[PATCH net 04/14] netfilter: x_tables: add .check_hooks to matches and targets

Pablo Neira Ayuso
2026-05-01T12:22:49Z

Add a new .check_hooks interface for checking if the match/target is
used from the validate hook according to its configuration.

Move existing conditional hook check based on the match/target
configuration from .checkentry to .check_hooks for the following
matches/targets:

- addrtype
- devgroup
- physdev
- policy
- set
- TCPMSS
- SET

This is a preparation patch to fix nft_compat, not functional changes
are intended.

Based on patch from Florian Westphal.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
include/linux/netfilter/x_tables.h | 8 +++
net/netfilter/x_tables.c | 79 +++++++++++++++++++++++++++---
net/netfilter/xt_TCPMSS.c | 33 +++++++------
net/netfilter/xt_addrtype.c | 25 +++++++---
net/netfilter/xt_devgroup.c | 18 +++++--
net/netfilter/xt_physdev.c | 20 ++++++--
net/netfilter/xt_policy.c | 24 +++++++--
net/netfilter/xt_set.c | 39 +++++++++------
8 files changed, 187 insertions(+), 59 deletions(-)

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 77c778d84d4c..a81b46af5118 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -146,6 +146,9 @@ struct xt_match {
/* Called when user tries to insert an entry of this type. */
int (*checkentry)(const struct xt_mtchk_param *);

+ /* Called to validate hooks based on the match configuration. */
+ int (*check_hooks)(const struct xt_mtchk_param *);
+
/* Called when entry of this type deleted. */
void (*destroy)(const struct xt_mtdtor_param *);
#ifdef CONFIG_NETFILTER_XTABLES_COMPAT
@@ -187,6 +190,9 @@ struct xt_target {
/* Should return 0 on success or an error code otherwise (-Exxxx). */
int (*checkentry)(const struct xt_tgchk_param *);

+ /* Called to validate hooks based on the target configuration. */
+ int (*check_hooks)(const struct xt_tgchk_param *);
+
/* Called when entry of this type deleted. */
void (*destroy)(const struct xt_tgdtor_param *);
#ifdef CONFIG_NETFILTER_XTABLES_COMPAT
@@ -279,8 +285,10 @@ bool xt_find_jump_offset(const unsigned int *offsets,

int xt_check_proc_name(const char *name, unsigned int size);

+int xt_check_hooks_match(struct xt_mtchk_param *par);
int xt_check_match(struct xt_mtchk_param *, unsigned int size, u16 proto,
bool inv_proto);
+int xt_check_hooks_target(struct xt_tgchk_param *par);
int xt_check_target(struct xt_tgchk_param *, unsigned int size, u16 proto,
bool inv_proto);

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 9f837fb5ceb4..2c67c2e6b132 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -477,11 +477,9 @@ int xt_check_proc_name(const char *name, unsigned int size)
}
EXPORT_SYMBOL(xt_check_proc_name);

-int xt_check_match(struct xt_mtchk_param *par,
- unsigned int size, u16 proto, bool inv_proto)
+static int xt_check_match_common(struct xt_mtchk_param *par,
+ unsigned int size, u16 proto, bool inv_proto)
{
- int ret;
-
if (XT_ALIGN(par->match->matchsize) != size &&
par->match->matchsize != -1) {
/*
@@ -530,6 +528,14 @@ int xt_check_match(struct xt_mtchk_param *par,
par->match->proto);
return -EINVAL;
}
+
+ return 0;
+}
+
+static int xt_checkentry_match(struct xt_mtchk_param *par)
+{
+ int ret;
+
if (par->match->checkentry != NULL) {
ret = par->match->checkentry(par);
if (ret < 0)
@@ -538,8 +544,34 @@ int xt_check_match(struct xt_mtchk_param *par,
/* Flag up potential errors. */
return -EIO;
}
+
+ return 0;
+}
+
+int xt_check_hooks_match(struct xt_mtchk_param *par)
+{
+ if (par->match->check_hooks != NULL)
+ return par->match->check_hooks(par);
+
return 0;
}
+EXPORT_SYMBOL_GPL(xt_check_hooks_match);
+
+int xt_check_match(struct xt_mtchk_param *par,
+ unsigned int size, u16 proto, bool inv_proto)
+{
+ int ret;
+
+ ret = xt_check_match_common(par, size, proto, inv_proto);
+ if (ret < 0)
+ return ret;
+
+ ret = xt_check_hooks_match(par);
+ if (ret < 0)
+ return ret;
+
+ return xt_checkentry_match(par);
+}
EXPORT_SYMBOL_GPL(xt_check_match);

