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[PATCHSET v4] netfilter, cgroup: implement cgroup2 path match in xt_cgroup

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  [PATCHSET v4] netfilter, cgroup: implement cgroup2 path match in xt_cgroup Tejun Heo <tj@kernel.org> - 2015-12-07 23:40 +0100
    [PATCH 1/8] cgroup: record ancestor IDs and reimplement cgroup_is_descendant() using it Tejun Heo <tj@kernel.org> - 2015-12-07 23:50 +0100
    [PATCH 7/8] netfilter: prepare xt_cgroup for multi revisions Tejun Heo <tj@kernel.org> - 2015-12-07 23:50 +0100
    [PATCH 8/8] netfilter: implement xt_cgroup cgroup2 path match Tejun Heo <tj@kernel.org> - 2015-12-07 23:50 +0100
    [PATCH 6/8] sock, cgroup: add sock->sk_cgroup Tejun Heo <tj@kernel.org> - 2015-12-07 23:50 +0100
    [PATCH 3/8] cgroup: implement cgroup_get_from_path() and expose cgroup_put() Tejun Heo <tj@kernel.org> - 2015-12-07 23:50 +0100
    Re: [PATCHSET v4] netfilter, cgroup: implement cgroup2 path match  in xt_cgroup David Miller <davem@davemloft.net> - 2015-12-09 04:10 +0100

#1286048 — [PATCHSET v4] netfilter, cgroup: implement cgroup2 path match in xt_cgroup

Hello,

This is v4 of the xt_cgroup2 patchset.  Changes from v3 are

* Refreshed on top of net-next/master e72c932d3f8a ("cxgb3: Convert
  simple_strtoul to kstrtox").  Dropped "cgroups: Allow dynamically
  changing net_classid" from series as it's already applied.

The changes from v2 to v3 are

* Folded cgroup2 path matching into xt_cgroup as a new revision rather
  than a separate xt_cgroup2 match as suggested by Pablo.

* Refreshed on top of Nina's net_cls dynamic config update fix patch.
  I included the fix patch as part of this series to ease reviewing.

The changes from v1 to v2 are

* Instead of adding sock->sk_cgroup separately, sock->sk_cgrp_data now
  carries either (prioidx, classid) pair or cgroup2 pointer.  This
  avoids inflating struct sock with yet another cgroup related field.
  Unfortunately, this does add some complexity but that's the
  trade-off and the complexity is contained in cgroup proper.

* Various small updats as per David and Jan's reviews.


In cgroup v1, dealing with cgroup membership was difficult because the
number of membership associations was unbound.  As a result, cgroup v1
grew several controllers whose primary purpose is either tagging
membership or pull in configuration knobs from other subsystems so
that cgroup membership test can be avoided.

net_cls and net_prio controllers are examples of the latter.  They
allow configuring network-specific attributes from cgroup side so that
network subsystem can avoid testing cgroup membership; unfortunately,
these are not only cumbersome but also problematic.

Both net_cls and net_prio aren't properly hierarchical.  Both inherit
configuration from the parent on creation but there's no interaction
afterwards.  An ancestor doesn't restrict the behavior in its subtree
in anyway and configuration changes aren't propagated downwards.
Especially when combined with cgroup delegation, this is problematic
because delegatees can mess up whatever network configuration
implemented at the system level.  net_prio would allow the delegatees
to set whatever priority value regardless of CAP_NET_ADMIN and net_cls
the same for classid.

While it is possible to solve these issues from controller side by
implementing hierarchical allowable ranges in both controllers, it
would involve quite a bit of complexity in the controllers and further
obfuscate network configuration as it becomes even more difficult to
tell what's actually being configured looking from the network side.
While not much can be done for v1 at this point, as membership
handling is sane on cgroup v2, it'd be better to make cgroup matching
behave like other network matches and classifiers than introducing
further complications.

This patchset includes the following eight patches.

 0001-cgroup-record-ancestor-IDs-and-reimplement-cgroup_is.patch
 0002-kernfs-implement-kernfs_walk_and_get.patch
 0003-cgroup-implement-cgroup_get_from_path-and-expose-cgr.patch
 0004-netprio_cgroup-limit-the-maximum-css-id-to-USHRT_MAX.patch
 0005-net-wrap-sock-sk_cgrp_prioidx-and-sk_classid-inside-.patch
 0006-sock-cgroup-add-sock-sk_cgroup.patch
 0007-netfilter-prepare-xt_cgroup-for-multi-revisions.patch
 0008-netfilter-implement-xt_cgroup-cgroup2-path-match.patch

0001-0003 are prepatory patches in kernfs and cgroup.  These patches
are available in the following branch which will stay stable.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-4.5-ancestor-test

0004-0006 consolidate two cgroup related fields in struct sock into
cgroup_sock_data and update it so that it can alternatively carry a
cgroup pointer.

