Merge branch 'for-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
Pull cgroup updates from Tejun Heo:
- a new PIDs controller is added. It turns out that PIDs are actually
an independent resource from kmem due to the limited PID space.
- more core preparations for the v2 interface. Once cpu side interface
is settled, it should be ready for lifting the devel mask.
for-4.3-unified-base was temporarily branched so that other trees
(block) can pull cgroup core changes that blkcg changes depend on.
- a non-critical idr_preload usage bug fix.
* 'for-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup: pids: fix invalid get/put usage
cgroup: introduce cgroup_subsys->legacy_name
cgroup: don't print subsystems for the default hierarchy
cgroup: make cftype->private a unsigned long
cgroup: export cgrp_dfl_root
cgroup: define controller file conventions
cgroup: fix idr_preload usage
cgroup: add documentation for the PIDs controller
cgroup: implement the PIDs subsystem
cgroup: allow a cgroup subsystem to reject a fork
diff --git a/CREDITS b/CREDITS
index 1d61664..4fcf9cd 100644
--- a/CREDITS
+++ b/CREDITS
@@ -3219,6 +3219,11 @@
S: 75013 Paris
S: France
+N: Aleksa Sarai
+E: cyphar@cyphar.com
+W: https://www.cyphar.com/
+D: `pids` cgroup subsystem
+
N: Dipankar Sarma
E: dipankar@in.ibm.com
D: RCU
diff --git a/Documentation/cgroups/00-INDEX b/Documentation/cgroups/00-INDEX
index 96ce071..3f5a40f 100644
--- a/Documentation/cgroups/00-INDEX
+++ b/Documentation/cgroups/00-INDEX
@@ -22,6 +22,8 @@
- Network classifier cgroups details and usages.
net_prio.txt
- Network priority cgroups details and usages.
+pids.txt
+ - Process number cgroups details and usages.
resource_counter.txt
- Resource Counter API.
unified-hierarchy.txt
diff --git a/Documentation/cgroups/pids.txt b/Documentation/cgroups/pids.txt
new file mode 100644
index 0000000..1a078b5
--- /dev/null
+++ b/Documentation/cgroups/pids.txt
@@ -0,0 +1,85 @@
+ Process Number Controller
+ =========================
+
+Abstract
+--------
+
+The process number controller is used to allow a cgroup hierarchy to stop any
+new tasks from being fork()'d or clone()'d after a certain limit is reached.
+
+Since it is trivial to hit the task limit without hitting any kmemcg limits in
+place, PIDs are a fundamental resource. As such, PID exhaustion must be
+preventable in the scope of a cgroup hierarchy by allowing resource limiting of
+the number of tasks in a cgroup.
+
+Usage
+-----
+
+In order to use the `pids` controller, set the maximum number of tasks in
+pids.max (this is not available in the root cgroup for obvious reasons). The
+number of processes currently in the cgroup is given by pids.current.
+
+Organisational operations are not blocked by cgroup policies, so it is possible
+to have pids.current > pids.max. This can be done by either setting the limit to
+be smaller than pids.current, or attaching enough processes to the cgroup such
+that pids.current > pids.max. However, it is not possible to violate a cgroup
+policy through fork() or clone(). fork() and clone() will return -EAGAIN if the
+creation of a new process would cause a cgroup policy to be violated.
+
+To set a cgroup to have no limit, set pids.max to "max". This is the default for
+all new cgroups (N.B. that PID limits are hierarchical, so the most stringent
+limit in the hierarchy is followed).
+
+pids.current tracks all child cgroup hierarchies, so parent/pids.current is a
+superset of parent/child/pids.current.
