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netfilter: conntrack: fix false CRC32c mismatch using paged skb

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sctp_compute_cksum() implementation assumes that at least the SCTP header
is in the linear part of skb: modify conntrack error callback to avoid
false CRC32c mismatch, if the transport header is partially/entirely paged.

Fixes: cf6e007eef ("netfilter: conntrack: validate SCTP crc32c in PREROUTING")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Davide Caratti 2017-05-18 18:01:43 +02:00 committed by Pablo Neira Ayuso
parent 6d18c732b9
commit f3c0eb05e2
1 changed files with 6 additions and 3 deletions
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9
net/netfilter/nf_conntrack_proto_sctp.c
View file

@ -512,16 +512,19 @@ static int sctp_error(struct net *net, struct nf_conn *tpl, struct sk_buff *skb,
u8 pf, unsigned int hooknum)
{
const struct sctphdr *sh;
struct sctphdr _sctph;
const char *logmsg;
sh = skb_header_pointer(skb, dataoff, sizeof(_sctph), &_sctph);
if (!sh) {
if (skb->len < dataoff + sizeof(struct sctphdr)) {
logmsg = "nf_ct_sctp: short packet ";
goto out_invalid;
}
if (net->ct.sysctl_checksum && hooknum == NF_INET_PRE_ROUTING &&
skb->ip_summed == CHECKSUM_NONE) {
if (!skb_make_writable(skb, dataoff + sizeof(struct sctphdr))) {
logmsg = "nf_ct_sctp: failed to read header ";
goto out_invalid;
}
sh = (const struct sctphdr *)(skb->data + dataoff);
if (sh->checksum != sctp_compute_cksum(skb, dataoff)) {
logmsg = "nf_ct_sctp: bad CRC ";
goto out_invalid;