Patchwork [net-next] ip_gre: fix a possible crash in parse_gre_header()

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Submitter Eric Dumazet
Date April 5, 2013, 1:41 a.m.
Message ID <1365126087.3308.17.camel@edumazet-glaptop>
Download mbox | patch
Permalink /patch/234013/
State Accepted
Delegated to: David Miller
Headers show

Comments

Eric Dumazet - April 5, 2013, 1:41 a.m.
From: Eric Dumazet <edumazet@google.com>

pskb_may_pull() can change skb->head, so we must init iph/greh after
calling it.

Bug added in commit c54419321455 (GRE: Refactor GRE tunneling code.)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Pravin B Shelar <pshelar@nicira.com>
---
 net/ipv4/ip_gre.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)



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David Miller - April 8, 2013, 4:01 p.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 04 Apr 2013 18:41:27 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> pskb_may_pull() can change skb->head, so we must init iph/greh after
> calling it.
> 
> Bug added in commit c54419321455 (GRE: Refactor GRE tunneling code.)
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied.
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Patch

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index e5dfd28..987a4e5 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -159,14 +159,14 @@  static int ip_gre_calc_hlen(__be16 o_flags)
 static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 			    bool *csum_err, int *hdr_len)
 {
-	struct iphdr *iph = ip_hdr(skb);
-	struct gre_base_hdr *greh;
+	unsigned int ip_hlen = ip_hdrlen(skb);
+	const struct gre_base_hdr *greh;
 	__be32 *options;
 
 	if (unlikely(!pskb_may_pull(skb, sizeof(struct gre_base_hdr))))
 		return -EINVAL;
 
-	greh = (struct gre_base_hdr *)((u8 *)iph + (iph->ihl << 2));
+	greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
 	if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
 		return -EINVAL;
 
@@ -176,6 +176,8 @@  static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	if (!pskb_may_pull(skb, *hdr_len))
 		return -EINVAL;
 
+	greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
+
 	tpi->proto = greh->protocol;
 
 	options = (__be32 *)(greh + 1);