[PATCH net 0/2] ipv6: fix ip6_tnl_parse_tlv_enc_lim() issues

[PATCH net 0/2] ipv6: fix ip6_tnl_parse_tlv_enc_lim() issues

[Eric Dumazet]

First patch fixes ip6_tnl_parse_tlv_enc_lim() callers,
bug added in linux-3.7

Second patch fixes ip6_tnl_parse_tlv_enc_lim() itself,
bug predates linux-2.6.12

Based on a report from Dmitry Vyukov, thanks to KASAN.

Eric Dumazet (2):
  ip6_tunnel: must reload ipv6h in ip6ip6_tnl_xmit()
  ipv6: fix ip6_tnl_parse_tlv_enc_lim()

 net/ipv6/ip6_gre.c    |  3 +++
 net/ipv6/ip6_tunnel.c | 34 +++++++++++++++++++++++-----------
 2 files changed, 26 insertions(+), 11 deletions(-)

-- 
2.11.0.483.g087da7b7c-goog

[PATCH net-next 1/2] ip6_tunnel: must reload ipv6h in ip6ip6_tnl_xmit()

[Eric Dumazet]

Since ip6_tnl_parse_tlv_enc_lim() can call pskb_may_pull(),
we must reload any pointer that was related to skb->head
(or skb->data), or risk use after free.

Fixes: c12b395a4664 ("gre: Support GRE over IPv6")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Dmitry Kozlov <xeb@mail.ru>
---
 net/ipv6/ip6_gre.c    | 3 +++
 net/ipv6/ip6_tunnel.c | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 75b6108234dd05a54af0ae51c7c11eaf1ca2..558631860d91bbcb1321a4b566b6e92ddcaf 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -582,6 +582,9 @@ static inline int ip6gre_xmit_ipv6(struct sk_buff *skb, struct net_device *dev)
 		return -1;
 
 	offset = ip6_tnl_parse_tlv_enc_lim(skb, skb_network_header(skb));
+	/* ip6_tnl_parse_tlv_enc_lim() might have reallocated skb->head */
+	ipv6h = ipv6_hdr(skb);
+
 	if (offset > 0) {
 		struct ipv6_tlv_tnl_enc_lim *tel;
 		tel = (struct ipv6_tlv_tnl_enc_lim *)&skb_network_header(skb)[offset];
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 753d6d0860fb14c100ab8b20799782ab8160..02923f956ac8ba5f3270e8d5282fd9637c2d 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1303,6 +1303,8 @@ ip6ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 		fl6.flowlabel = key->label;
 	} else {
 		offset = ip6_tnl_parse_tlv_enc_lim(skb, skb_network_header(skb));
+		/* ip6_tnl_parse_tlv_enc_lim() might have reallocated skb->head */
+		ipv6h = ipv6_hdr(skb);
 		if (offset > 0) {
 			struct ipv6_tlv_tnl_enc_lim *tel;
 
-- 
2.11.0.483.g087da7b7c-goog

[PATCH net-next 2/2] ipv6: fix ip6_tnl_parse_tlv_enc_lim()

[Eric Dumazet]

This function suffers from multiple issues.

First one is that pskb_may_pull() may reallocate skb->head,
so the 'raw' pointer needs either to be reloaded or not used at all.

Second issue is that NEXTHDR_DEST handling does not validate
that the options are present in skb->data, so we might read
garbage or access non existent memory.

With help from Willem de Bruijn.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Willem de Bruijn <willemb@google.com>
---
 net/ipv6/ip6_tunnel.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 02923f956ac8ba5f3270e8d5282fd9637c2d..f9c43c9043f7e386108bca2f2aeb866cfb76 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -400,18 +400,18 @@ ip6_tnl_dev_uninit(struct net_device *dev)
 
 __u16 ip6_tnl_parse_tlv_enc_lim(struct sk_buff *skb, __u8 *raw)
 {
-	const struct ipv6hdr *ipv6h = (const struct ipv6hdr *) raw;
-	__u8 nexthdr = ipv6h->nexthdr;
-	__u16 off = sizeof(*ipv6h);
+	const struct ipv6hdr *ipv6h = (const struct ipv6hdr *)raw;
+	unsigned int nhoff = (raw - skb->data) + sizeof(*ipv6h);
+	u8 next, nexthdr = ipv6h->nexthdr;
 
 	while (ipv6_ext_hdr(nexthdr) && nexthdr != NEXTHDR_NONE) {
-		__u16 optlen = 0;
 		struct ipv6_opt_hdr *hdr;
-		if (raw + off + sizeof(*hdr) > skb->data &&
-		    !pskb_may_pull(skb, raw - skb->data + off + sizeof (*hdr)))
+		u16 optlen;
+
+		if (!pskb_may_pull(skb, nhoff + sizeof(*hdr)))
 			break;
 
-		hdr = (struct ipv6_opt_hdr *) (raw + off);
+		hdr = (struct ipv6_opt_hdr *)(skb->data + nhoff);
 		if (nexthdr == NEXTHDR_FRAGMENT) {
 			struct frag_hdr *frag_hdr = (struct frag_hdr *) hdr;
 			if (frag_hdr->frag_off)
@@ -422,13 +422,23 @@ __u16 ip6_tnl_parse_tlv_enc_lim(struct sk_buff *skb, __u8 *raw)
 		} else {
 			optlen = ipv6_optlen(hdr);
 		}
+		/* cache hdr->nexthdr, since pskb_may_pull() might
+		 * invalidate hdr
+		 */
+		next = hdr->nexthdr;
 		if (nexthdr == NEXTHDR_DEST) {
-			__u16 i = off + 2;
+			u16 i = 2;
+
+			/* Remember : hdr is no longer valid at this point. */
+			if (!pskb_may_pull(skb, nhoff + optlen))
+				break;
+
+			raw = skb->data + nhoff;
 			while (1) {
 				struct ipv6_tlv_tnl_enc_lim *tel;
 
 				/* No more room for encapsulation limit */
-				if (i + sizeof (*tel) > off + optlen)
+				if (i + sizeof(*tel) > optlen)
 					break;
 
 				tel = (struct ipv6_tlv_tnl_enc_lim *) &raw[i];
@@ -443,8 +453,8 @@ __u16 ip6_tnl_parse_tlv_enc_lim(struct sk_buff *skb, __u8 *raw)
 					i++;
 			}
 		}
-		nexthdr = hdr->nexthdr;
-		off += optlen;
+		nexthdr = next;
+		nhoff += optlen;
 	}
 	return 0;
 }
-- 
2.11.0.483.g087da7b7c-goog

Re: [PATCH net-next 2/2] ipv6: fix ip6_tnl_parse_tlv_enc_lim()

[Eric Dumazet]

On Mon, Jan 23, 2017 at 3:58 PM, Eric Dumazet <edumazet@google.com> wrote:
> This function suffers from multiple issues.
>
> First one is that pskb_may_pull() may reallocate skb->head,
> so the 'raw' pointer needs either to be reloaded or not used at all.
>
> Second issue is that NEXTHDR_DEST handling does not validate
> that the options are present in skb->data, so we might read
> garbage or access non existent memory.
>
> With help from Willem de Bruijn.

Hmm, I've added a bug. Will send a V2, sorry for this.