From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Wed, 5 May 2021 20:25:24 +0000 (+0200)
Subject: netfilter: nfnetlink_osf: Fix a missing skb_header_pointer() NULL check
X-Git-Tag: v4.19.191~68
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e11924b7513ceacd7e9a0ed9f8db60629eefbf12;p=thirdparty%2Fkernel%2Fstable.git

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

[ Upstream commit 5e024c325406470d1165a09c6feaf8ec897936be ]

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@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c
index 131f9f8c0b092..917f06110c823 100644
--- a/net/netfilter/nfnetlink_osf.c
+++ b/net/netfilter/nfnetlink_osf.c
@@ -191,6 +191,8 @@ 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;