/** xt_check_entry_match - check that matches end before start of target
@@ -1012,11 +1044,9 @@ bool xt_find_jump_offset(const unsigned int *offsets,
}
EXPORT_SYMBOL(xt_find_jump_offset);

-int xt_check_target(struct xt_tgchk_param *par,
- unsigned int size, u16 proto, bool inv_proto)
+static int xt_check_target_common(struct xt_tgchk_param *par,
+ unsigned int size, u16 proto, bool inv_proto)
{
- int ret;
-
if (XT_ALIGN(par->target->targetsize) != size) {
pr_err_ratelimited("%s_tables: %s.%u target: invalid size %u (kernel) != (user) %u\n",
xt_prefix[par->family], par->target->name,
@@ -1061,6 +1091,23 @@ int xt_check_target(struct xt_tgchk_param *par,
par->target->proto);
return -EINVAL;
}
+
+ return 0;
+}
+
+int xt_check_hooks_target(struct xt_tgchk_param *par)
+{
+ if (par->target->check_hooks != NULL)
+ return par->target->check_hooks(par);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(xt_check_hooks_target);
+
+static int xt_checkentry_target(struct xt_tgchk_param *par)
+{
+ int ret;
+
if (par->target->checkentry != NULL) {
ret = par->target->checkentry(par);
if (ret < 0)
@@ -1071,6 +1118,22 @@ int xt_check_target(struct xt_tgchk_param *par,
}
return 0;
}
+
+int xt_check_target(struct xt_tgchk_param *par,
+ unsigned int size, u16 proto, bool inv_proto)
+{
+ int ret;
+
+ ret = xt_check_target_common(par, size, proto, inv_proto);
+ if (ret < 0)
+ return ret;
+
+ ret = xt_check_hooks_target(par);
+ if (ret < 0)
+ return ret;
+
+ return xt_checkentry_target(par);
+}
EXPORT_SYMBOL_GPL(xt_check_target);

/**
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 116a885adb3c..80e1634bc51f 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -247,6 +247,21 @@ tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
}
#endif

+static int tcpmss_tg4_check_hooks(const struct xt_tgchk_param *par)
+{
+ const struct xt_tcpmss_info *info = par->targinfo;
+
+ if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
+ (par->hook_mask & ~((1 << NF_INET_FORWARD) |
+ (1 << NF_INET_LOCAL_OUT) |
+ (1 << NF_INET_POST_ROUTING))) != 0) {
+ pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
/* Must specify -p tcp --syn */
static inline bool find_syn_match(const struct xt_entry_match *m)
{
@@ -262,17 +277,9 @@ static inline bool find_syn_match(const struct xt_entry_match *m)

static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
{
- const struct xt_tcpmss_info *info = par->targinfo;
const struct ipt_entry *e = par->entryinfo;
const struct xt_entry_match *ematch;

- if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
- (par->hook_mask & ~((1 << NF_INET_FORWARD) |
- (1 << NF_INET_LOCAL_OUT) |
- (1 << NF_INET_POST_ROUTING))) != 0) {
- pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
- return -EINVAL;
- }
if (par->nft_compat)
return 0;

@@ -286,17 +293,9 @@ static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
{
- const struct xt_tcpmss_info *info = par->targinfo;
const struct ip6t_entry *e = par->entryinfo;
const struct xt_entry_match *ematch;

- if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
- (par->hook_mask & ~((1 << NF_INET_FORWARD) |
- (1 << NF_INET_LOCAL_OUT) |
- (1 << NF_INET_POST_ROUTING))) != 0) {
- pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
- return -EINVAL;
- }
if (par->nft_compat)
return 0;

@@ -312,6 +311,7 @@ static struct xt_target tcpmss_tg_reg[] __read_mostly = {
{
.family = NFPROTO_IPV4,
.name = "TCPMSS",
+ .check_hooks = tcpmss_tg4_check_hooks,
.checkentry = tcpmss_tg4_check,
.target = tcpmss_tg4,
.targetsize = sizeof(struct xt_tcpmss_info),
@@ -322,6 +322,7 @@ static struct xt_target tcpmss_tg_reg[] __read_mostly = {
{
.family = NFPROTO_IPV6,
.name = "TCPMSS",
+ .check_hooks = tcpmss_tg4_check_hooks,
.checkentry = tcpmss_tg6_check,
.target = tcpmss_tg6,
.targetsize = sizeof(struct xt_tcpmss_info),
diff --git a/net/netfilter/xt_addrtype.c b/net/netfilter/xt_addrtype.c
index a77088943107..913dbe3aa5e2 100644
--- a/net/netfilter/xt_addrtype.c
+++ b/net/netfilter/xt_addrtype.c
@@ -153,14 +153,10 @@ addrtype_mt_v1(const struct sk_buff *skb, struct xt_action_param *par)
return ret;
}

