[PATCH nf 2/2] netfilter: nft_socket: make cgroupsv2 matching work with namespaces

[PATCH nf 2/2] netfilter: nft_socket: make cgroupsv2 matching work with namespaces

[Florian Westphal]

When running in container environmment, /sys/fs/cgroup/ might not be
the real root node of the sk-attached cgroup.

Example:

In container:
% stat /sys//fs/cgroup/
Device: 0,21    Inode: 2214  ..
% stat /sys/fs/cgroup/foo
Device: 0,21    Inode: 2264  ..

The expectation would be for:

  nft add rule .. socket cgroupv2 level 1 "foo" counter

to match traffic from a process that got added to "foo" via
"echo $pid > /sys/fs/cgroup/foo/cgroup.procs".

However, 'level 3' is needed to make this work.

Seen from initial namespace, the complete hierarchy is:

% stat /sys/fs/cgroup/system.slice/docker-.../foo
  Device: 0,21    Inode: 2264 ..

i.e. hierarchy is
0    1               2              3
/ -> system.slice -> docker-1... -> foo

... but the container doesn't know that its "/" is the "docker-1.."
cgroup.  Current code will retrieve the 'system.slice' cgroup node
and store its kn->id in the destination register, so compare with
2264 ("foo" cgroup id) will not match.

Fetch "/" cgroup from ->init() and add its level to the level we try to
extract.  cgroup root-level is 0 for the init-namespace or the level
of the ancestor that is exposed as the cgroup root inside the container.

In the above case, cgrp->level of "/" resolved in the container is 2
(docker-1...scope/) and request for 'level 1' will get adjusted
to fetch the actual level (3).

Cc: cgroups@vger.kernel.org
Fixes: e0bb96db96f8 ("netfilter: nft_socket: add support for cgroupsv2")
Reported-by: Nadia Pinaeva <n.m.pinaeva@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_socket.c | 39 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nft_socket.c b/net/netfilter/nft_socket.c
index 765ffd6e06bc..0e8367c8f280 100644
--- a/net/netfilter/nft_socket.c
+++ b/net/netfilter/nft_socket.c
@@ -9,7 +9,8 @@
 
 struct nft_socket {
 	enum nft_socket_keys		key:8;
-	u8				level;
+	u8				level;		/* cgroupv2 level to extract */
+	u8				level_user;	/* cgroupv2 level provided by userspace */
 	u8				len;
 	union {
 		u8			dreg;
@@ -53,6 +54,28 @@ nft_sock_get_eval_cgroupv2(u32 *dest, struct sock *sk, const struct nft_pktinfo
 	memcpy(dest, &cgid, sizeof(u64));
 	return true;
 }
+
+/* process context only, uses current->nsproxy. */
+static noinline int nft_socket_cgroup_subtree_level(void)
+{
+	struct cgroup *cgrp = cgroup_get_from_path("/");
+	int level;
+
+	if (!cgrp)
+		return -ENOENT;
+
+	level = cgrp->level;
+
+	cgroup_put(cgrp);
+
+	if (WARN_ON_ONCE(level > 255))
+		return -ERANGE;
+
+	if (WARN_ON_ONCE(level < 0))
+		return -EINVAL;
+
+	return level;
+}
 #endif
 
 static struct sock *nft_socket_do_lookup(const struct nft_pktinfo *pkt)
@@ -177,6 +200,7 @@ static int nft_socket_init(const struct nft_ctx *ctx,
 #ifdef CONFIG_CGROUPS
 	case NFT_SOCKET_CGROUPV2: {
 		unsigned int level;
+		int err;
 
 		if (!tb[NFTA_SOCKET_LEVEL])
 			return -EINVAL;
@@ -185,6 +209,17 @@ static int nft_socket_init(const struct nft_ctx *ctx,
 		if (level > 255)
 			return -EOPNOTSUPP;
 