+
+Example
+-------
+
+First, we mount the pids controller:
+# mkdir -p /sys/fs/cgroup/pids
+# mount -t cgroup -o pids none /sys/fs/cgroup/pids
+
+Then we create a hierarchy, set limits and attach processes to it:
+# mkdir -p /sys/fs/cgroup/pids/parent/child
+# echo 2 > /sys/fs/cgroup/pids/parent/pids.max
+# echo $$ > /sys/fs/cgroup/pids/parent/cgroup.procs
+# cat /sys/fs/cgroup/pids/parent/pids.current
+2
+#
+
+It should be noted that attempts to overcome the set limit (2 in this case) will
+fail:
+
+# cat /sys/fs/cgroup/pids/parent/pids.current
+2
+# ( /bin/echo "Here's some processes for you." | cat )
+sh: fork: Resource temporary unavailable
+#
+
+Even if we migrate to a child cgroup (which doesn't have a set limit), we will
+not be able to overcome the most stringent limit in the hierarchy (in this case,
+parent's):
+
+# echo $$ > /sys/fs/cgroup/pids/parent/child/cgroup.procs
+# cat /sys/fs/cgroup/pids/parent/pids.current
+2
+# cat /sys/fs/cgroup/pids/parent/child/pids.current
+2
+# cat /sys/fs/cgroup/pids/parent/child/pids.max
+max
+# ( /bin/echo "Here's some processes for you." | cat )
+sh: fork: Resource temporary unavailable
+#
+
+We can set a limit that is smaller than pids.current, which will stop any new
+processes from being forked at all (note that the shell itself counts towards
+pids.current):
+
+# echo 1 > /sys/fs/cgroup/pids/parent/pids.max
+# /bin/echo "We can't even spawn a single process now."
+sh: fork: Resource temporary unavailable
+# echo 0 > /sys/fs/cgroup/pids/parent/pids.max
+# /bin/echo "We can't even spawn a single process now."
+sh: fork: Resource temporary unavailable
+#
diff --git a/Documentation/cgroups/unified-hierarchy.txt b/Documentation/cgroups/unified-hierarchy.txt
index 86847a7..1ee9caf 100644
--- a/Documentation/cgroups/unified-hierarchy.txt
+++ b/Documentation/cgroups/unified-hierarchy.txt
@@ -23,10 +23,13 @@
5. Other Changes
5-1. [Un]populated Notification
5-2. Other Core Changes
- 5-3. Per-Controller Changes
- 5-3-1. blkio
- 5-3-2. cpuset
- 5-3-3. memory
+ 5-3. Controller File Conventions
+ 5-3-1. Format
+ 5-3-2. Control Knobs
+ 5-4. Per-Controller Changes
+ 5-4-1. blkio
+ 5-4-2. cpuset
+ 5-4-3. memory
6. Planned Changes
6-1. CAP for resource control
@@ -372,14 +375,75 @@
- The "cgroup.clone_children" file is removed.
-5-3. Per-Controller Changes
+5-3. Controller File Conventions
-5-3-1. blkio
+5-3-1. Format
+
+In general, all controller files should be in one of the following
+formats whenever possible.
+
+- Values only files
+
+ VAL0 VAL1...\n
+
+- Flat keyed files
+
+ KEY0 VAL0\n
+ KEY1 VAL1\n
+ ...
+
+- Nested keyed files
+
+ KEY0 SUB_KEY0=VAL00 SUB_KEY1=VAL01...
+ KEY1 SUB_KEY0=VAL10 SUB_KEY1=VAL11...
+ ...
+
+For a writeable file, the format for writing should generally match
+reading; however, controllers may allow omitting later fields or
+implement restricted shortcuts for most common use cases.
+
+For both flat and nested keyed files, only the values for a single key
+can be written at a time. For nested keyed files, the sub key pairs
+may be specified in any order and not all pairs have to be specified.
+
+
+5-3-2. Control Knobs
+
+- Settings for a single feature should generally be implemented in a
+ single file.
+
+- In general, the root cgroup should be exempt from resource control
+ and thus shouldn't have resource control knobs.
+
+- If a controller implements ratio based resource distribution, the
+ control knob should be named "weight" and have the range [1, 10000]
+ and 100 should be the default value. The values are chosen to allow
+ enough and symmetric bias in both directions while keeping it
+ intuitive (the default is 100%).
+
+- If a controller implements an absolute resource guarantee and/or
+ limit, the control knobs should be named "min" and "max"
+ respectively. If a controller implements best effort resource
+ gurantee and/or limit, the control knobs should be named "low" and
+ "high" respectively.
+
+ In the above four control files, the special token "max" should be
+ used to represent upward infinity for both reading and writing.