-static int addrtype_mt_checkentry_v1(const struct xt_mtchk_param *par)
+static int addrtype_mt_check_hooks(const struct xt_mtchk_param *par)
{
- const char *errmsg = "both incoming and outgoing interface limitation cannot be selected";
struct xt_addrtype_info_v1 *info = par->matchinfo;
-
- if (info->flags & XT_ADDRTYPE_LIMIT_IFACE_IN &&
- info->flags & XT_ADDRTYPE_LIMIT_IFACE_OUT)
- goto err;
+ const char *errmsg;

if (par->hook_mask & ((1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN)) &&
@@ -176,6 +172,21 @@ static int addrtype_mt_checkentry_v1(const struct xt_mtchk_param *par)
goto err;
}

+ return 0;
+err:
+ pr_info_ratelimited("%s\n", errmsg);
+ return -EINVAL;
+}
+
+static int addrtype_mt_checkentry_v1(const struct xt_mtchk_param *par)
+{
+ const char *errmsg = "both incoming and outgoing interface limitation cannot be selected";
+ struct xt_addrtype_info_v1 *info = par->matchinfo;
+
+ if (info->flags & XT_ADDRTYPE_LIMIT_IFACE_IN &&
+ info->flags & XT_ADDRTYPE_LIMIT_IFACE_OUT)
+ goto err;
+
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
if (par->family == NFPROTO_IPV6) {
if ((info->source | info->dest) & XT_ADDRTYPE_BLACKHOLE) {
@@ -211,6 +222,7 @@ static struct xt_match addrtype_mt_reg[] __read_mostly = {
.family = NFPROTO_IPV4,
.revision = 1,
.match = addrtype_mt_v1,
+ .check_hooks = addrtype_mt_check_hooks,
.checkentry = addrtype_mt_checkentry_v1,
.matchsize = sizeof(struct xt_addrtype_info_v1),
.me = THIS_MODULE
@@ -221,6 +233,7 @@ static struct xt_match addrtype_mt_reg[] __read_mostly = {
.family = NFPROTO_IPV6,
.revision = 1,
.match = addrtype_mt_v1,
+ .check_hooks = addrtype_mt_check_hooks,
.checkentry = addrtype_mt_checkentry_v1,
.matchsize = sizeof(struct xt_addrtype_info_v1),
.me = THIS_MODULE
diff --git a/net/netfilter/xt_devgroup.c b/net/netfilter/xt_devgroup.c
index 9520dd00070b..6d1a44ab5eee 100644
--- a/net/netfilter/xt_devgroup.c
+++ b/net/netfilter/xt_devgroup.c
@@ -33,14 +33,10 @@ static bool devgroup_mt(const struct sk_buff *skb, struct xt_action_param *par)
return true;
}

-static int devgroup_mt_checkentry(const struct xt_mtchk_param *par)
+static int devgroup_mt_check_hooks(const struct xt_mtchk_param *par)
{
const struct xt_devgroup_info *info = par->matchinfo;

- if (info->flags & ~(XT_DEVGROUP_MATCH_SRC | XT_DEVGROUP_INVERT_SRC |
- XT_DEVGROUP_MATCH_DST | XT_DEVGROUP_INVERT_DST))
- return -EINVAL;
-
if (info->flags & XT_DEVGROUP_MATCH_SRC &&
par->hook_mask & ~((1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN) |
@@ -56,9 +52,21 @@ static int devgroup_mt_checkentry(const struct xt_mtchk_param *par)
return 0;
}

