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>

1 files changed, 15 insertions, 65 deletions

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 13ef5bc05cf..578f3c1a16d 100644
--- 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;
 }