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Subject[ 167/184] ipv6: discard overlapping fragment
2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolas Dichtel <nicolas.dichtel@6wind.com>

commit 70789d7052239992824628db8133de08dc78e593 upstream

RFC5722 prohibits reassembling 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>
[dannf: backported to Debian's 2.6.32]
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
net/ipv6/reassembly.c | 74 +++++++++++----------------------------------------
1 file changed, 15 insertions(+), 59 deletions(-)

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 4d18699..105de22 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -148,16 +148,6 @@ int ip6_frag_match(struct inet_frag_queue *q, void *a)
}
EXPORT_SYMBOL(ip6_frag_match);

-/* Memory Tracking Functions. */
-static inline void frag_kfree_skb(struct netns_frags *nf,
- struct sk_buff *skb, int *work)
-{
- if (work)
- *work -= skb->truesize;
- atomic_sub(skb->truesize, &nf->mem);
- kfree_skb(skb);
-}
-
void ip6_frag_init(struct inet_frag_queue *q, void *a)
{
struct frag_queue *fq = container_of(q, struct frag_queue, q);
@@ -348,58 +338,22 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
prev = next;
}

- /* We found where to put this one. Check for overlap with
- * preceding fragment, and, if needed, align things so that
- * any overlaps are eliminated.
+ /* 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.
*/
- if (prev) {
- int i = (FRAG6_CB(prev)->offset + prev->len) - offset;

- if (i > 0) {
- offset += i;
- if (end <= offset)
- goto err;
- if (!pskb_pull(skb, i))
- goto err;
- if (skb->ip_summed != CHECKSUM_UNNECESSARY)
- skb->ip_summed = CHECKSUM_NONE;
- }
- }
+ /* Check for overlap with preceding fragment. */
+ if (prev &&
+ (FRAG6_CB(prev)->offset + prev->len) - offset > 0)
+ goto discard_fq;

- /* Look for overlap with succeeding segments.
- * If we can merge fragments, do it.
- */
- while (next && FRAG6_CB(next)->offset < end) {
- int i = end - FRAG6_CB(next)->offset; /* overlap is 'i' bytes */
-
- if (i < next->len) {
- /* Eat head of the next overlapped fragment
- * and leave the loop. The next ones cannot overlap.
- */
- if (!pskb_pull(next, i))
- goto err;
- FRAG6_CB(next)->offset += i; /* next fragment */
- fq->q.meat -= i;
- if (next->ip_summed != CHECKSUM_UNNECESSARY)
- next->ip_summed = CHECKSUM_NONE;
- break;
- } else {
- struct sk_buff *free_it = next;
-
- /* Old fragment is completely overridden with
- * new one drop it.
- */
- next = next->next;
-
- if (prev)
- prev->next = next;
- else
- fq->q.fragments = next;
-
- fq->q.meat -= free_it->len;
- frag_kfree_skb(fq->q.net, free_it, NULL);
- }
- }
+ /* Look for overlap with succeeding segment. */
+ if (next && FRAG6_CB(next)->offset < end)
+ goto discard_fq;

FRAG6_CB(skb)->offset = offset;

@@ -436,6 +390,8 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
write_unlock(&ip6_frags.lock);
return -1;

+discard_fq:
+ fq_kill(fq);
err:
IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
IPSTATS_MIB_REASMFAILS);
--
1.7.12.2.21.g234cd45.dirty




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