[PATCH] netfilter: Make xt_cgroup independent from net_cls

[Michal Koutný <mkoutny@xxxxxxxx>]

The xt_group matching supports the default hierarchy since commit
c38c4597e4bf3 ("netfilter: implement xt_cgroup cgroup2 path match").
The cgroup v1 matching (based on clsid) and cgroup v2 matching (based on
path) are rather independent. Adjust Kconfig so that xt_group can be
built even without CONFIG_NET_CLS_CGROUP for path matching. Also add a
message for users when they attempt to specify any non-trivial clsid.

Link: https://lists.opensuse.org/archives/list/kernel@xxxxxxxxxxxxxxxxxx/thread/S23NOILB7MUIRHSKPBOQKJHVSK26GP6X/
Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
---
 net/netfilter/Kconfig     |  1 -
 net/netfilter/xt_cgroup.c | 23 +++++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index df2dc21304efb..af9350386033e 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -1180,7 +1180,6 @@ config NETFILTER_XT_MATCH_CGROUP
 	tristate '"control group" match support'
 	depends on NETFILTER_ADVANCED
 	depends on CGROUPS
-	select CGROUP_NET_CLASSID
 	help
 	Socket/process control group matching allows you to match locally
 	generated packets based on which net_cls control group processes
diff --git a/net/netfilter/xt_cgroup.c b/net/netfilter/xt_cgroup.c
index c0f5e9a4f3c65..f30a62e803d22 100644
--- a/net/netfilter/xt_cgroup.c
+++ b/net/netfilter/xt_cgroup.c
@@ -23,6 +23,14 @@ MODULE_DESCRIPTION("Xtables: process control group matching");
 MODULE_ALIAS("ipt_cgroup");
 MODULE_ALIAS("ip6t_cgroup");
 
+static bool possible_classid(u32 classid)
+{
+	if (!IS_ENABLED(CONFIG_CGROUP_NET_CLASSID) && classid > 0)
+		return false;
+	else
+		return true;
+}
+
 static int cgroup_mt_check_v0(const struct xt_mtchk_param *par)
 {
 	struct xt_cgroup_info_v0 *info = par->matchinfo;
@@ -30,6 +38,11 @@ static int cgroup_mt_check_v0(const struct xt_mtchk_param *par)
 	if (info->invert & ~1)
 		return -EINVAL;
 
+	if (!possible_classid(info->id)) {
+		pr_info("xt_cgroup: invalid classid\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -51,6 +64,11 @@ static int cgroup_mt_check_v1(const struct xt_mtchk_param *par)
 		return -EINVAL;
 	}
 
+	if (!possible_classid(info->classid)) {
+		pr_info("xt_cgroup: invalid classid\n");
+		return -EINVAL;
+	}
+
 	info->priv = NULL;
 	if (info->has_path) {
 		cgrp = cgroup_get_from_path(info->path);
@@ -83,6 +101,11 @@ static int cgroup_mt_check_v2(const struct xt_mtchk_param *par)
 		return -EINVAL;
 	}
 
+	if (info->has_classid && !possible_classid(info->classid)) {
+		pr_info("xt_cgroup: invalid classid\n");
+		return -EINVAL;
+	}
+
 	info->priv = NULL;
 	if (info->has_path) {
 		cgrp = cgroup_get_from_path(info->path);

base-commit: dd83757f6e686a2188997cb58b5975f744bb7786
-- 
2.48.1