0007-0008 implement cgroup2 patch matching in xt_cgroup.

This patchset is on top of net-next/master and also available in the
following git branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-xt_cgroup2

I'll post iptables extension as a reply.  diffstat follows.  Thanks.

 fs/kernfs/dir.c                          |   46 +++++++++++
 include/linux/cgroup-defs.h              |  126 +++++++++++++++++++++++++++++++
 include/linux/cgroup.h                   |   66 +++++++++++++++-
 include/linux/kernfs.h                   |   12 ++
 include/net/cls_cgroup.h                 |   11 +-
 include/net/netprio_cgroup.h             |   16 +++
 include/net/sock.h                       |   13 ---
 include/uapi/linux/netfilter/xt_cgroup.h |   15 +++
 kernel/cgroup.c                          |  126 ++++++++++++++++++++++++-------
 net/Kconfig                              |    6 +
 net/core/dev.c                           |    3 
 net/core/netclassid_cgroup.c             |   11 +-
 net/core/netprio_cgroup.c                |   19 ++++
 net/core/scm.c                           |    4 
 net/core/sock.c                          |   17 ----
 net/netfilter/nft_meta.c                 |    2 
 net/netfilter/xt_cgroup.c                |  108 ++++++++++++++++++++++----
 17 files changed, 513 insertions(+), 88 deletions(-)

--
tejun
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#1286064 — [PATCH 1/8] cgroup: record ancestor IDs and reimplement cgroup_is_descendant() using it

cgroup_is_descendant() currently walks up the hierarchy and compares
each ancestor to the cgroup in question.  While enough for cgroup core
usages, this can't be used in hot paths to test cgroup membership.
This patch adds cgroup->ancestor_ids[] which records the IDs of all
ancestors including self and cgroup->level for the nesting level.

This allows testing whether a given cgroup is a descendant of another
in three finite steps - testing whether the two belong to the same
hierarchy, whether the descendant candidate is at the same or a higher
level than the ancestor and comparing the recorded ancestor_id at the
matching level.  cgroup_is_descendant() is accordingly reimplmented
and made inline.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 include/linux/cgroup-defs.h | 14 ++++++++++++++
 include/linux/cgroup.h      | 18 +++++++++++++++++-
 kernel/cgroup.c             | 32 ++++++++++----------------------
 3 files changed, 41 insertions(+), 23 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 60d44b2..504d859 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -235,6 +235,14 @@ struct cgroup {
 	int id;
 
 	/*
+	 * The depth this cgroup is at.  The root is at depth zero and each
+	 * step down the hierarchy increments the level.  This along with
+	 * ancestor_ids[] can determine whether a given cgroup is a
+	 * descendant of another without traversing the hierarchy.
+	 */
+	int level;
+
+	/*
 	 * Each non-empty css_set associated with this cgroup contributes
 	 * one to populated_cnt.  All children with non-zero popuplated_cnt
 	 * of their own contribute one.  The count is zero iff there's no
@@ -289,6 +297,9 @@ struct cgroup {
 
 	/* used to schedule release agent */
 	struct work_struct release_agent_work;
+
+	/* ids of the ancestors at each level including self */
+	int ancestor_ids[];
 };
 
 /*
@@ -308,6 +319,9 @@ struct cgroup_root {
 	/* The root cgroup.  Root is destroyed on its release. */
 	struct cgroup cgrp;
 
+	/* for cgrp->ancestor_ids[0] */
+	int cgrp_ancestor_id_storage;
+
 	/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
 	atomic_t nr_cgrps;
 
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 22e3754..b5ee2c4 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -81,7 +81,6 @@ struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgroup,
 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
 						       struct cgroup_subsys *ss);
 
-bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
 
@@ -459,6 +458,23 @@ static inline struct cgroup *task_cgroup(struct task_struct *task,
 	return task_css(task, subsys_id)->cgroup;
 }
 
+/**
+ * cgroup_is_descendant - test ancestry
+ * @cgrp: the cgroup to be tested
+ * @ancestor: possible ancestor of @cgrp
+ *
+ * Test whether @cgrp is a descendant of @ancestor.  It also returns %true
+ * if @cgrp == @ancestor.  This function is safe to call as long as @cgrp
+ * and @ancestor are accessible.
+ */
+static inline bool cgroup_is_descendant(struct cgroup *cgrp,
+					struct cgroup *ancestor)
+{
+	if (cgrp->root != ancestor->root || cgrp->level < ancestor->level)
+		return false;
+	return cgrp->ancestor_ids[ancestor->level] == ancestor->id;
+}
+
 /* no synchronization, the result can only be used as a hint */
 static inline bool cgroup_is_populated(struct cgroup *cgrp)
 {
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f1603c1..3190040 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -459,25 +459,6 @@ struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 }
 EXPORT_SYMBOL_GPL(of_css);
 
