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From:   Xin Long <lucien.xin@gmail.com>
Date:   Wed, 22 Sep 2021 17:18:29 +0800
Message-ID: <CADvbK_c-V6orWGm2ae1pxoUU-5J-1J-a057hYemA6oTESGhFMg@mail.gmail.com>
Subject: Re: [syzbot] general protection fault in sctp_rcv
To:     syzbot <syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com>
Cc:     davem <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "linux-sctp @ vger . kernel . org" <linux-sctp@vger.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        network dev <netdev@vger.kernel.org>,
        Neil Horman <nhorman@tuxdriver.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Vlad Yasevich <vyasevich@gmail.com>
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On Tue, Sep 21, 2021 at 12:09 PM syzbot
<syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    98dc68f8b0c2 selftests: nci: replace unsigned int with int
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=11fd443d300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c31c0936547df9ea
> dashboard link: https://syzkaller.appspot.com/bug?extid=581aff2ae6b860625116
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com
>
> general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 0 PID: 11205 Comm: kworker/0:12 Not tainted 5.14.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: ipv6_addrconf addrconf_dad_work
> RIP: 0010:sctp_rcv_ootb net/sctp/input.c:705 [inline]
by anyway, checking if skb_header_pointer() return NULL is always needed:
@@ -702,7 +702,7 @@ static int sctp_rcv_ootb(struct sk_buff *skb)
                ch = skb_header_pointer(skb, offset, sizeof(*ch), &_ch);

                /* Break out if chunk length is less then minimal. */
-               if (ntohs(ch->length) < sizeof(_ch))
+               if (!ch || ntohs(ch->length) < sizeof(_ch))
                        break;

> RIP: 0010:sctp_rcv+0x1d84/0x3220 net/sctp/input.c:196
> Code: fb 03 0f 8e 51 01 00 00 e8 99 ac 17 f9 4c 01 ed e8 91 ac 17 f9 48 8d 7d 02 48 b9 00 00 00 00 00 fc ff df 48 89 f8 48 c1 e8 03 <0f> b6 14 08 48 89 f8 83 e0 07 83 c0 01 38 d0 7c 08 84 d2 0f 85 ea
> RSP: 0018:ffffc900000079c8 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: 00000000fffffff2 RCX: dffffc0000000000
> RDX: ffff88803d790000 RSI: ffffffff885e62cf RDI: 0000000000000002
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffff885e6448 R11: 0000000000000000 R12: 000000000000050c
> R13: ffff88803f42a0e4 R14: 0000000000000510 R15: ffff888070e2c500
> FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f0dce1763ad CR3: 0000000027250000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <IRQ>
>  sctp6_rcv+0x38/0x60 net/sctp/ipv6.c:1109
>  ip6_protocol_deliver_rcu+0x2e9/0x1ca0 net/ipv6/ip6_input.c:422
>  ip6_input_finish+0x62/0x170 net/ipv6/ip6_input.c:463
>  NF_HOOK include/linux/netfilter.h:307 [inline]
>  NF_HOOK include/linux/netfilter.h:301 [inline]
>  ip6_input+0x9c/0xd0 net/ipv6/ip6_input.c:472
>  dst_input include/net/dst.h:460 [inline]
>  ip6_rcv_finish net/ipv6/ip6_input.c:76 [inline]
>  NF_HOOK include/linux/netfilter.h:307 [inline]
>  NF_HOOK include/linux/netfilter.h:301 [inline]
>  ipv6_rcv+0x28c/0x3c0 net/ipv6/ip6_input.c:297
>  __netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:5436
>  __netif_receive_skb+0x24/0x1b0 net/core/dev.c:5550
>  process_backlog+0x2a5/0x6c0 net/core/dev.c:6427
>  __napi_poll+0xaf/0x440 net/core/dev.c:6982
>  napi_poll net/core/dev.c:7049 [inline]
>  net_rx_action+0x801/0xb40 net/core/dev.c:7136
>  __do_softirq+0x29b/0x9c2 kernel/softirq.c:558
>  do_softirq.part.0+0xde/0x130 kernel/softirq.c:459
>  </IRQ>
>  do_softirq kernel/softirq.c:451 [inline]
>  __local_bh_enable_ip+0x102/0x120 kernel/softirq.c:383
>  spin_unlock_bh include/linux/spinlock.h:408 [inline]
>  addrconf_dad_work+0x474/0x1340 net/ipv6/addrconf.c:4077
>  process_one_work+0x9bf/0x16b0 kernel/workqueue.c:2297
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
>  kthread+0x3e5/0x4d0 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> Modules linked in:
> ---[ end trace 80d76c5102c944b0 ]---
> RIP: 0010:sctp_rcv_ootb net/sctp/input.c:705 [inline]
> RIP: 0010:sctp_rcv+0x1d84/0x3220 net/sctp/input.c:196
> Code: fb 03 0f 8e 51 01 00 00 e8 99 ac 17 f9 4c 01 ed e8 91 ac 17 f9 48 8d 7d 02 48 b9 00 00 00 00 00 fc ff df 48 89 f8 48 c1 e8 03 <0f> b6 14 08 48 89 f8 83 e0 07 83 c0 01 38 d0 7c 08 84 d2 0f 85 ea
> RSP: 0018:ffffc900000079c8 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: 00000000fffffff2 RCX: dffffc0000000000
> RDX: ffff88803d790000 RSI: ffffffff885e62cf RDI: 0000000000000002
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffff885e6448 R11: 0000000000000000 R12: 000000000000050c
> R13: ffff88803f42a0e4 R14: 0000000000000510 R15: ffff888070e2c500
> FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f0dce1763ad CR3: 0000000027250000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:   fb                      sti
>    1:   03 0f                   add    (%rdi),%ecx
>    3:   8e 51 01                mov    0x1(%rcx),%ss
>    6:   00 00                   add    %al,(%rax)
>    8:   e8 99 ac 17 f9          callq  0xf917aca6
>    d:   4c 01 ed                add    %r13,%rbp
>   10:   e8 91 ac 17 f9          callq  0xf917aca6
>   15:   48 8d 7d 02             lea    0x2(%rbp),%rdi
>   19:   48 b9 00 00 00 00 00    movabs $0xdffffc0000000000,%rcx
>   20:   fc ff df
>   23:   48 89 f8                mov    %rdi,%rax
>   26:   48 c1 e8 03             shr    $0x3,%rax
> * 2a:   0f b6 14 08             movzbl (%rax,%rcx,1),%edx <-- trapping instruction
>   2e:   48 89 f8                mov    %rdi,%rax
>   31:   83 e0 07                and    $0x7,%eax
>   34:   83 c0 01                add    $0x1,%eax
>   37:   38 d0                   cmp    %dl,%al
>   39:   7c 08                   jl     0x43
>   3b:   84 d2                   test   %dl,%dl
>   3d:   0f                      .byte 0xf
>   3e:   85 ea                   test   %ebp,%edx
>
>
> ---
> This report 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@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.