[syzbot] general protection fault in sctp_rcv

[syzbot]

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+581aff...@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]
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


---
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[Xin Long]

On Tue, Sep 21, 2021 at 12:09 PM syzbot
<syzbot+581aff...@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+581aff...@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;

[Dan Carpenter]

The skb_header_pointer() function is annotated as __must_check but that
only means you have to use the return value. These things would be
better as a Coccinelle or Smatch check.

I will create a Smatch warning for this.

regards,
dan carpenter

[Dan Carpenter]

These are the Smatch warnings for this:

net/sctp/input.c:705 sctp_rcv_ootb() error: skb_header_pointer() returns NULL
net/ipv6/netfilter/ip6t_rt.c:111 rt_mt6() error: skb_header_pointer() returns NULL
net/ipv4/icmp.c:1076 icmp_build_probe() error: skb_header_pointer() returns NULL
net/ipv4/icmp.c:1089 icmp_build_probe() error: skb_header_pointer() returns NULL

regards,
dan carpenter

[Xin Long]

Will post follow-ups for rt_mt6() and icmp_build_probe() too.

Thanks!
>
> regards,
> dan carpenter
>