+		err = nft_socket_cgroup_subtree_level();
+		if (err < 0)
+			return err;
+
+		priv->level_user = level;
+
+		level += err;
+		/* Implies a giant cgroup tree */
+		if (WARN_ON_ONCE(level > 255))
+			return -EOPNOTSUPP;
+
 		priv->level = level;
 		len = sizeof(u64);
 		break;
@@ -209,7 +244,7 @@ static int nft_socket_dump(struct sk_buff *skb,
 	if (nft_dump_register(skb, NFTA_SOCKET_DREG, priv->dreg))
 		return -1;
 	if (priv->key == NFT_SOCKET_CGROUPV2 &&
-	    nla_put_be32(skb, NFTA_SOCKET_LEVEL, htonl(priv->level)))
+	    nla_put_be32(skb, NFTA_SOCKET_LEVEL, htonl(priv->level_user)))
 		return -1;
 	return 0;
 }
-- 
2.44.2

Re: [PATCH nf 2/2] netfilter: nft_socket: make cgroupsv2 matching work with namespaces

[kernel test robot]

Hi Florian,

kernel test robot noticed the following build errors:

[auto build test ERROR on netfilter-nf/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Florian-Westphal/netfilter-nft_socket-make-cgroupsv2-matching-work-with-namespaces/20240905-185930
base:   https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf.git main
patch link:    https://lore.kernel.org/r/20240905105451.28857-2-fw%40strlen.de
patch subject: [PATCH nf 2/2] netfilter: nft_socket: make cgroupsv2 matching work with namespaces
config: arm-randconfig-002-20240907 (https://download.01.org/0day-ci/archive/20240907/202409070305.pBDk8EVS-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 14.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240907/202409070305.pBDk8EVS-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409070305.pBDk8EVS-lkp@intel.com/

All errors (new ones prefixed by >>):

   net/netfilter/nft_socket.c: In function 'nft_socket_init':
>> net/netfilter/nft_socket.c:212:23: error: implicit declaration of function 'nft_socket_cgroup_subtree_level' [-Wimplicit-function-declaration]
     212 |                 err = nft_socket_cgroup_subtree_level();
         |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/nft_socket_cgroup_subtree_level +212 net/netfilter/nft_socket.c

   169	
   170	static int nft_socket_init(const struct nft_ctx *ctx,
   171				   const struct nft_expr *expr,
   172				   const struct nlattr * const tb[])
   173	{
   174		struct nft_socket *priv = nft_expr_priv(expr);
   175		unsigned int len;
   176	
   177		if (!tb[NFTA_SOCKET_DREG] || !tb[NFTA_SOCKET_KEY])
   178			return -EINVAL;
   179	
   180		switch(ctx->family) {
   181		case NFPROTO_IPV4:
   182	#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
   183		case NFPROTO_IPV6:
   184	#endif
   185		case NFPROTO_INET:
   186			break;
   187		default:
   188			return -EOPNOTSUPP;
   189		}
   190	
   191		priv->key = ntohl(nla_get_be32(tb[NFTA_SOCKET_KEY]));
   192		switch(priv->key) {
   193		case NFT_SOCKET_TRANSPARENT:
   194		case NFT_SOCKET_WILDCARD:
   195			len = sizeof(u8);
   196			break;
   197		case NFT_SOCKET_MARK:
   198			len = sizeof(u32);
   199			break;
   200	#ifdef CONFIG_CGROUPS
   201		case NFT_SOCKET_CGROUPV2: {
   202			unsigned int level;
   203			int err;
   204	
   205			if (!tb[NFTA_SOCKET_LEVEL])
   206				return -EINVAL;
   207	
   208			level = ntohl(nla_get_be32(tb[NFTA_SOCKET_LEVEL]));
   209			if (level > 255)
   210				return -EOPNOTSUPP;
   211	
 > 212			err = nft_socket_cgroup_subtree_level();
   213			if (err < 0)
   214				return err;
   215	
   216			priv->level_user = level;
   217	
   218			level += err;
   219			/* Implies a giant cgroup tree */
   220			if (WARN_ON_ONCE(level > 255))
   221				return -EOPNOTSUPP;
   222	
   223			priv->level = level;
   224			len = sizeof(u64);
   225			break;
   226		}
   227	#endif
   228		default:
   229			return -EOPNOTSUPP;
   230		}
   231	
   232		priv->len = len;
   233		return nft_parse_register_store(ctx, tb[NFTA_SOCKET_DREG], &priv->dreg,
   234						NULL, NFT_DATA_VALUE, len);
   235	}
   236	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH nf 2/2] netfilter: nft_socket: make cgroupsv2 matching work with namespaces