-/**
- * cgroup_is_descendant - test ancestry
- * @cgrp: the cgroup to be tested
- * @ancestor: possible ancestor of @cgrp
- *
- * Test whether @cgrp is a descendant of @ancestor.  It also returns %true
- * if @cgrp == @ancestor.  This function is safe to call as long as @cgrp
- * and @ancestor are accessible.
- */
-bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
-{
-	while (cgrp) {
-		if (cgrp == ancestor)
-			return true;
-		cgrp = cgroup_parent(cgrp);
-	}
-	return false;
-}
-
 static int notify_on_release(const struct cgroup *cgrp)
 {
 	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
@@ -1903,6 +1884,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
 	if (ret < 0)
 		goto out;
 	root_cgrp->id = ret;
+	root_cgrp->ancestor_ids[0] = ret;
 
 	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
 			      GFP_KERNEL);
@@ -4846,11 +4828,11 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
 static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 			umode_t mode)
 {
-	struct cgroup *parent, *cgrp;
+	struct cgroup *parent, *cgrp, *tcgrp;
 	struct cgroup_root *root;
 	struct cgroup_subsys *ss;
 	struct kernfs_node *kn;
-	int ssid, ret;
+	int level, ssid, ret;
 
 	/* Do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable.
 	 */
@@ -4861,9 +4843,11 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 	if (!parent)
 		return -ENODEV;
 	root = parent->root;
+	level = parent->level + 1;
 
 	/* allocate the cgroup and its ID, 0 is reserved for the root */
-	cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
+	cgrp = kzalloc(sizeof(*cgrp) +
+		       sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
 	if (!cgrp) {
 		ret = -ENOMEM;
 		goto out_unlock;
@@ -4887,6 +4871,10 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 
 	cgrp->self.parent = &parent->self;
 	cgrp->root = root;
+	cgrp->level = level;
+
+	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp))
+		cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
 
 	if (notify_on_release(parent))
 		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
-- 
2.5.0

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#1286065 — [PATCH 7/8] netfilter: prepare xt_cgroup for multi revisions

xt_cgroup will grow cgroup2 path based match.  Postfix existing
symbols with _v0 and prepare for multi revision registration.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Daniel Wagner <daniel.wagner@bmw-carit.de>
CC: Neil Horman <nhorman@tuxdriver.com>
Cc: Jan Engelhardt <jengelh@inai.de>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
---
 include/uapi/linux/netfilter/xt_cgroup.h |  2 +-
 net/netfilter/xt_cgroup.c                | 36 +++++++++++++++++---------------
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/include/uapi/linux/netfilter/xt_cgroup.h b/include/uapi/linux/netfilter/xt_cgroup.h
index 43acb7e..577c9e0 100644
--- a/include/uapi/linux/netfilter/xt_cgroup.h
+++ b/include/uapi/linux/netfilter/xt_cgroup.h
@@ -3,7 +3,7 @@
 
 #include <linux/types.h>
 
-struct xt_cgroup_info {
+struct xt_cgroup_info_v0 {
 	__u32 id;
 	__u32 invert;
 };
diff --git a/net/netfilter/xt_cgroup.c b/net/netfilter/xt_cgroup.c
index 54eaeb4..1730025 100644
--- a/net/netfilter/xt_cgroup.c
+++ b/net/netfilter/xt_cgroup.c
@@ -24,9 +24,9 @@ MODULE_DESCRIPTION("Xtables: process control group matching");
 MODULE_ALIAS("ipt_cgroup");
 MODULE_ALIAS("ip6t_cgroup");
 
-static int cgroup_mt_check(const struct xt_mtchk_param *par)
+static int cgroup_mt_check_v0(const struct xt_mtchk_param *par)
 {
-	struct xt_cgroup_info *info = par->matchinfo;
+	struct xt_cgroup_info_v0 *info = par->matchinfo;
 
 	if (info->invert & ~1)
 		return -EINVAL;
@@ -35,9 +35,9 @@ static int cgroup_mt_check(const struct xt_mtchk_param *par)
 }
 
 static bool
-cgroup_mt(const struct sk_buff *skb, struct xt_action_param *par)
+cgroup_mt_v0(const struct sk_buff *skb, struct xt_action_param *par)
 {
-	const struct xt_cgroup_info *info = par->matchinfo;
+	const struct xt_cgroup_info_v0 *info = par->matchinfo;
 
 	if (skb->sk == NULL || !sk_fullsock(skb->sk))
 		return false;
@@ -46,27 +46,29 @@ cgroup_mt(const struct sk_buff *skb, struct xt_action_param *par)
 		info->invert;
 }
 