+static int devgroup_mt_checkentry(const struct xt_mtchk_param *par)
+{
+ const struct xt_devgroup_info *info = par->matchinfo;
+
+ if (info->flags & ~(XT_DEVGROUP_MATCH_SRC | XT_DEVGROUP_INVERT_SRC |
+ XT_DEVGROUP_MATCH_DST | XT_DEVGROUP_INVERT_DST))
+ return -EINVAL;
+
+ return 0;
+}
+
static struct xt_match devgroup_mt_reg __read_mostly = {
.name = "devgroup",
.match = devgroup_mt,
+ .check_hooks = devgroup_mt_check_hooks,
.checkentry = devgroup_mt_checkentry,
.matchsize = sizeof(struct xt_devgroup_info),
.family = NFPROTO_UNSPEC,
diff --git a/net/netfilter/xt_physdev.c b/net/netfilter/xt_physdev.c
index d2b0b52434fa..dd98f758176c 100644
--- a/net/netfilter/xt_physdev.c
+++ b/net/netfilter/xt_physdev.c
@@ -91,14 +91,10 @@ physdev_mt(const struct sk_buff *skb, struct xt_action_param *par)
return (!!ret ^ !(info->invert & XT_PHYSDEV_OP_OUT));
}

-static int physdev_mt_check(const struct xt_mtchk_param *par)
+static int physdev_mt_check_hooks(const struct xt_mtchk_param *par)
{
const struct xt_physdev_info *info = par->matchinfo;
- static bool brnf_probed __read_mostly;

- if (!(info->bitmask & XT_PHYSDEV_OP_MASK) ||
- info->bitmask & ~XT_PHYSDEV_OP_MASK)
- return -EINVAL;
if (info->bitmask & (XT_PHYSDEV_OP_OUT | XT_PHYSDEV_OP_ISOUT) &&
(!(info->bitmask & XT_PHYSDEV_OP_BRIDGED) ||
info->invert & XT_PHYSDEV_OP_BRIDGED) &&
@@ -107,6 +103,18 @@ static int physdev_mt_check(const struct xt_mtchk_param *par)
return -EINVAL;
}

+ return 0;
+}
+
+static int physdev_mt_check(const struct xt_mtchk_param *par)
+{
+ const struct xt_physdev_info *info = par->matchinfo;
+ static bool brnf_probed __read_mostly;
+
+ if (!(info->bitmask & XT_PHYSDEV_OP_MASK) ||
+ info->bitmask & ~XT_PHYSDEV_OP_MASK)
+ return -EINVAL;
+
#define X(memb) strnlen(info->memb, sizeof(info->memb)) >= sizeof(info->memb)
if (info->bitmask & XT_PHYSDEV_OP_IN) {
if (info->physindev[0] == '\0')
@@ -141,6 +149,7 @@ static struct xt_match physdev_mt_reg[] __read_mostly = {
{
.name = "physdev",
.family = NFPROTO_IPV4,
+ .check_hooks = physdev_mt_check_hooks,
.checkentry = physdev_mt_check,
.match = physdev_mt,
.matchsize = sizeof(struct xt_physdev_info),
@@ -149,6 +158,7 @@ static struct xt_match physdev_mt_reg[] __read_mostly = {
{
.name = "physdev",
.family = NFPROTO_IPV6,
+ .check_hooks = physdev_mt_check_hooks,
.checkentry = physdev_mt_check,
.match = physdev_mt,
.matchsize = sizeof(struct xt_physdev_info),
diff --git a/net/netfilter/xt_policy.c b/net/netfilter/xt_policy.c
index b5fa65558318..ff54e3a8581e 100644
--- a/net/netfilter/xt_policy.c
+++ b/net/netfilter/xt_policy.c
@@ -126,13 +126,10 @@ policy_mt(const struct sk_buff *skb, struct xt_action_param *par)
return ret;
}

-static int policy_mt_check(const struct xt_mtchk_param *par)
+static int policy_mt_check_hooks(const struct xt_mtchk_param *par)
{
const struct xt_policy_info *info = par->matchinfo;
- const char *errmsg = "neither incoming nor outgoing policy selected";
-
- if (!(info->flags & (XT_POLICY_MATCH_IN|XT_POLICY_MATCH_OUT)))
- goto err;
+ const char *errmsg;

