From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Jordy Zomer <jordy@pwning.systems>,
        "David S . Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>, steffen.klassert@secunet.com,
        yoshfuji@linux-ipv6.org, dsahern@kernel.org, kuba@kernel.org,
        netdev@vger.kernel.org
Subject: [PATCH AUTOSEL 5.15 30/39] ipv6: check return value of ipv6_skip_exthdr
Date:   Thu, 25 Nov 2021 21:31:47 -0500
Message-Id: <20211126023156.441292-30-sashal@kernel.org>
In-Reply-To: <20211126023156.441292-1-sashal@kernel.org>
References: <20211126023156.441292-1-sashal@kernel.org>
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From: Jordy Zomer <jordy@pwning.systems>

[ Upstream commit 5f9c55c8066bcd93ac25234a02585701fe2e31df ]

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv6/esp6.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index ed2f061b87685..f0bac6f7ab6bb 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;
-- 
2.33.0