-static struct xt_match cgroup_mt_reg __read_mostly = {
-	.name       = "cgroup",
-	.revision   = 0,
-	.family     = NFPROTO_UNSPEC,
-	.checkentry = cgroup_mt_check,
-	.match      = cgroup_mt,
-	.matchsize  = sizeof(struct xt_cgroup_info),
-	.me         = THIS_MODULE,
-	.hooks      = (1 << NF_INET_LOCAL_OUT) |
-		      (1 << NF_INET_POST_ROUTING) |
-		      (1 << NF_INET_LOCAL_IN),
+static struct xt_match cgroup_mt_reg[] __read_mostly = {
+	{
+		.name		= "cgroup",
+		.revision	= 0,
+		.family		= NFPROTO_UNSPEC,
+		.checkentry	= cgroup_mt_check_v0,
+		.match		= cgroup_mt_v0,
+		.matchsize	= sizeof(struct xt_cgroup_info_v0),
+		.me		= THIS_MODULE,
+		.hooks		= (1 << NF_INET_LOCAL_OUT) |
+				  (1 << NF_INET_POST_ROUTING) |
+				  (1 << NF_INET_LOCAL_IN),
+	},
 };
 
 static int __init cgroup_mt_init(void)
 {
-	return xt_register_match(&cgroup_mt_reg);
+	return xt_register_matches(cgroup_mt_reg, ARRAY_SIZE(cgroup_mt_reg));
 }
 
 static void __exit cgroup_mt_exit(void)
 {
-	xt_unregister_match(&cgroup_mt_reg);
+	xt_unregister_matches(cgroup_mt_reg, ARRAY_SIZE(cgroup_mt_reg));
 }
 
 module_init(cgroup_mt_init);
-- 
2.5.0

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#1286066 — [PATCH 8/8] netfilter: implement xt_cgroup cgroup2 path match

This patch implements xt_cgroup path match which matches cgroup2
membership of the associated socket.  The match is recursive and
invertible.

For rationales on introducing another cgroup based match, please refer
to a preceding commit "sock, cgroup: add sock->sk_cgroup".

v3: Folded into xt_cgroup as a new revision interface as suggested by
    Pablo.

v2: Included linux/limits.h from xt_cgroup2.h for PATH_MAX.  Added
    explicit alignment to the priv field.  Both suggested by Jan.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Daniel Wagner <daniel.wagner@bmw-carit.de>
CC: Neil Horman <nhorman@tuxdriver.com>
Cc: Jan Engelhardt <jengelh@inai.de>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
---
 include/uapi/linux/netfilter/xt_cgroup.h | 13 ++++++
 net/netfilter/xt_cgroup.c                | 69 ++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)

diff --git a/include/uapi/linux/netfilter/xt_cgroup.h b/include/uapi/linux/netfilter/xt_cgroup.h
index 577c9e0..1e4b37b 100644
--- a/include/uapi/linux/netfilter/xt_cgroup.h
+++ b/include/uapi/linux/netfilter/xt_cgroup.h
@@ -2,10 +2,23 @@
 #define _UAPI_XT_CGROUP_H
 
 #include <linux/types.h>
+#include <linux/limits.h>
 
 struct xt_cgroup_info_v0 {
 	__u32 id;
 	__u32 invert;
 };
 
+struct xt_cgroup_info_v1 {
+	__u8		has_path;
+	__u8		has_classid;
+	__u8		invert_path;
+	__u8		invert_classid;
+	char		path[PATH_MAX];
+	__u32		classid;
+
+	/* kernel internal data */
+	void		*priv __attribute__((aligned(8)));
+};
+
 #endif /* _UAPI_XT_CGROUP_H */
diff --git a/net/netfilter/xt_cgroup.c b/net/netfilter/xt_cgroup.c
index 1730025..a086a91 100644
--- a/net/netfilter/xt_cgroup.c
+++ b/net/netfilter/xt_cgroup.c
@@ -34,6 +34,37 @@ static int cgroup_mt_check_v0(const struct xt_mtchk_param *par)
 	return 0;
 }
 
+static int cgroup_mt_check_v1(const struct xt_mtchk_param *par)
+{
+	struct xt_cgroup_info_v1 *info = par->matchinfo;
+	struct cgroup *cgrp;
+
+	if ((info->invert_path & ~1) || (info->invert_classid & ~1))
+		return -EINVAL;
+
+	if (!info->has_path && !info->has_classid) {
+		pr_info("xt_cgroup: no path or classid specified\n");
+		return -EINVAL;
+	}
+
+	if (info->has_path && info->has_classid) {
+		pr_info("xt_cgroup: both path and classid specified\n");
+		return -EINVAL;
+	}
+
+	if (info->has_path) {
+		cgrp = cgroup_get_from_path(info->path);
+		if (IS_ERR(cgrp)) {
+			pr_info("xt_cgroup: invalid path, errno=%ld\n",
+				PTR_ERR(cgrp));
+			return -EINVAL;
+		}
+		info->priv = cgrp;
+	}
+
+	return 0;
+}
+
 static bool
 cgroup_mt_v0(const struct sk_buff *skb, struct xt_action_param *par)
 {
@@ -46,6 +77,31 @@ cgroup_mt_v0(const struct sk_buff *skb, struct xt_action_param *par)
 		info->invert;
 }
 
