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Commit 84502b5e authored Oct 30, 2013 by Steffen Klassert

xfrm: Fix null pointer dereference when decoding sessions



On some codepaths the skb does not have a dst entry
when xfrm_decode_session() is called. So check for
a valid skb_dst() before dereferencing the device
interface index. We use 0 as the device index if
there is no valid skb_dst(), or at reverse decoding
we use skb_iif as device interface index.

Bug was introduced with git commit bafd4bd4
("xfrm: Decode sessions with output interface.").

Reported-by: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

parent eeb1b733

net/ipv4/xfrm4_policy.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -104,10 +104,14 @@ _decode_session4(struct sk_buff skb, struct flowi fl, int reverse)
		const struct iphdr *iph = ip_hdr(skb);
		u8 xprth = skb_network_header(skb) + iph->ihl 4;
		struct flowi4 *fl4 = &fl->u.ip4;
		int oif = 0;

		if (skb_dst(skb))
		oif = skb_dst(skb)->dev->ifindex;

		memset(fl4, 0, sizeof(struct flowi4));
		fl4->flowi4_mark = skb->mark;
		fl4->flowi4_oif = skb_dst(skb)->dev->ifindex;
		fl4->flowi4_oif = reverse ? skb->skb_iif : oif;

		if (!ip_is_fragment(iph)) {
		switch (iph->protocol) {

net/ipv6/xfrm6_policy.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -135,10 +135,14 @@ _decode_session6(struct sk_buff skb, struct flowi fl, int reverse)
		struct ipv6_opt_hdr *exthdr;
		const unsigned char *nh = skb_network_header(skb);
		u8 nexthdr = nh[IP6CB(skb)->nhoff];
		int oif = 0;

		if (skb_dst(skb))
		oif = skb_dst(skb)->dev->ifindex;

		memset(fl6, 0, sizeof(struct flowi6));
		fl6->flowi6_mark = skb->mark;
		fl6->flowi6_oif = skb_dst(skb)->dev->ifindex;
		fl6->flowi6_oif = reverse ? skb->skb_iif : oif;

		fl6->daddr = reverse ? hdr->saddr : hdr->daddr;
		fl6->saddr = reverse ? hdr->daddr : hdr->saddr;