netdev - [PATCH net 4/8] netfilter: nfnetlink_osf: Fix a missing skb_header

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Message-Id: <20210507174739.1850-5-pablo@netfilter.org>
Date:   Fri,  7 May 2021 19:47:35 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org
Subject: [PATCH net 4/8] 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: 11eeef41d5f6 ("netfilter: passive OS fingerprint xtables match")
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/netfilter/nfnetlink_osf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c
index e8f8875c6884..0fa2e2030427 100644
--- 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;
-- 
2.30.2