netdev - [PATCH nf] netfilter/xt_u32: validate user space input

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Message-ID: <20230828132107.18376-1-wander@redhat.com>
Date: Mon, 28 Aug 2023 10:21:07 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	Florian Westphal <fw@...len.de>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Patrick McHardy <kaber@...sh.net>,
	Jan Engelhardt <jengelh@....de>,
	netfilter-devel@...r.kernel.org (open list:NETFILTER),
	coreteam@...filter.org (open list:NETFILTER),
	netdev@...r.kernel.org (open list:NETWORKING [GENERAL]),
	linux-kernel@...r.kernel.org (open list)
Cc: Wander Lairson Costa <wander@...hat.com>
Subject: [PATCH nf] netfilter/xt_u32: validate user space input

The xt_u32 module doesn't validate the fields in the xt_u32 structure.
An attacker may take advantage of this to trigger an OOB read by setting
the size fields with a value beyond the arrays boundaries.

Add a checkentry function to validate the structure.

This was originally reported by the ZDI project (ZDI-CAN-18408).

Fixes: 1b50b8a371e9 ("[NETFILTER]: Add u32 match")
Signed-off-by: Wander Lairson Costa <wander@...hat.com>
---
 net/netfilter/xt_u32.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/net/netfilter/xt_u32.c b/net/netfilter/xt_u32.c
index 177b40d08098..117d4615d668 100644
--- a/net/netfilter/xt_u32.c
+++ b/net/netfilter/xt_u32.c
@@ -96,11 +96,32 @@ static bool u32_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	return ret ^ data->invert;
 }
 
+static int u32_mt_checkentry(const struct xt_mtchk_param *par)
+{
+	const struct xt_u32 *data = par->matchinfo;
+	const struct xt_u32_test *ct;
+	unsigned int i;
+
+	if (data->ntests > ARRAY_SIZE(data->tests))
+		return -EINVAL;
+
+	for (i = 0; i < data->ntests; ++i) {
+		ct = &data->tests[i];
+
+		if (ct->nnums > ARRAY_SIZE(ct->location) ||
+		    ct->nvalues > ARRAY_SIZE(ct->value))
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
 static struct xt_match xt_u32_mt_reg __read_mostly = {
 	.name       = "u32",
 	.revision   = 0,
 	.family     = NFPROTO_UNSPEC,
 	.match      = u32_mt,
+	.checkentry = u32_mt_checkentry,
 	.matchsize  = sizeof(struct xt_u32),
 	.me         = THIS_MODULE,
 };
-- 
2.41.0