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Date:   Wed, 24 Apr 2019 11:09:54 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Stephen Suryaputra <ssuryaextr@...il.com>
Subject: Re: [PATCH net] ipv4: add sanity checks in ipv4_link_failure()

On Wed, Apr 24, 2019 at 11:05 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Before calling __ip_options_compile(), we need to ensure the network
> header is a an IPv4 one, and that it is already pulled in skb->head.
>
> RAW sockets going through a tunnel can end up calling ipv4_link_failure()
> with total garbage in the skb, or arbitrary lengthes.
>
> syzbot report :
>
> BUG: KASAN: stack-out-of-bounds in memcpy include/linux/string.h:355 [inline]
> BUG: KASAN: stack-out-of-bounds in __ip_options_echo+0x294/0x1120 net/ipv4/ip_options.c:123
> Write of size 69 at addr ffff888096abf068 by task syz-executor.4/9204
>
> CPU: 0 PID: 9204 Comm: syz-executor.4 Not tainted 5.1.0-rc5+ #77
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
>  print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
>  kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
>  check_memory_region_inline mm/kasan/generic.c:185 [inline]
>  check_memory_region+0x123/0x190 mm/kasan/generic.c:191
>  memcpy+0x38/0x50 mm/kasan/common.c:133
>  memcpy include/linux/string.h:355 [inline]
>  __ip_options_echo+0x294/0x1120 net/ipv4/ip_options.c:123
>  __icmp_send+0x725/0x1400 net/ipv4/icmp.c:695
>  ipv4_link_failure+0x29f/0x550 net/ipv4/route.c:1204
>  dst_link_failure include/net/dst.h:427 [inline]
[...]
>
> Fixes: ed0de45a1008 ("ipv4: recompile ip options in ipv4_link_failure")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Stephen Suryaputra <ssuryaextr@...il.com>

Acked-by: Willem de Bruijn <willemb@...gle.com>

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