netdev - [PATCH net-next 08/10] netfilter: nft_compat: add more restrictions on netlink attributes

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Message-ID: <20260120191803.22208-9-fw@strlen.de>
Date: Tue, 20 Jan 2026 20:18:01 +0100
From: Florian Westphal <fw@...len.de>
To: <netdev@...r.kernel.org>
Cc: Paolo Abeni <pabeni@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	<netfilter-devel@...r.kernel.org>,
	pablo@...filter.org
Subject: [PATCH net-next 08/10] netfilter: nft_compat: add more restrictions on netlink attributes

As far as I can see nothing bad can happen when NFTA_TARGET/MATCH_NAME
are too large because this calls x_tables helpers which check for the
length, but it seems better to already reject it during netlink parsing.

Rest of the changes avoid silent u8/u16 truncations.

For _TYPE, its expected to be only 1 or 0. In x_tables world, this
variable is set by kernel, for IPT_SO_GET_REVISION_TARGET its 1, for
all others its set to 0.

As older versions of nf_tables permitted any value except 1 to mean 'match',
keep this as-is but sanitize the value for consistency.

Fixes: 0ca743a55991 ("netfilter: nf_tables: add compatibility layer for x_tables")
Reviewed-by: Fernando Fernandez Mancera <fmancera@...e.de>
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/netfilter/nft_compat.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index 72711d62fddf..08f620311b03 100644
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -134,7 +134,8 @@ static void nft_target_eval_bridge(const struct nft_expr *expr,
 }
 
 static const struct nla_policy nft_target_policy[NFTA_TARGET_MAX + 1] = {
-	[NFTA_TARGET_NAME]	= { .type = NLA_NUL_STRING },
+	[NFTA_TARGET_NAME]	= { .type = NLA_NUL_STRING,
+				    .len = XT_EXTENSION_MAXNAMELEN, },
 	[NFTA_TARGET_REV]	= NLA_POLICY_MAX(NLA_BE32, 255),
 	[NFTA_TARGET_INFO]	= { .type = NLA_BINARY },
 };
@@ -434,7 +435,8 @@ static void nft_match_eval(const struct nft_expr *expr,
 }
 
 static const struct nla_policy nft_match_policy[NFTA_MATCH_MAX + 1] = {
-	[NFTA_MATCH_NAME]	= { .type = NLA_NUL_STRING },
+	[NFTA_MATCH_NAME]	= { .type = NLA_NUL_STRING,
+				    .len = XT_EXTENSION_MAXNAMELEN },
 	[NFTA_MATCH_REV]	= NLA_POLICY_MAX(NLA_BE32, 255),
 	[NFTA_MATCH_INFO]	= { .type = NLA_BINARY },
 };
@@ -693,7 +695,12 @@ static int nfnl_compat_get_rcu(struct sk_buff *skb,
 
 	name = nla_data(tb[NFTA_COMPAT_NAME]);
 	rev = ntohl(nla_get_be32(tb[NFTA_COMPAT_REV]));
-	target = ntohl(nla_get_be32(tb[NFTA_COMPAT_TYPE]));
+	/* x_tables api checks for 'target == 1' to mean target,
+	 * everything else means 'match'.
+	 * In x_tables world, the number is set by kernel, not
+	 * userspace.
+	 */
+	target = nla_get_be32(tb[NFTA_COMPAT_TYPE]) == htonl(1);
 
 	switch(family) {
 	case AF_INET:
-- 
2.52.0