linux-hardening - [PATCH] ipv6: check return value of ipv6_skip

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Message-Id: <20211117181610.2731938-1-jordy@pwning.systems>
Date:   Wed, 17 Nov 2021 19:16:10 +0100
From:   Jordy Zomer <jordy@...ing.systems>
To:     linux-kernel@...r.kernel.org
Cc:     linux-hardening@...r.kernel.org,
        Jordy Zomer <jordy@...ing.systems>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH] ipv6: check return value of ipv6_skip_exthdr

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.

Signed-off-by: Jordy Zomer <jordy@...ing.systems>
---
 net/ipv6/esp6.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index ed2f061b8768..dc4251655df9 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -808,6 +808,11 @@ 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