netfilter: nfnetlink_osf: Fix a missing skb_header_pointer() NULL check

Do not assume that the tcph->doff field is correct when parsing for TCP
options, skb_header_pointer() might fail to fetch these bits.

Fixes: 82f337bd3ffb ("netfilter: passive OS fingerprint xtables match")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c
index e8f8875c6884e16771053a8ae2d8984dd0249d10..0fa2e203042728582b9860a6bdd1f798210637af 100644 (file)
--- a/net/netfilter/nfnetlink_osf.c
+++ b/net/netfilter/nfnetlink_osf.c
@@ -186,6 +186,8 @@ static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
 
                ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
                                sizeof(struct tcphdr), ctx->optsize, opts);
+               if (!ctx->optp)
+                       return NULL;
        }
 
        return tcp;