+static bool cgroup_mt_v1(const struct sk_buff *skb, struct xt_action_param *par)
+{
+	const struct xt_cgroup_info_v1 *info = par->matchinfo;
+	struct sock_cgroup_data *skcd = &skb->sk->sk_cgrp_data;
+	struct cgroup *ancestor = info->priv;
+
+	if (!skb->sk || !sk_fullsock(skb->sk))
+		return false;
+
+	if (ancestor)
+		return cgroup_is_descendant(sock_cgroup_ptr(skcd), ancestor) ^
+			info->invert_path;
+	else
+		return (info->classid == sock_cgroup_classid(skcd)) ^
+			info->invert_classid;
+}
+
+static void cgroup_mt_destroy_v1(const struct xt_mtdtor_param *par)
+{
+	struct xt_cgroup_info_v1 *info = par->matchinfo;
+
+	if (info->priv)
+		cgroup_put(info->priv);
+}
+
 static struct xt_match cgroup_mt_reg[] __read_mostly = {
 	{
 		.name		= "cgroup",
@@ -59,6 +115,19 @@ static struct xt_match cgroup_mt_reg[] __read_mostly = {
 				  (1 << NF_INET_POST_ROUTING) |
 				  (1 << NF_INET_LOCAL_IN),
 	},
+	{
+		.name		= "cgroup",
+		.revision	= 1,
+		.family		= NFPROTO_UNSPEC,
+		.checkentry	= cgroup_mt_check_v1,
+		.match		= cgroup_mt_v1,
+		.matchsize	= sizeof(struct xt_cgroup_info_v1),
+		.destroy	= cgroup_mt_destroy_v1,
+		.me		= THIS_MODULE,
+		.hooks		= (1 << NF_INET_LOCAL_OUT) |
+				  (1 << NF_INET_POST_ROUTING) |
+				  (1 << NF_INET_LOCAL_IN),
+	},
 };
 
 static int __init cgroup_mt_init(void)
-- 
2.5.0

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#1286067 — [PATCH 6/8] sock, cgroup: add sock->sk_cgroup

In cgroup v1, dealing with cgroup membership was difficult because the
number of membership associations was unbound.  As a result, cgroup v1
grew several controllers whose primary purpose is either tagging
membership or pull in configuration knobs from other subsystems so
that cgroup membership test can be avoided.

net_cls and net_prio controllers are examples of the latter.  They
allow configuring network-specific attributes from cgroup side so that
network subsystem can avoid testing cgroup membership; unfortunately,
these are not only cumbersome but also problematic.

Both net_cls and net_prio aren't properly hierarchical.  Both inherit
configuration from the parent on creation but there's no interaction
afterwards.  An ancestor doesn't restrict the behavior in its subtree
in anyway and configuration changes aren't propagated downwards.
Especially when combined with cgroup delegation, this is problematic
because delegatees can mess up whatever network configuration
implemented at the system level.  net_prio would allow the delegatees
to set whatever priority value regardless of CAP_NET_ADMIN and net_cls
the same for classid.

While it is possible to solve these issues from controller side by
implementing hierarchical allowable ranges in both controllers, it
would involve quite a bit of complexity in the controllers and further
obfuscate network configuration as it becomes even more difficult to
tell what's actually being configured looking from the network side.
While not much can be done for v1 at this point, as membership
handling is sane on cgroup v2, it'd be better to make cgroup matching
behave like other network matches and classifiers than introducing
further complications.

In preparation, this patch updates sock->sk_cgrp_data handling so that
it points to the v2 cgroup that sock was created in until either
net_prio or net_cls is used.  Once either of the two is used,
sock->sk_cgrp_data reverts to its previous role of carrying prioidx
and classid.  This is to avoid adding yet another cgroup related field
to struct sock.

As the mode switching can happen at most once per boot, the switching
mechanism is aimed at lowering hot path overhead.  It may leak a
finite, likely small, number of cgroup refs and report spurious
prioidx or classid on switching; however, dynamic updates of prioidx
and classid have always been racy and lossy - socks between creation
and fd installation are never updated, config changes don't update
existing sockets at all, and prioidx may index with dead and recycled
cgroup IDs.  Non-critical inaccuracies from small race windows won't
make any noticeable difference.

