core/skbuff.c:100
> RSP: 0018:ffff8801c1a6e4e8 EFLAGS: 00010286
> RAX: 000000000000008f RBX: ffff8801d0090000 RCX: 0000000000000000
> RDX: 000000000000008f RSI: ffffc90003d53000 RDI: ffffed003834dc91
> RBP: ffff8801c1a6e550 R08: 1ffff1003834dc1f R09: 0000000000000000
> R10: 0000000000000004 R11: 0000000000000000 R12: ffffffff863fe4e0
> R13: ffffffff85276640 R14: 000000000001024c R15: ffffffff863fdd20
> FS:  00007f69cd01b700(0000) GS:ffff8801db500000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000718008 CR3: 00000001c71c7006 CR4: 00000000001606e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  skb_over_panic net/core/skbuff.c:109 [inline]
>  skb_put+0x18d/0x1d0 net/core/skbuff.c:1695
>  skb_put_data include/linux/skbuff.h:2049 [inline]
>  sctp_packet_pack net/sctp/output.c:473 [inline]
>  sctp_packet_transmit+0x1180/0x3750 net/sctp/output.c:606
>  sctp_outq_flush+0x121b/0x4060 net/sctp/outqueue.c:1197
>  sctp_outq_uncork+0x5a/0x70 net/sctp/outqueue.c:776
>  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1807 [inline]
>  sctp_side_effects net/sctp/sm_sideeffect.c:1210 [inline]
>  sctp_do_sm+0x4e0/0x6ed0 net/sctp/sm_sideeffect.c:1181
>  sctp_primitive_SEND+0xa0/0xd0 net/sctp/primitive.c:178
>  sctp_sendmsg+0x1894/0x35e0 net/sctp/socket.c:2029
>  inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:764
>  sock_sendmsg_nosec net/socket.c:630 [inline]
>  sock_sendmsg+0xca/0x110 net/socket.c:640
>  sock_write_iter+0x31a/0x5d0 net/socket.c:909
>  call_write_iter include/linux/fs.h:1781 [inline]
>  do_iter_readv_writev+0x55c/0x830 fs/read_write.c:653
>  do_iter_write+0x154/0x540 fs/read_write.c:932
>  vfs_writev+0x18a/0x340 fs/read_write.c:977
>  do_writev+0xfc/0x2a0 fs/read_write.c:1012
>  SYSC_writev fs/read_write.c:1085 [inline]
>  SyS_writev+0x27/0x30 fs/read_write.c:1082
>  entry_SYSCALL_64_fastpath+0x29/0xa0
> RIP: 0033:0x453299
> RSP: 002b:00007f69cd01ac58 EFLAGS: 00000212 ORIG_RAX: 0000000000000014
> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000453299
> RDX: 0000000000000001 RSI: 0000000020f7ffe0 RDI: 0000000000000013
> RBP: 00000000000005c5 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f7b18
> R13: 00000000ffffffff R14: 00007f69cd01b6d4 R15: 0000000000000000
> Code: 04 01 84 c0 74 04 3c 03 7e 23 8b 8b 80 00 00 00 41 57 48 c7 c7 60 dd
> 3f 86 52 56 4c 89 ea 41 50 4c 89 e6 45 89 f0 e8 c6 d7 25 fd <0f> 0b 4c 89 4d
> b8 4c 89 45 c0 48 89 75 c8 48 89 55 d0 e8 47 53
> RIP: skb_panic+0x162/0x1f0 net/core/skbuff.c:100 RSP: ffff8801c1a6e4e8
> ---[ end trace c7cd29819a9b12ab ]---
>
>
> ---
> 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.
>
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