[PATCH] net: handle no dst on skb in icmp6_send

[PATCH] net: handle no dst on skb in icmp6_send

[David Ahern]

Andrey reported the following while fuzzing the kernel with syzkaller:

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 0 PID: 3859 Comm: a.out Not tainted 4.9.0-rc6+ #429
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff8800666d4200 task.stack: ffff880067348000
RIP: 0010:[<ffffffff833617ec>]  [<ffffffff833617ec>]
icmp6_send+0x5fc/0x1e30 net/ipv6/icmp.c:451
RSP: 0018:ffff88006734f2c0  EFLAGS: 00010206
RAX: ffff8800666d4200 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: dffffc0000000000 RDI: 0000000000000018
RBP: ffff88006734f630 R08: ffff880064138418 R09: 0000000000000003
R10: dffffc0000000000 R11: 0000000000000005 R12: 0000000000000000
R13: ffffffff84e7e200 R14: ffff880064138484 R15: ffff8800641383c0
FS:  00007fb3887a07c0(0000) GS:ffff88006cc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 000000006b040000 CR4: 00000000000006f0
Stack:
 ffff8800666d4200 ffff8800666d49f8 ffff8800666d4200 ffffffff84c02460
 ffff8800666d4a1a 1ffff1000ccdaa2f ffff88006734f498 0000000000000046
 ffff88006734f440 ffffffff832f4269 ffff880064ba7456 0000000000000000
Call Trace:
 [<ffffffff83364ddc>] icmpv6_param_prob+0x2c/0x40 net/ipv6/icmp.c:557
 [<     inline     >] ip6_tlvopt_unknown net/ipv6/exthdrs.c:88
 [<ffffffff83394405>] ip6_parse_tlv+0x555/0x670 net/ipv6/exthdrs.c:157
 [<ffffffff8339a759>] ipv6_parse_hopopts+0x199/0x460 net/ipv6/exthdrs.c:663
 [<ffffffff832ee773>] ipv6_rcv+0xfa3/0x1dc0 net/ipv6/ip6_input.c:191
 ...

icmp6_send / icmpv6_send is invoked for both rx and tx paths. In both
cases the dst->dev should be preferred for determining the L3 domain
if the dst has been set on the skb. Fallback to the skb->dev if it has
not. This covers the case reported here where icmp6_send is invoked on
Rx before the route lookup.

Fixes: 5d41ce29e ("net: icmp6_send should use dst dev to determine L3 domain")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
---
 net/ipv6/icmp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 7370ad2e693a..2772004ba5a1 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -447,8 +447,10 @@ static void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
 
 	if (__ipv6_addr_needs_scope_id(addr_type))
 		iif = skb->dev->ifindex;
-	else
-		iif = l3mdev_master_ifindex(skb_dst(skb)->dev);
+	else {
+		dst = skb_dst(skb);
+		iif = l3mdev_master_ifindex(dst ? dst->dev : skb->dev);
+	}
 
 	/*
 	 *	Must not send error if the source does not uniquely
-- 
2.1.4

Re: [PATCH] net: handle no dst on skb in icmp6_send

[David Miller]

From: David Ahern <dsa@cumulusnetworks.com>
Date: Sun, 27 Nov 2016 18:52:53 -0800

> Andrey reported the following while fuzzing the kernel with syzkaller:
 ...
> icmp6_send / icmpv6_send is invoked for both rx and tx paths. In both
> cases the dst->dev should be preferred for determining the L3 domain
> if the dst has been set on the skb. Fallback to the skb->dev if it has
> not. This covers the case reported here where icmp6_send is invoked on
> Rx before the route lookup.
> 
> Fixes: 5d41ce29e ("net: icmp6_send should use dst dev to determine L3 domain")
> Reported-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: David Ahern <dsa@cumulusnetworks.com>

Applied, thanks David.

Re: [PATCH] net: handle no dst on skb in icmp6_send

[Hannes Frederic Sowa]

Hello David,

On Mon, Nov 28, 2016, at 22:13, David Miller wrote:
> From: David Ahern <dsa@cumulusnetworks.com>
> Date: Sun, 27 Nov 2016 18:52:53 -0800
> 
> > Andrey reported the following while fuzzing the kernel with syzkaller:
>  ...
> > icmp6_send / icmpv6_send is invoked for both rx and tx paths. In both
> > cases the dst->dev should be preferred for determining the L3 domain
> > if the dst has been set on the skb. Fallback to the skb->dev if it has
> > not. This covers the case reported here where icmp6_send is invoked on
> > Rx before the route lookup.
> > 
> > Fixes: 5d41ce29e ("net: icmp6_send should use dst dev to determine L3 domain")
> > Reported-by: Andrey Konovalov <andreyknvl@google.com>
> > Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
> 
> Applied, thanks David.

could you queue this patch up for stable. You can remotely kill machines
with this bug.

Thanks,
Hannes

Re: [PATCH] net: handle no dst on skb in icmp6_send

[David Miller]

From: Hannes Frederic Sowa <hannes@stressinduktion.org>
Date: Thu, 08 Dec 2016 15:04:17 +0100

> Hello David,
> 
> On Mon, Nov 28, 2016, at 22:13, David Miller wrote:
>> From: David Ahern <dsa@cumulusnetworks.com>
>> Date: Sun, 27 Nov 2016 18:52:53 -0800
>> 
>> > Andrey reported the following while fuzzing the kernel with syzkaller:
>>  ...
>> > icmp6_send / icmpv6_send is invoked for both rx and tx paths. In both
>> > cases the dst->dev should be preferred for determining the L3 domain
>> > if the dst has been set on the skb. Fallback to the skb->dev if it has
>> > not. This covers the case reported here where icmp6_send is invoked on
>> > Rx before the route lookup.
>> > 
>> > Fixes: 5d41ce29e ("net: icmp6_send should use dst dev to determine L3 domain")
>> > Reported-by: Andrey Konovalov <andreyknvl@google.com>
>> > Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
>> 
>> Applied, thanks David.
> 
> could you queue this patch up for stable. You can remotely kill machines
> with this bug.

Sure, queued up, thanks.