[PATCH 06/19] netfilter: nf_conntrack_ipv6: fix tracking of ICMPv6 error messages containing fragments

kaber
2012-08-09T20:18:35Z

From: Patrick McHardy <kaber@trash.net>

ICMPv6 error messages are tracked by extracting the conntrack tuple of
the inner packet and looking up the corresponding conntrack entry. Tuple
extraction uses the ->get_l4proto() callback, which in case of fragments
returns NEXTHDR_FRAGMENT instead of the upper protocol, even for the
first fragment when the entire next header is present, resulting in a
failure to find the correct connection tracking entry.

This patch changes ipv6_get_l4proto() to use ipv6_skip_exthdr() instead
of nf_ct_ipv6_skip_exthdr() in order to skip fragment headers when the
fragment offset is zero.

Signed-off-by: Patrick McHardy <kaber@trash.net>
---
net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c | 63 ++---------------------
1 files changed, 6 insertions(+), 57 deletions(-)

diff --git a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
index 560d823..4d92ea6 100644
--- a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
+++ b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
@@ -64,82 +64,31 @@ static int ipv6_print_tuple(struct seq_file *s,
tuple->src.u3.ip6, tuple->dst.u3.ip6);
}

-/*
- * Based on ipv6_skip_exthdr() in net/ipv6/exthdr.c
- *
- * This function parses (probably truncated) exthdr set "hdr"
- * of length "len". "nexthdrp" initially points to some place,
- * where type of the first header can be found.
- *
- * It skips all well-known exthdrs, and returns pointer to the start
- * of unparsable area i.e. the first header with unknown type.
- * if success, *nexthdr is updated by type/protocol of this header.
- *
- * NOTES: - it may return pointer pointing beyond end of packet,
- * if the last recognized header is truncated in the middle.
- * - if packet is truncated, so that all parsed headers are skipped,
- * it returns -1.
- * - if packet is fragmented, return pointer of the fragment header.
- * - ESP is unparsable for now and considered like
- * normal payload protocol.
- * - Note also special handling of AUTH header. Thanks to IPsec wizards.
- */
-
-static int nf_ct_ipv6_skip_exthdr(const struct sk_buff *skb, int start,
- u8 *nexthdrp, int len)
-{
- u8 nexthdr = *nexthdrp;
-
- while (ipv6_ext_hdr(nexthdr)) {
- struct ipv6_opt_hdr hdr;
- int hdrlen;
-
- if (len < (int)sizeof(struct ipv6_opt_hdr))
- return -1;
- if (nexthdr == NEXTHDR_NONE)
- break;
- if (nexthdr == NEXTHDR_FRAGMENT)
- break;
- if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
- BUG();
- if (nexthdr == NEXTHDR_AUTH)
- hdrlen = (hdr.hdrlen+2)<<2;
- else
- hdrlen = ipv6_optlen(&hdr);
-
- nexthdr = hdr.nexthdr;
- len -= hdrlen;
- start += hdrlen;
- }
-
- *nexthdrp = nexthdr;
- return start;
-}
-
static int ipv6_get_l4proto(const struct sk_buff *skb, unsigned int nhoff,
unsigned int *dataoff, u_int8_t *protonum)
{
unsigned int extoff = nhoff + sizeof(struct ipv6hdr);
- unsigned char pnum;
+ __be16 frag_off;
int protoff;
+ u8 nexthdr;

if (skb_copy_bits(skb, nhoff + offsetof(struct ipv6hdr, nexthdr),
- &pnum, sizeof(pnum)) != 0) {
+ &nexthdr, sizeof(nexthdr)) != 0) {
pr_debug("ip6_conntrack_core: can't get nexthdr\n");
return -NF_ACCEPT;
}
- protoff = nf_ct_ipv6_skip_exthdr(skb, extoff, &pnum, skb->len - extoff);
+ protoff = ipv6_skip_exthdr(skb, extoff, &nexthdr, &frag_off);
/*
* (protoff == skb->len) mean that the packet doesn't have no data
* except of IPv6 & ext headers. but it's tracked anyway. - YK
*/
- if ((protoff < 0) || (protoff > skb->len)) {
+ if (protoff < 0 || (frag_off & ntohs(~0x7)) != 0) {
pr_debug("ip6_conntrack_core: can't find proto in pkt\n");
return -NF_ACCEPT;
}

*dataoff = protoff;
- *protonum = pnum;
+ *protonum = nexthdr;
return NF_ACCEPT;
}

--
1.7.1