netfilter: discard overlapping IPv6 fragment

RFC5722 prohibits reassembling IPv6 fragments when some data overlaps.

Bug spotted by Zhang Zuotao <zuotao.zhang@6wind.com>.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 13ef5bc05cf5220a3e2aa62543c4a12b79e5a98a..578f3c1a16db614614f986947cbae5a7960fcdb5 100644 (file)
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -113,14 +113,6 @@ static void nf_skb_free(struct sk_buff *skb)
                kfree_skb(NFCT_FRAG6_CB(skb)->orig);
 }
 
-/* Memory Tracking Functions. */
-static void frag_kfree_skb(struct sk_buff *skb)
-{
-       atomic_sub(skb->truesize, &nf_init_frags.mem);
-       nf_skb_free(skb);
-       kfree_skb(skb);
-}
-
 /* Destruction primitives. */
 
 static __inline__ void fq_put(struct nf_ct_frag6_queue *fq)
@@ -282,66 +274,22 @@ static int nf_ct_frag6_queue(struct nf_ct_frag6_queue *fq, struct sk_buff *skb,
        }
 
 found:
-       /* We found where to put this one.  Check for overlap with
-        * preceding fragment, and, if needed, align things so that
-        * any overlaps are eliminated.
-        */
-       if (prev) {
-               int i = (NFCT_FRAG6_CB(prev)->offset + prev->len) - offset;
-
-               if (i > 0) {
-                       offset += i;
-                       if (end <= offset) {
-                               pr_debug("overlap\n");
-                               goto err;
-                       }
-                       if (!pskb_pull(skb, i)) {
-                               pr_debug("Can't pull\n");
-                               goto err;
-                       }
-                       if (skb->ip_summed != CHECKSUM_UNNECESSARY)
-                               skb->ip_summed = CHECKSUM_NONE;
-               }
-       }
-
-       /* Look for overlap with succeeding segments.
-        * If we can merge fragments, do it.
+       /* RFC5722, Section 4:
+        *                                  When reassembling an IPv6 datagram, if
+        *   one or more its constituent fragments is determined to be an
+        *   overlapping fragment, the entire datagram (and any constituent
+        *   fragments, including those not yet received) MUST be silently
+        *   discarded.
         */
-       while (next && NFCT_FRAG6_CB(next)->offset < end) {
-               /* overlap is 'i' bytes */
-               int i = end - NFCT_FRAG6_CB(next)->offset;
-
-               if (i < next->len) {
-                       /* Eat head of the next overlapped fragment
-                        * and leave the loop. The next ones cannot overlap.
-                        */
-                       pr_debug("Eat head of the overlapped parts.: %d", i);
-                       if (!pskb_pull(next, i))
-                               goto err;
 
-                       /* next fragment */
-                       NFCT_FRAG6_CB(next)->offset += i;
-                       fq->q.meat -= i;
-                       if (next->ip_summed != CHECKSUM_UNNECESSARY)
-                               next->ip_summed = CHECKSUM_NONE;
-                       break;
-               } else {
-                       struct sk_buff *free_it = next;
-
-                       /* Old fragmnet is completely overridden with
-                        * new one drop it.
-                        */
-                       next = next->next;
+       /* Check for overlap with preceding fragment. */
+       if (prev &&
+           (NFCT_FRAG6_CB(prev)->offset + prev->len) - offset > 0)
+               goto discard_fq;
 
-                       if (prev)
-                               prev->next = next;
-                       else
-                               fq->q.fragments = next;
-
-                       fq->q.meat -= free_it->len;
-                       frag_kfree_skb(free_it);
-               }
-       }
+       /* Look for overlap with succeeding segment. */
+       if (next && NFCT_FRAG6_CB(next)->offset < end)
+               goto discard_fq;
 
        NFCT_FRAG6_CB(skb)->offset = offset;
 
@@ -371,6 +319,8 @@ found:
        write_unlock(&nf_frags.lock);
        return 0;
 
+discard_fq:
+       fq_kill(fq);
 err:
        return -1;
 }