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

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Message-Id: <20180326150807.68287-1-edumazet@google.com>
Date:   Mon, 26 Mar 2018 08:08:07 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Pravin B Shelar <pshelar@....org>
Subject: [PATCH net] net: fix possible out-of-bound read in skb_network_protocol()

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;
 	}
 
-- 
2.17.0.rc0.231.g781580f067-goog