[kernel test robot]

Hi Florian,

kernel test robot noticed the following build errors:

[auto build test ERROR on netfilter-nf/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Florian-Westphal/netfilter-nft_socket-make-cgroupsv2-matching-work-with-namespaces/20240908-025647
base:   https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf.git main
patch link:    https://lore.kernel.org/r/20240905105451.28857-2-fw%40strlen.de
patch subject: [PATCH nf 2/2] netfilter: nft_socket: make cgroupsv2 matching work with namespaces
config: i386-randconfig-006-20240908 (https://download.01.org/0day-ci/archive/20240909/202409090022.jxFbbVYj-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240909/202409090022.jxFbbVYj-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409090022.jxFbbVYj-lkp@intel.com/

All errors (new ones prefixed by >>):

>> net/netfilter/nft_socket.c:212:9: error: call to undeclared function 'nft_socket_cgroup_subtree_level'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     212 |                 err = nft_socket_cgroup_subtree_level();
         |                       ^
   1 error generated.


vim +/nft_socket_cgroup_subtree_level +212 net/netfilter/nft_socket.c

   169	
   170	static int nft_socket_init(const struct nft_ctx *ctx,
   171				   const struct nft_expr *expr,
   172				   const struct nlattr * const tb[])
   173	{
   174		struct nft_socket *priv = nft_expr_priv(expr);
   175		unsigned int len;
   176	
   177		if (!tb[NFTA_SOCKET_DREG] || !tb[NFTA_SOCKET_KEY])
   178			return -EINVAL;
   179	
   180		switch(ctx->family) {
   181		case NFPROTO_IPV4:
   182	#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
   183		case NFPROTO_IPV6:
   184	#endif
   185		case NFPROTO_INET:
   186			break;
   187		default:
   188			return -EOPNOTSUPP;
   189		}
   190	
   191		priv->key = ntohl(nla_get_be32(tb[NFTA_SOCKET_KEY]));
   192		switch(priv->key) {
   193		case NFT_SOCKET_TRANSPARENT:
   194		case NFT_SOCKET_WILDCARD:
   195			len = sizeof(u8);
   196			break;
   197		case NFT_SOCKET_MARK:
   198			len = sizeof(u32);
   199			break;
   200	#ifdef CONFIG_CGROUPS
   201		case NFT_SOCKET_CGROUPV2: {
   202			unsigned int level;
   203			int err;
   204	
   205			if (!tb[NFTA_SOCKET_LEVEL])
   206				return -EINVAL;
   207	
   208			level = ntohl(nla_get_be32(tb[NFTA_SOCKET_LEVEL]));
   209			if (level > 255)
   210				return -EOPNOTSUPP;
   211	
 > 212			err = nft_socket_cgroup_subtree_level();
   213			if (err < 0)
   214				return err;
   215	
   216			priv->level_user = level;
   217	
   218			level += err;
   219			/* Implies a giant cgroup tree */
   220			if (WARN_ON_ONCE(level > 255))
   221				return -EOPNOTSUPP;
   222	
   223			priv->level = level;
   224			len = sizeof(u64);
   225			break;
   226		}
   227	#endif
   228		default:
   229			return -EOPNOTSUPP;
   230		}
   231	
   232		priv->len = len;
   233		return nft_parse_register_store(ctx, tb[NFTA_SOCKET_DREG], &priv->dreg,
   234						NULL, NFT_DATA_VALUE, len);
   235	}
   236	

-- 
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