netdev - Re: [PATCH net] net: fix possible out-of-bound read in skb_network

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Date:   Mon, 26 Mar 2018 19:19:42 -0700
From:   Pravin Shelar <pshelar@....org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net] net: fix possible out-of-bound read in skb_network_protocol()

On Mon, Mar 26, 2018 at 8:08 AM, Eric Dumazet <edumazet@...gle.com> wrote:
> skb mac header is not necessarily set at the time skb_network_protocol()
> is called. Use skb->data instead.
>
> BUG: KASAN: slab-out-of-bounds in skb_network_protocol+0x46b/0x4b0 net/core/dev.c:2739
> Read of size 2 at addr ffff8801b3097a0b by task syz-executor5/14242
>
> CPU: 1 PID: 14242 Comm: syz-executor5 Not tainted 4.16.0-rc6+ #280
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x24d lib/dump_stack.c:53
>  print_address_description+0x73/0x250 mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report+0x23c/0x360 mm/kasan/report.c:412
>  __asan_report_load_n_noabort+0xf/0x20 mm/kasan/report.c:443
>  skb_network_protocol+0x46b/0x4b0 net/core/dev.c:2739
>  harmonize_features net/core/dev.c:2924 [inline]
>  netif_skb_features+0x509/0x9b0 net/core/dev.c:3011
>  validate_xmit_skb+0x81/0xb00 net/core/dev.c:3084
>  validate_xmit_skb_list+0xbf/0x120 net/core/dev.c:3142
>  packet_direct_xmit+0x117/0x790 net/packet/af_packet.c:256
>  packet_snd net/packet/af_packet.c:2944 [inline]
>  packet_sendmsg+0x3aed/0x60b0 net/packet/af_packet.c:2969
>  sock_sendmsg_nosec net/socket.c:629 [inline]
>  sock_sendmsg+0xca/0x110 net/socket.c:639
>  ___sys_sendmsg+0x767/0x8b0 net/socket.c:2047
>  __sys_sendmsg+0xe5/0x210 net/socket.c:2081
>
> Fixes: 19acc327258a ("gso: Handle Trans-Ether-Bridging protocol in skb_network_protocol()")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Pravin B Shelar <pshelar@....org>
> Reported-by: Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
>  net/core/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 12be205357146f0dcd55cc6e6f71dfb65fdeb33b..ef0cc6ea5f8da5b87c751d9eebfc0943fbe36a06 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2735,7 +2735,7 @@ __be16 skb_network_protocol(struct sk_buff *skb, int *depth)
>                 if (unlikely(!pskb_may_pull(skb, sizeof(struct ethhdr))))
>                         return 0;
>
> -               eth = (struct ethhdr *)skb_mac_header(skb);
> +               eth = (struct ethhdr *)skb->data;
>                 type = eth->h_proto;
>         }
>
Thanks for fixing it.