netdev - [net-next, 1/3] seg6: verify srh pointer in get

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Date:   Wed, 13 Nov 2019 20:29:10 +0100
From:   Andrea Mayer <andrea.mayer@...roma2.it>
To:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Lebrun <dav.lebrun@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Andrea Mayer <andrea.mayer@...roma2.it>
Subject: [net-next, 1/3] seg6: verify srh pointer in get_srh()

pskb_may_pull may change pointers in header. For this reason, it is
mandatory to reload any pointer that points into skb header.

Signed-off-by: Andrea Mayer <andrea.mayer@...roma2.it>
---
 net/ipv6/seg6_local.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
index 9d4f75e0d33a..e187dec2eed1 100644
--- a/net/ipv6/seg6_local.c
+++ b/net/ipv6/seg6_local.c
@@ -75,12 +75,16 @@ static struct ipv6_sr_hdr *get_srh(struct sk_buff *skb)
 		return NULL;
 
 	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
-
 	len = (srh->hdrlen + 1) << 3;
 
 	if (!pskb_may_pull(skb, srhoff + len))
 		return NULL;
 
+	/* note that pskb_may_pull may change pointers in header;
+	 * for this reason it is necessary to reload them when needed.
+	 */
+	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
+
 	if (!seg6_validate_srh(srh, len))
 		return NULL;
 
-- 
2.20.1