+
+- If a setting has configurable default value and specific overrides,
+ the default settings should be keyed with "default" and appear as
+ the first entry in the file. Specific entries can use "default" as
+ its value to indicate inheritance of the default value.
+
+
+5-4. Per-Controller Changes
+
+5-4-1. blkio
- blk-throttle becomes properly hierarchical.
-5-3-2. cpuset
+5-4-2. cpuset
- Tasks are kept in empty cpusets after hotplug and take on the masks
of the nearest non-empty ancestor, instead of being moved to it.
@@ -388,7 +452,7 @@
masks of the nearest non-empty ancestor.
-5-3-3. memory
+5-4-3. memory
- use_hierarchy is on by default and the cgroup file for the flag is
not created.
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 93755a6..4d8fcf2 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -34,12 +34,17 @@
/* define the enumeration of all cgroup subsystems */
#define SUBSYS(_x) _x ## _cgrp_id,
+#define SUBSYS_TAG(_t) CGROUP_ ## _t, \
+ __unused_tag_ ## _t = CGROUP_ ## _t - 1,
enum cgroup_subsys_id {
#include <linux/cgroup_subsys.h>
CGROUP_SUBSYS_COUNT,
};
+#undef SUBSYS_TAG
#undef SUBSYS
+#define CGROUP_CANFORK_COUNT (CGROUP_CANFORK_END - CGROUP_CANFORK_START)
+
/* bits in struct cgroup_subsys_state flags field */
enum {
CSS_NO_REF = (1 << 0), /* no reference counting for this css */
@@ -318,7 +323,7 @@
* end of cftype array.
*/
char name[MAX_CFTYPE_NAME];
- int private;
+ unsigned long private;
/*
* If not 0, file mode is set to this value, otherwise it will
* be figured out automatically
@@ -406,7 +411,9 @@
struct cgroup_taskset *tset);
void (*attach)(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset);
- void (*fork)(struct task_struct *task);
+ int (*can_fork)(struct task_struct *task, void **priv_p);
+ void (*cancel_fork)(struct task_struct *task, void *priv);
+ void (*fork)(struct task_struct *task, void *priv);
void (*exit)(struct cgroup_subsys_state *css,
struct cgroup_subsys_state *old_css,
struct task_struct *task);
@@ -434,6 +441,9 @@
int id;
const char *name;
+ /* optional, initialized automatically during boot if not set */
+ const char *legacy_name;
+
/* link to parent, protected by cgroup_lock() */
struct cgroup_root *root;
@@ -491,6 +501,7 @@
#else /* CONFIG_CGROUPS */
+#define CGROUP_CANFORK_COUNT 0
#define CGROUP_SUBSYS_COUNT 0
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk) {}
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a593e29..eb7ca55 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -22,6 +22,15 @@
#ifdef CONFIG_CGROUPS
+/*
+ * All weight knobs on the default hierarhcy should use the following min,
+ * default and max values. The default value is the logarithmic center of
+ * MIN and MAX and allows 100x to be expressed in both directions.
+ */
+#define CGROUP_WEIGHT_MIN 1
+#define CGROUP_WEIGHT_DFL 100
+#define CGROUP_WEIGHT_MAX 10000
+
/* a css_task_iter should be treated as an opaque object */
struct css_task_iter {
struct cgroup_subsys *ss;
@@ -62,7 +71,12 @@
struct pid *pid, struct task_struct *tsk);
void cgroup_fork(struct task_struct *p);
-void cgroup_post_fork(struct task_struct *p);
+extern int cgroup_can_fork(struct task_struct *p,
+ void *ss_priv[CGROUP_CANFORK_COUNT]);
+extern void cgroup_cancel_fork(struct task_struct *p,
+ void *ss_priv[CGROUP_CANFORK_COUNT]);
+extern void cgroup_post_fork(struct task_struct *p,
+ void *old_ss_priv[CGROUP_CANFORK_COUNT]);
void cgroup_exit(struct task_struct *p);
int cgroup_init_early(void);
@@ -524,7 +538,13 @@
struct dentry *dentry) { return -EINVAL; }
static inline void cgroup_fork(struct task_struct *p) {}
-static inline void cgroup_post_fork(struct task_struct *p) {}
+static inline int cgroup_can_fork(struct task_struct *p,
+ void *ss_priv[CGROUP_CANFORK_COUNT])
+{ return 0; }
+static inline void cgroup_cancel_fork(struct task_struct *p,
+ void *ss_priv[CGROUP_CANFORK_COUNT]) {}
+static inline void cgroup_post_fork(struct task_struct *p,
+ void *ss_priv[CGROUP_CANFORK_COUNT]) {}
static inline void cgroup_exit(struct task_struct *p) {}
static inline int cgroup_init_early(void) { return 0; }
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index e4a96fb..1f36945 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -3,6 +3,17 @@
*
* DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
*/
+
+/*
+ * This file *must* be included with SUBSYS() defined.
