netdev - Re: [PATCH net 0/8] net: fix uninit-values in networking stack

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Message-ID: <0a539248-4e45-a429-f708-d906c145c736@gmail.com>
Date:   Sun, 8 Apr 2018 09:55:58 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     edumazet@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net 0/8] net: fix uninit-values in networking stack



On 04/08/2018 09:49 AM, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Sun, 8 Apr 2018 09:38:13 -0700
> 
>> On 04/07/2018 07:40 PM, David Miller wrote:
>>> From: Eric Dumazet <edumazet@...gle.com>
>>> Date: Sat,  7 Apr 2018 13:42:35 -0700
>>>
>>>> It seems syzbot got new features enabled, and fired some interesting
>>>> reports. Oh well.
>>>
>>> Series applied, however in patch #7 the condition syzbot detects
>>> cannot happen.
>>>
>>> In all code paths that lead to __mkroute_output() with res->type
>>> uninitialized, __mkroute_output() will reassign the local variable
>>> 'type' before reading it.
>>
>> Well, we have :
>>
>> u16 type = res->type;
>> ...
>>
>>        if (ipv4_is_lbcast(fl4->daddr))
>>                 type = RTN_BROADCAST;
>>         else if (ipv4_is_multicast(fl4->daddr))
>>                 type = RTN_MULTICAST;
>>         else if (ipv4_is_zeronet(fl4->daddr))
>>                 return ERR_PTR(-EINVAL);
>>
>> ...
>>
>> if (type == RTN_BROADCAST) {  /* This is where KMSAN complained */
>>
>> So it looks like type could have been random at this point.
> 
> Ok, then.  It seems that the requirement is:
> 
> 	fl4->flowi4_oif is non-zero
> 	fl4->daddr is neither local multicast nor lbcast
> 	fl4->flowi4_proto is IPPROTO_IGMP
> 
> Then we can trigger such a sequence of events.
> 

OK, maybe some more work then ;)


I also have a report of a WARN() in ip_rt_bug(), added in commit c378a9c019cf5e017d1ed24954b54fae7bebd2bc
by Dave Jones.

Not sure what to do, maybe revert, since ip_rt_bug() is not catastrophic.

WARNING: CPU: 0 PID: 11678 at net/ipv4/route.c:1213 ip_rt_bug+0x15/0x20 net/ipv4/route.c:1212
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 11678 Comm: kworker/u4:7 Not tainted 4.16.0-rc6+ #289
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 panic+0x1e4/0x41c kernel/panic.c:183
 __warn+0x1dc/0x200 kernel/panic.c:547
 report_bug+0x1f4/0x2b0 lib/bug.c:186
 fixup_bug.part.10+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+0x1b/0x40 arch/x86/entry/entry_64.S:986
RIP: 0010:ip_rt_bug+0x15/0x20 net/ipv4/route.c:1212
RSP: 0018:ffff8801db007290 EFLAGS: 00010282
RAX: dffffc0000000000 RBX: ffff8801d8dda3c0 RCX: ffffffff856c31ca
RDX: 0000000000000100 RSI: ffffffff8858c300 RDI: 0000000000000282
RBP: ffff8801db007298 R08: 1ffff1003b600de1 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801d8dda3c0
R13: ffff88019bdb2200 R14: ffff88019bdeed80 R15: ffff8801d8dda418
 dst_output include/net/dst.h:444 [inline]
 ip_local_out+0x95/0x160 net/ipv4/ip_output.c:124
 ip_send_skb+0x3c/0xc0 net/ipv4/ip_output.c:1414
 ip_push_pending_frames+0x64/0x80 net/ipv4/ip_output.c:1434
 icmp_push_reply+0x395/0x4f0 net/ipv4/icmp.c:394
 icmp_send+0x1136/0x19b0 net/ipv4/icmp.c:741
 ipv4_link_failure+0x2a/0x1b0 net/ipv4/route.c:1200
 dst_link_failure include/net/dst.h:427 [inline]
 arp_error_report+0xae/0x180 net/ipv4/arp.c:297
 neigh_invalidate+0x225/0x530 net/core/neighbour.c:883
 neigh_timer_handler+0x897/0xd60 net/core/neighbour.c:969
 call_timer_fn+0x228/0x820 kernel/time/timer.c:1326
 expire_timers kernel/time/timer.c:1363 [inline]
 __run_timers+0x7ee/0xb70 kernel/time/timer.c:1666
 run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285
 invoke_softirq kernel/softirq.c:365 [inline]
 irq_exit+0x1cc/0x200 kernel/softirq.c:405
 exiting_irq arch/x86/include/asm/apic.h:541 [inline]
 smp_apic_timer_interrupt+0x16b/0x700 arch/x86/kernel/apic/apic.c:1052
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:857
 </IRQ>