This patch doesn't make use of the pointer yet.  The following patch
will implement netfilter match for cgroup2 membership.

v2: Use sock_cgroup_data to avoid inflating struct sock w/ another
    cgroup specific field.

v3: Add comments explaining why sock_data_prioidx() and
    sock_data_classid() use different fallback values.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Daniel Wagner <daniel.wagner@bmw-carit.de>
CC: Neil Horman <nhorman@tuxdriver.com>
---
 include/linux/cgroup-defs.h  | 88 +++++++++++++++++++++++++++++++++++++++++---
 include/linux/cgroup.h       | 41 +++++++++++++++++++++
 kernel/cgroup.c              | 55 ++++++++++++++++++++++++++-
 net/core/netclassid_cgroup.c |  7 +++-
 net/core/netprio_cgroup.c    |  7 +++-
 net/core/sock.c              |  2 +
 6 files changed, 191 insertions(+), 9 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index ed128fed..9dc2263 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -544,31 +544,107 @@ static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}
 
 #ifdef CONFIG_SOCK_CGROUP_DATA
 
+/*
+ * sock_cgroup_data is embedded at sock->sk_cgrp_data and contains
+ * per-socket cgroup information except for memcg association.
+ *
+ * On legacy hierarchies, net_prio and net_cls controllers directly set
+ * attributes on each sock which can then be tested by the network layer.
+ * On the default hierarchy, each sock is associated with the cgroup it was
+ * created in and the networking layer can match the cgroup directly.
+ *
+ * To avoid carrying all three cgroup related fields separately in sock,
+ * sock_cgroup_data overloads (prioidx, classid) and the cgroup pointer.
+ * On boot, sock_cgroup_data records the cgroup that the sock was created
+ * in so that cgroup2 matches can be made; however, once either net_prio or
+ * net_cls starts being used, the area is overriden to carry prioidx and/or
+ * classid.  The two modes are distinguished by whether the lowest bit is
+ * set.  Clear bit indicates cgroup pointer while set bit prioidx and
+ * classid.
+ *
+ * While userland may start using net_prio or net_cls at any time, once
+ * either is used, cgroup2 matching no longer works.  There is no reason to
+ * mix the two and this is in line with how legacy and v2 compatibility is
+ * handled.  On mode switch, cgroup references which are already being
+ * pointed to by socks may be leaked.  While this can be remedied by adding
+ * synchronization around sock_cgroup_data, given that the number of leaked
+ * cgroups is bound and highly unlikely to be high, this seems to be the
+ * better trade-off.
+ */
 struct sock_cgroup_data {
-	u16	prioidx;
-	u32	classid;
+	union {
+#ifdef __LITTLE_ENDIAN
+		struct {
+			u8	is_data;
+			u8	padding;
+			u16	prioidx;
+			u32	classid;
+		} __packed;
+#else
+		struct {
+			u32	classid;
+			u16	prioidx;
+			u8	padding;
+			u8	is_data;
+		} __packed;
+#endif
+		u64		val;
+	};
 };
 
+/*
+ * There's a theoretical window where the following accessors race with
+ * updaters and return part of the previous pointer as the prioidx or
+ * classid.  Such races are short-lived and the result isn't critical.
+ */
 static inline u16 sock_cgroup_prioidx(struct sock_cgroup_data *skcd)
 {
-	return skcd->prioidx;
+	/* fallback to 1 which is always the ID of the root cgroup */
+	return (skcd->is_data & 1) ? skcd->prioidx : 1;
 }
 
 static inline u32 sock_cgroup_classid(struct sock_cgroup_data *skcd)
 {
-	return skcd->classid;
+	/* fallback to 0 which is the unconfigured default classid */
+	return (skcd->is_data & 1) ? skcd->classid : 0;
 }
 
+/*
+ * If invoked concurrently, the updaters may clobber each other.  The
+ * caller is responsible for synchronization.
+ */
 static inline void sock_cgroup_set_prioidx(struct sock_cgroup_data *skcd,
 					   u16 prioidx)
 {
-	skcd->prioidx = prioidx;
+	struct sock_cgroup_data skcd_buf = { .val = READ_ONCE(skcd->val) };
+
+	if (sock_cgroup_prioidx(&skcd_buf) == prioidx)
+		return;
+
+	if (!(skcd_buf.is_data & 1)) {
+		skcd_buf.val = 0;
+		skcd_buf.is_data = 1;
+	}
+
+	skcd_buf.prioidx = prioidx;
+	WRITE_ONCE(skcd->val, skcd_buf.val);	/* see sock_cgroup_ptr() */
 }
 
 static inline void sock_cgroup_set_classid(struct sock_cgroup_data *skcd,
 					   u32 classid)
 {
-	skcd->classid = classid;
+	struct sock_cgroup_data skcd_buf = { .val = READ_ONCE(skcd->val) };
+
+	if (sock_cgroup_classid(&skcd_buf) == classid)
+		return;
+
+	if (!(skcd_buf.is_data & 1)) {
+		skcd_buf.val = 0;
+		skcd_buf.is_data = 1;
+	}
+
+	skcd_buf.classid = classid;
+	WRITE_ONCE(skcd->val, skcd_buf.val);	/* see sock_cgroup_ptr() */
 }
 
 #else	/* CONFIG_SOCK_CGROUP_DATA */
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 4c3ffab..a8ba1ea 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -578,4 +578,45 @@ static inline int cgroup_init(void) { return 0; }
 
