ipv6: fix ip6_tnl_parse_tlv_enc_lim()

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 02923f956ac8ba5f3270e8d5282fd9637c2d278e..ff8ee06491c335d209e86bb15f2526ab1915df3b 100644 (file)
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -400,18 +400,19 @@ 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;
+       unsigned int off = nhoff + 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, off + sizeof(*hdr)))
                        break;
 
-               hdr = (struct ipv6_opt_hdr *) (raw + off);
+               hdr = (struct ipv6_opt_hdr *)(skb->data + off);
                if (nexthdr == NEXTHDR_FRAGMENT) {
                        struct frag_hdr *frag_hdr = (struct frag_hdr *) hdr;
                        if (frag_hdr->frag_off)
@@ -422,20 +423,29 @@ __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, off + optlen))
+                               break;
+
                        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];
+                               tel = (struct ipv6_tlv_tnl_enc_lim *) skb->data + off + i;
                                /* return index of option if found and valid */
                                if (tel->type == IPV6_TLV_TNL_ENCAP_LIMIT &&
                                    tel->length == 1)
-                                       return i;
+                                       return i + off - nhoff;
                                /* else jump to next option */
                                if (tel->type)
                                        i += tel->length + 2;
@@ -443,7 +453,7 @@ __u16 ip6_tnl_parse_tlv_enc_lim(struct sk_buff *skb, __u8 *raw)
                                        i++;
                        }
                }
-               nexthdr = hdr->nexthdr;
+               nexthdr = next;
                off += optlen;
        }
        return 0;