+ * SUBSYS_TAG() is a noop if undefined.
+ */
+
+#ifndef SUBSYS_TAG
+#define __TMP_SUBSYS_TAG
+#define SUBSYS_TAG(_x)
+#endif
+
#if IS_ENABLED(CONFIG_CPUSETS)
SUBSYS(cpuset)
#endif
@@ -48,11 +59,28 @@
#endif
/*
+ * Subsystems that implement the can_fork() family of callbacks.
+ */
+SUBSYS_TAG(CANFORK_START)
+
+#if IS_ENABLED(CONFIG_CGROUP_PIDS)
+SUBSYS(pids)
+#endif
+
+SUBSYS_TAG(CANFORK_END)
+
+/*
* The following subsystems are not supported on the default hierarchy.
*/
#if IS_ENABLED(CONFIG_CGROUP_DEBUG)
SUBSYS(debug)
#endif
+
+#ifdef __TMP_SUBSYS_TAG
+#undef __TMP_SUBSYS_TAG
+#undef SUBSYS_TAG
+#endif
+
/*
* DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
*/
diff --git a/init/Kconfig b/init/Kconfig
index ba1e6ea..bb9b4dd 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -947,6 +947,22 @@
Provides a way to freeze and unfreeze all tasks in a
cgroup.
+config CGROUP_PIDS
+ bool "PIDs cgroup subsystem"
+ help
+ Provides enforcement of process number limits in the scope of a
+ cgroup. Any attempt to fork more processes than is allowed in the
+ cgroup will fail. PIDs are fundamentally a global resource because it
+ is fairly trivial to reach PID exhaustion before you reach even a
+ conservative kmemcg limit. As a result, it is possible to grind a
+ system to halt without being limited by other cgroup policies. The
+ PIDs cgroup subsystem is designed to stop this from happening.
+
+ It should be noted that organisational operations (such as attaching
+ to a cgroup hierarchy will *not* be blocked by the PIDs subsystem),
+ since the PIDs limit only affects a process's ability to fork, not to
+ attach to a cgroup.
+
config CGROUP_DEVICE
bool "Device controller for cgroups"
help
diff --git a/kernel/Makefile b/kernel/Makefile
index 43c4c92..718fb8a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -55,6 +55,7 @@
obj-$(CONFIG_COMPAT) += compat.o
obj-$(CONFIG_CGROUPS) += cgroup.o
obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
+obj-$(CONFIG_CGROUP_PIDS) += cgroup_pids.o
obj-$(CONFIG_CPUSETS) += cpuset.o
obj-$(CONFIG_UTS_NS) += utsname.o
obj-$(CONFIG_USER_NS) += user_namespace.o
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b89f316..f3f5cd5e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -145,6 +145,7 @@
* part of that cgroup.
