Add pr_fmt to prefix log messages with the module name for
easier debugging in dmesg.

Add checkentry functions for IPv4 (ttl_mt_check) and IPv6
(hl_mt6_check) to validate the match mode at rule registration
time, rejecting invalid modes with -EINVAL.

Signed-off-by: Marino Dzalto <marino.dzalto@gmail.com>
---
v3: Remove mention of NULL checks from commit message, as they
    were never part of the original code.
v2: Remove NULL checks for skb as suggested by Florian Westphal
    (skb is guaranteed non-NULL by netfilter core). Move mode
    validation to checkentry functions instead of match function,
    also as suggested by Florian Westphal.
---
 net/netfilter/xt_hl.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/net/netfilter/xt_hl.c b/net/netfilter/xt_hl.c
index c1a70f8f0441..4a12a757ecbf 100644
--- a/net/netfilter/xt_hl.c
+++ b/net/netfilter/xt_hl.c
@@ -6,6 +6,7 @@
  * Hop Limit matching module
  * (C) 2001-2002 Maciej Soltysiak <solt@dns.toxicfilms.tv>
  */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/ip.h>
 #include <linux/ipv6.h>
@@ -22,6 +23,18 @@ MODULE_LICENSE("GPL");
 MODULE_ALIAS("ipt_ttl");
 MODULE_ALIAS("ip6t_hl");
 
+static int ttl_mt_check(const struct xt_mtchk_param *par)
+{
+	const struct ipt_ttl_info *info = par->matchinfo;
+
+	if (info->mode > IPT_TTL_GT) {
+		pr_err("Unknown TTL match mode: %d\n", info->mode);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static bool ttl_mt(const struct sk_buff *skb, struct xt_action_param *par)
 {
 	const struct ipt_ttl_info *info = par->matchinfo;
@@ -41,6 +54,18 @@ static bool ttl_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	return false;
 }
 
+static int hl_mt6_check(const struct xt_mtchk_param *par)
+{
+	const struct ip6t_hl_info *info = par->matchinfo;
+
+	if (info->mode > IP6T_HL_GT) {
+		pr_err("Unknown Hop Limit match mode: %d\n", info->mode);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static bool hl_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 {
 	const struct ip6t_hl_info *info = par->matchinfo;
@@ -65,6 +90,7 @@ static struct xt_match hl_mt_reg[] __read_mostly = {
 		.name       = "ttl",
 		.revision   = 0,
 		.family     = NFPROTO_IPV4,
+		.checkentry = ttl_mt_check,
 		.match      = ttl_mt,
 		.matchsize  = sizeof(struct ipt_ttl_info),
 		.me         = THIS_MODULE,
@@ -73,6 +99,7 @@ static struct xt_match hl_mt_reg[] __read_mostly = {
 		.name       = "hl",
 		.revision   = 0,
 		.family     = NFPROTO_IPV6,
+		.checkentry = hl_mt6_check,
 		.match      = hl_mt6,
 		.matchsize  = sizeof(struct ip6t_hl_info),
 		.me         = THIS_MODULE,
-- 
2.50.1 (Apple Git-155)

On Fri, Apr 03, 2026 at 10:59:07PM +0200, Marino Dzalto wrote:
> Add pr_fmt to prefix log messages with the module name for
> easier debugging in dmesg.
> 
> Add checkentry functions for IPv4 (ttl_mt_check) and IPv6
> (hl_mt6_check) to validate the match mode at rule registration
> time, rejecting invalid modes with -EINVAL.
> 
> Signed-off-by: Marino Dzalto <marino.dzalto@gmail.com>
> ---

BTW, please use "nf-next" as target tree for this.

And use _ratelimited as suggested by the AI reviewer.

Send us a v4, thanks

> v3: Remove mention of NULL checks from commit message, as they
>     were never part of the original code.
> v2: Remove NULL checks for skb as suggested by Florian Westphal
>     (skb is guaranteed non-NULL by netfilter core). Move mode
>     validation to checkentry functions instead of match function,
>     also as suggested by Florian Westphal.
> ---
>  net/netfilter/xt_hl.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/net/netfilter/xt_hl.c b/net/netfilter/xt_hl.c
> index c1a70f8f0441..4a12a757ecbf 100644
> --- a/net/netfilter/xt_hl.c
> +++ b/net/netfilter/xt_hl.c
> @@ -6,6 +6,7 @@
>   * Hop Limit matching module
>   * (C) 2001-2002 Maciej Soltysiak <solt@dns.toxicfilms.tv>
>   */
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
>  #include <linux/ip.h>
>  #include <linux/ipv6.h>
> @@ -22,6 +23,18 @@ MODULE_LICENSE("GPL");
>  MODULE_ALIAS("ipt_ttl");
>  MODULE_ALIAS("ip6t_hl");
>  
> +static int ttl_mt_check(const struct xt_mtchk_param *par)
> +{
> +	const struct ipt_ttl_info *info = par->matchinfo;
> +
> +	if (info->mode > IPT_TTL_GT) {
> +		pr_err("Unknown TTL match mode: %d\n", info->mode);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static bool ttl_mt(const struct sk_buff *skb, struct xt_action_param *par)
>  {
>  	const struct ipt_ttl_info *info = par->matchinfo;
> @@ -41,6 +54,18 @@ static bool ttl_mt(const struct sk_buff *skb, struct xt_action_param *par)
>  	return false;
>  }
>  
> +static int hl_mt6_check(const struct xt_mtchk_param *par)
> +{
> +	const struct ip6t_hl_info *info = par->matchinfo;
> +
> +	if (info->mode > IP6T_HL_GT) {
> +		pr_err("Unknown Hop Limit match mode: %d\n", info->mode);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static bool hl_mt6(const struct sk_buff *skb, struct xt_action_param *par)
>  {
>  	const struct ip6t_hl_info *info = par->matchinfo;
> @@ -65,6 +90,7 @@ static struct xt_match hl_mt_reg[] __read_mostly = {
>  		.name       = "ttl",
>  		.revision   = 0,
>  		.family     = NFPROTO_IPV4,
> +		.checkentry = ttl_mt_check,
>  		.match      = ttl_mt,
>  		.matchsize  = sizeof(struct ipt_ttl_info),
>  		.me         = THIS_MODULE,
> @@ -73,6 +99,7 @@ static struct xt_match hl_mt_reg[] __read_mostly = {
>  		.name       = "hl",
>  		.revision   = 0,
>  		.family     = NFPROTO_IPV6,
> +		.checkentry = hl_mt6_check,
>  		.match      = hl_mt6,
>  		.matchsize  = sizeof(struct ip6t_hl_info),
>  		.me         = THIS_MODULE,
> -- 
> 2.50.1 (Apple Git-155)
>