linux-kernel - [PATCH 5.4 23/37] gre: refetch erspan header from skb->data after pskb_may

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Date:   Tue, 17 Dec 2019 21:09:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        William Tu <u9012063@...il.com>,
        Simon Horman <simon.horman@...ronome.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.4 23/37] gre: refetch erspan header from skb->data after pskb_may_pull()

From: Cong Wang <xiyou.wangcong@...il.com>

[ Upstream commit 0e4940928c26527ce8f97237fef4c8a91cd34207 ]

After pskb_may_pull() we should always refetch the header
pointers from the skb->data in case it got reallocated.

In gre_parse_header(), the erspan header is still fetched
from the 'options' pointer which is fetched before
pskb_may_pull().

Found this during code review of a KMSAN bug report.

Fixes: cb73ee40b1b3 ("net: ip_gre: use erspan key field for tunnel lookup")
Cc: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Acked-by: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Acked-by: William Tu <u9012063@...il.com>
Reviewed-by: Simon Horman <simon.horman@...ronome.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/gre_demux.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c
@@ -127,7 +127,7 @@ int gre_parse_header(struct sk_buff *skb
 		if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
 			return -EINVAL;
 
-		ershdr = (struct erspan_base_hdr *)options;
+		ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
 		tpi->key = cpu_to_be32(get_session_id(ershdr));
 	}