 #endif /* !CONFIG_CGROUPS */
 
+/*
+ * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
+ * definition in cgroup-defs.h.
+ */
+#ifdef CONFIG_SOCK_CGROUP_DATA
+
+#if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
+extern spinlock_t cgroup_sk_update_lock;
+#endif
+
+void cgroup_sk_alloc_disable(void);
+void cgroup_sk_alloc(struct sock_cgroup_data *skcd);
+void cgroup_sk_free(struct sock_cgroup_data *skcd);
+
+static inline struct cgroup *sock_cgroup_ptr(struct sock_cgroup_data *skcd)
+{
+#if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
+	unsigned long v;
+
+	/*
+	 * @skcd->val is 64bit but the following is safe on 32bit too as we
+	 * just need the lower ulong to be written and read atomically.
+	 */
+	v = READ_ONCE(skcd->val);
+
+	if (v & 1)
+		return &cgrp_dfl_root.cgrp;
+
+	return (struct cgroup *)(unsigned long)v ?: &cgrp_dfl_root.cgrp;
+#else
+	return (struct cgroup *)(unsigned long)skcd->val;
+#endif
+}
+
+#else	/* CONFIG_CGROUP_DATA */
+
+static inline void cgroup_sk_alloc(struct sock_cgroup_data *skcd) {}
+static inline void cgroup_sk_free(struct sock_cgroup_data *skcd) {}
+
+#endif	/* CONFIG_CGROUP_DATA */
+
 #endif /* _LINUX_CGROUP_H */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3db5e8f..4f8f792 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -57,8 +57,8 @@
 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
 #include <linux/kthread.h>
 #include <linux/delay.h>
-
 #include <linux/atomic.h>
+#include <net/sock.h>
 
 /*
  * pidlists linger the following amount before being destroyed.  The goal
@@ -5782,6 +5782,59 @@ struct cgroup *cgroup_get_from_path(const char *path)
 }
 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
 
+/*
+ * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
+ * definition in cgroup-defs.h.
+ */
+#ifdef CONFIG_SOCK_CGROUP_DATA
+
+#if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
+
+spinlock_t cgroup_sk_update_lock;
+static bool cgroup_sk_alloc_disabled __read_mostly;
+
+void cgroup_sk_alloc_disable(void)
+{
+	if (cgroup_sk_alloc_disabled)
+		return;
+	pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
+	cgroup_sk_alloc_disabled = true;
+}
+
+#else
+
+#define cgroup_sk_alloc_disabled	false
+
+#endif
+
+void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
+{
+	if (cgroup_sk_alloc_disabled)
+		return;
+
+	rcu_read_lock();
+
+	while (true) {
+		struct css_set *cset;
+
+		cset = task_css_set(current);
+		if (likely(cgroup_tryget(cset->dfl_cgrp))) {
+			skcd->val = (unsigned long)cset->dfl_cgrp;
+			break;
+		}
+		cpu_relax();
+	}
+
+	rcu_read_unlock();
+}
+
+void cgroup_sk_free(struct sock_cgroup_data *skcd)
+{
+	cgroup_put(sock_cgroup_ptr(skcd));
+}
+
+#endif	/* CONFIG_SOCK_CGROUP_DATA */
+
 #ifdef CONFIG_CGROUP_DEBUG
 static struct cgroup_subsys_state *
 debug_css_alloc(struct cgroup_subsys_state *parent_css)
diff --git a/net/core/netclassid_cgroup.c b/net/core/netclassid_cgroup.c
index e60ded4..04257a0 100644
--- a/net/core/netclassid_cgroup.c
+++ b/net/core/netclassid_cgroup.c
@@ -61,9 +61,12 @@ static int update_classid_sock(const void *v, struct file *file, unsigned n)
 	int err;
 	struct socket *sock = sock_from_file(file, &err);
 
-	if (sock)
+	if (sock) {
+		spin_lock(&cgroup_sk_update_lock);
 		sock_cgroup_set_classid(&sock->sk->sk_cgrp_data,
 					(unsigned long)v);
+		spin_unlock(&cgroup_sk_update_lock);
+	}
 	return 0;
 }
 
@@ -98,6 +101,8 @@ static int write_classid(struct cgroup_subsys_state *css, struct cftype *cft,
 {
 	struct cgroup_cls_state *cs = css_cls_state(css);
 
+	cgroup_sk_alloc_disable();
+
 	cs->classid = (u32)value;
 
 	update_classid(css, (void *)(unsigned long)cs->classid);
diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index de42aa7..053d60c 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -209,6 +209,8 @@ static ssize_t write_priomap(struct kernfs_open_file *of,
 	if (!dev)
 		return -ENODEV;
 
