netdev - [PATCH net] net: __skb_flow_dissect() must cap its return value

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Date:   Wed, 09 Nov 2016 16:04:46 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Yibin Yang <yibyang@...co.com>, Tom Herbert <tom@...bertland.com>,
        Jojy Varghese <jojvargh@...co.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        netdev <netdev@...r.kernel.org>
Subject: [PATCH net] net: __skb_flow_dissect() must cap its return value

From: Eric Dumazet <edumazet@...gle.com>

After Tom patch, thoff field could point past the end of the buffer,
this could fool some callers.

If an skb was provided, skb->len should be the upper limit.
If not, hlen is supposed to be the upper limit.

Fixes: a6e544b0a88b ("flow_dissector: Jump to exit code in __skb_flow_dissect")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Yibin Yang <yibyang@...co.com
Acked-by: Alexander Duyck <alexander.h.duyck@...el.com>
Acked-by: Willem de Bruijn <willemb@...gle.com>
Acked-by: Alexei Starovoitov <ast@...nel.org>
---
 net/core/flow_dissector.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 44e6ba9d3a6b..5a908c534bec 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -122,7 +122,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 	struct flow_dissector_key_keyid *key_keyid;
 	bool skip_vlan = false;
 	u8 ip_proto = 0;
-	bool ret = false;
+	bool ret;
 
 	if (!data) {
 		data = skb->data;
@@ -549,12 +549,17 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 out_good:
 	ret = true;
 
-out_bad:
+	key_control->thoff = (u16)nhoff;
+out:
 	key_basic->n_proto = proto;
 	key_basic->ip_proto = ip_proto;
-	key_control->thoff = (u16)nhoff;
 
 	return ret;
+
+out_bad:
+	ret = false;
+	key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen);
+	goto out;
 }
 EXPORT_SYMBOL(__skb_flow_dissect);