if (par->hook_mask & ((1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN)) && info->flags & XT_POLICY_MATCH_OUT) {
@@ -144,6 +141,21 @@ static int policy_mt_check(const struct xt_mtchk_param *par)
errmsg = "input policy not valid in POSTROUTING and OUTPUT";
goto err;
}
+
+ return 0;
+err:
+ pr_info_ratelimited("%s\n", errmsg);
+ return -EINVAL;
+}
+
+static int policy_mt_check(const struct xt_mtchk_param *par)
+{
+ const struct xt_policy_info *info = par->matchinfo;
+ const char *errmsg = "neither incoming nor outgoing policy selected";
+
+ if (!(info->flags & (XT_POLICY_MATCH_IN|XT_POLICY_MATCH_OUT)))
+ goto err;
+
if (info->len > XT_POLICY_MAX_ELEM) {
errmsg = "too many policy elements";
goto err;
@@ -158,6 +170,7 @@ static struct xt_match policy_mt_reg[] __read_mostly = {
{
.name = "policy",
.family = NFPROTO_IPV4,
+ .check_hooks = policy_mt_check_hooks,
.checkentry = policy_mt_check,
.match = policy_mt,
.matchsize = sizeof(struct xt_policy_info),
@@ -166,6 +179,7 @@ static struct xt_match policy_mt_reg[] __read_mostly = {
{
.name = "policy",
.family = NFPROTO_IPV6,
+ .check_hooks = policy_mt_check_hooks,
.checkentry = policy_mt_check,
.match = policy_mt,
.matchsize = sizeof(struct xt_policy_info),
diff --git a/net/netfilter/xt_set.c b/net/netfilter/xt_set.c
index 731bc2cafae4..4ae04bba9358 100644
--- a/net/netfilter/xt_set.c
+++ b/net/netfilter/xt_set.c
@@ -430,6 +430,29 @@ set_target_v3(struct sk_buff *skb, const struct xt_action_param *par)
return XT_CONTINUE;
}

+static int
+set_target_v3_check_hooks(const struct xt_tgchk_param *par)
+{
+ const struct xt_set_info_target_v3 *info = par->targinfo;
+
+ if (info->map_set.index != IPSET_INVALID_ID) {
+ if (strncmp(par->table, "mangle", 7)) {
+ pr_info_ratelimited("--map-set only usable from mangle table\n");
+ return -EINVAL;
+ }
+ if (((info->flags & IPSET_FLAG_MAP_SKBPRIO) |
+ (info->flags & IPSET_FLAG_MAP_SKBQUEUE)) &&
+ (par->hook_mask & ~(1 << NF_INET_FORWARD |
+ 1 << NF_INET_LOCAL_OUT |
+ 1 << NF_INET_POST_ROUTING))) {
+ pr_info_ratelimited("mapping of prio or/and queue is allowed only from OUTPUT/FORWARD/POSTROUTING chains\n");
+ return -EINVAL;
+ }
+ }
+
+ return 0;
+}
+
static int
set_target_v3_checkentry(const struct xt_tgchk_param *par)
{
@@ -459,20 +482,6 @@ set_target_v3_checkentry(const struct xt_tgchk_param *par)
}

if (info->map_set.index != IPSET_INVALID_ID) {
- if (strncmp(par->table, "mangle", 7)) {
- pr_info_ratelimited("--map-set only usable from mangle table\n");
- ret = -EINVAL;
- goto cleanup_del;
- }
- if (((info->flags & IPSET_FLAG_MAP_SKBPRIO) |
- (info->flags & IPSET_FLAG_MAP_SKBQUEUE)) &&
- (par->hook_mask & ~(1 << NF_INET_FORWARD |
- 1 << NF_INET_LOCAL_OUT |
- 1 << NF_INET_POST_ROUTING))) {
- pr_info_ratelimited("mapping of prio or/and queue is allowed only from OUTPUT/FORWARD/POSTROUTING chains\n");
- ret = -EINVAL;
- goto cleanup_del;
- }
index = ip_set_nfnl_get_byindex(par->net,
info->map_set.index);
if (index == IPSET_INVALID_ID) {
@@ -672,6 +681,7 @@ static struct xt_target set_targets[] __read_mostly = {
.family = NFPROTO_IPV4,
.target = set_target_v3,
.targetsize = sizeof(struct xt_set_info_target_v3),
+ .check_hooks = set_target_v3_check_hooks,
.checkentry = set_target_v3_checkentry,
.destroy = set_target_v3_destroy,
.me = THIS_MODULE
@@ -682,6 +692,7 @@ static struct xt_target set_targets[] __read_mostly = {
.family = NFPROTO_IPV6,
.target = set_target_v3,
.targetsize = sizeof(struct xt_set_info_target_v3),
+ .check_hooks = set_target_v3_check_hooks,
.checkentry = set_target_v3_checkentry,
.destroy = set_target_v3_destroy,
.me = THIS_MODULE
--
2.47.3