+	cgroup_sk_alloc_disable();
+
 	rtnl_lock();
 
 	ret = netprio_set_prio(of_css(of), dev, prio);
@@ -222,9 +224,12 @@ static int update_netprio(const void *v, struct file *file, unsigned n)
 {
 	int err;
 	struct socket *sock = sock_from_file(file, &err);
-	if (sock)
+	if (sock) {
+		spin_lock(&cgroup_sk_update_lock);
 		sock_cgroup_set_prioidx(&sock->sk->sk_cgrp_data,
 					(unsigned long)v);
+		spin_unlock(&cgroup_sk_update_lock);
+	}
 	return 0;
 }
 
diff --git a/net/core/sock.c b/net/core/sock.c
index 947741d..1278d7b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1363,6 +1363,7 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
 		if (!try_module_get(prot->owner))
 			goto out_free_sec;
 		sk_tx_queue_clear(sk);
+		cgroup_sk_alloc(&sk->sk_cgrp_data);
 	}
 
 	return sk;
@@ -1385,6 +1386,7 @@ static void sk_prot_free(struct proto *prot, struct sock *sk)
 	owner = prot->owner;
 	slab = prot->slab;
 
+	cgroup_sk_free(&sk->sk_cgrp_data);
 	security_sk_free(sk);
 	if (slab != NULL)
 		kmem_cache_free(slab, sk);
-- 
2.5.0

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#1286072 — [PATCH 3/8] cgroup: implement cgroup_get_from_path() and expose cgroup_put()

Implement cgroup_get_from_path() using kernfs_walk_and_get() which
obtains a default hierarchy cgroup from its path.  This will be used
to allow cgroup path based matching from outside cgroup proper -
e.g. networking and perf.

v2: Add EXPORT_SYMBOL_GPL(cgroup_get_from_path).

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 include/linux/cgroup.h |  7 +++++++
 kernel/cgroup.c        | 39 ++++++++++++++++++++++++++++++++++-----
 2 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b5ee2c4..4c3ffab 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -81,6 +81,8 @@ struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgroup,
 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
 						       struct cgroup_subsys *ss);
 
+struct cgroup *cgroup_get_from_path(const char *path);
+
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
 
@@ -351,6 +353,11 @@ static inline void css_put_many(struct cgroup_subsys_state *css, unsigned int n)
 		percpu_ref_put_many(&css->refcnt, n);
 }
 
+static inline void cgroup_put(struct cgroup *cgrp)
+{
+	css_put(&cgrp->self);
+}
+
 /**
  * task_css_set_check - obtain a task's css_set with extra access conditions
  * @task: the task to obtain css_set for
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3190040..3db5e8f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -434,11 +434,6 @@ static bool cgroup_tryget(struct cgroup *cgrp)
 	return css_tryget(&cgrp->self);
 }
 
-static void cgroup_put(struct cgroup *cgrp)
-{
-	css_put(&cgrp->self);
-}
-
 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 {
 	struct cgroup *cgrp = of->kn->parent->priv;
@@ -5753,6 +5748,40 @@ struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
 	return id > 0 ? idr_find(&ss->css_idr, id) : NULL;
 }
 
+/**
+ * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
+ * @path: path on the default hierarchy
+ *
+ * Find the cgroup at @path on the default hierarchy, increment its
+ * reference count and return it.  Returns pointer to the found cgroup on
+ * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
+ * if @path points to a non-directory.
+ */
+struct cgroup *cgroup_get_from_path(const char *path)
+{
+	struct kernfs_node *kn;
+	struct cgroup *cgrp;
+
+	mutex_lock(&cgroup_mutex);
+
+	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
+	if (kn) {
+		if (kernfs_type(kn) == KERNFS_DIR) {
+			cgrp = kn->priv;
+			cgroup_get(cgrp);
+		} else {
+			cgrp = ERR_PTR(-ENOTDIR);
+		}
+		kernfs_put(kn);
+	} else {
+		cgrp = ERR_PTR(-ENOENT);
+	}
+
+	mutex_unlock(&cgroup_mutex);
+	return cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_get_from_path);
+
 #ifdef CONFIG_CGROUP_DEBUG
 static struct cgroup_subsys_state *
 debug_css_alloc(struct cgroup_subsys_state *parent_css)
-- 
2.5.0

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#1287040 — Re: [PATCHSET v4] netfilter, cgroup: implement cgroup2 path match in xt_cgroup

From: Tejun Heo <tj@kernel.org>
Date: Mon,  7 Dec 2015 17:38:47 -0500

> 0001-0003 are prepatory patches in kernfs and cgroup.  These patches
> are available in the following branch which will stay stable.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-4.5-ancestor-test

Pulled into net-next.

> 0004-0006 consolidate two cgroup related fields in struct sock into
> cgroup_sock_data and update it so that it can alternatively carry a
> cgroup pointer.

Applied to net-next.

> 0007-0008 implement cgroup2 patch matching in xt_cgroup.

I'll leave these for Pablo to integrate.

Thanks.
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