From:   Jordy Zomer <jordy@pwning.systems>
To:     linux-kernel@vger.kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        Jordy Zomer <jordy@pwning.systems>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org
Subject: [PATCH v2] ipv6: check return value of ipv6_skip_exthdr
Date:   Wed, 17 Nov 2021 20:06:48 +0100
Message-Id: <20211117190648.2732560-1-jordy@pwning.systems>
In-Reply-To: <20211117181610.2731938-1-jordy@pwning.systems>
References: <20211117181610.2731938-1-jordy@pwning.systems>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The offset value is used in pointer math on skb->data.
Since ipv6_skip_exthdr may return -1 the pointer to uh and th
may not point to the actual udp and tcp headers and potentially
overwrite other stuff. This is why I think this should be checked.

EDIT:  added {}'s, thanks Kees

Signed-off-by: Jordy Zomer <jordy@pwning.systems>
---
 net/ipv6/esp6.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index ed2f061b8768..f0bac6f7ab6b 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -808,6 +808,12 @@ int esp6_input_done2(struct sk_buff *skb, int err)
 		struct tcphdr *th;
 
 		offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off);
+
+		if (offset < 0) {
+			err = -EINVAL;
+			goto out;
+		}
+
 		uh = (void *)(skb->data + offset);
 		th = (void *)(skb->data + offset);
 		hdr_len += offset;
-- 
2.27.0