*/
struct cgroup_root cgrp_dfl_root;
+EXPORT_SYMBOL_GPL(cgrp_dfl_root);
/*
* The default hierarchy always exists but is hidden until mounted for the
@@ -186,6 +187,9 @@
static unsigned long have_fork_callback __read_mostly;
static unsigned long have_exit_callback __read_mostly;
+/* Ditto for the can_fork callback. */
+static unsigned long have_canfork_callback __read_mostly;
+
static struct cftype cgroup_dfl_base_files[];
static struct cftype cgroup_legacy_base_files[];
@@ -207,7 +211,7 @@
idr_preload(gfp_mask);
spin_lock_bh(&cgroup_idr_lock);
- ret = idr_alloc(idr, ptr, start, end, gfp_mask);
+ ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_WAIT);
spin_unlock_bh(&cgroup_idr_lock);
idr_preload_end();
return ret;
@@ -1027,10 +1031,13 @@
static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
char *buf)
{
+ struct cgroup_subsys *ss = cft->ss;
+
if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
!(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
- cft->ss->name, cft->name);
+ cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
+ cft->name);
else
strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
return buf;
@@ -1332,9 +1339,10 @@
struct cgroup_subsys *ss;
int ssid;
- for_each_subsys(ss, ssid)
- if (root->subsys_mask & (1 << ssid))
- seq_printf(seq, ",%s", ss->name);
+ if (root != &cgrp_dfl_root)
+ for_each_subsys(ss, ssid)
+ if (root->subsys_mask & (1 << ssid))
+ seq_printf(seq, ",%s", ss->legacy_name);
if (root->flags & CGRP_ROOT_NOPREFIX)
seq_puts(seq, ",noprefix");
if (root->flags & CGRP_ROOT_XATTR)
@@ -1447,7 +1455,7 @@
}
for_each_subsys(ss, i) {
- if (strcmp(token, ss->name))
+ if (strcmp(token, ss->legacy_name))
continue;
if (ss->disabled)
continue;
@@ -1666,7 +1674,7 @@
lockdep_assert_held(&cgroup_mutex);
- ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_NOWAIT);
+ ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
if (ret < 0)
goto out;
root_cgrp->id = ret;
@@ -4579,7 +4587,7 @@
if (err)
goto err_free_css;
- err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_NOWAIT);
+ err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
if (err < 0)
goto err_free_percpu_ref;
css->id = err;
@@ -4656,7 +4664,7 @@
* Temporarily set the pointer to NULL, so idr_find() won't return
* a half-baked cgroup.
*/
- cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_NOWAIT);
+ cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
if (cgrp->id < 0) {
ret = -ENOMEM;
goto out_cancel_ref;
@@ -4955,6 +4963,7 @@
have_fork_callback |= (bool)ss->fork << ss->id;
have_exit_callback |= (bool)ss->exit << ss->id;
+ have_canfork_callback |= (bool)ss->can_fork << ss->id;
/* At system boot, before all subsystems have been
* registered, no tasks have been forked, so we don't
@@ -4993,6 +5002,8 @@
ss->id = i;
ss->name = cgroup_subsys_name[i];
+ if (!ss->legacy_name)
+ ss->legacy_name = cgroup_subsys_name[i];
if (ss->early_init)
cgroup_init_subsys(ss, true);
@@ -5136,9 +5147,11 @@
continue;
seq_printf(m, "%d:", root->hierarchy_id);
- for_each_subsys(ss, ssid)
- if (root->subsys_mask & (1 << ssid))
- seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+ if (root != &cgrp_dfl_root)
+ for_each_subsys(ss, ssid)
+ if (root->subsys_mask & (1 << ssid))
+ seq_printf(m, "%s%s", count++ ? "," : "",
+ ss->legacy_name);
if (strlen(root->name))
seq_printf(m, "%sname=%s", count ? "," : "",
root->name);
@@ -5178,7 +5191,7 @@
for_each_subsys(ss, i)
seq_printf(m, "%s\t%d\t%d\t%d\n",
- ss->name, ss->root->hierarchy_id,
+ ss->legacy_name, ss->root->hierarchy_id,
atomic_read(&ss->root->nr_cgrps), !ss->disabled);
mutex_unlock(&cgroup_mutex);
@@ -5197,6 +5210,19 @@
.release = single_release,
};
+static void **subsys_canfork_priv_p(void *ss_priv[CGROUP_CANFORK_COUNT], int i)
+{
+ if (CGROUP_CANFORK_START <= i && i < CGROUP_CANFORK_END)
+ return &ss_priv[i - CGROUP_CANFORK_START];
+ return NULL;
+}
+
+static void *subsys_canfork_priv(void *ss_priv[CGROUP_CANFORK_COUNT], int i)
+{
+ void **private = subsys_canfork_priv_p(ss_priv, i);
+ return private ? *private : NULL;
+}
+
/**
* cgroup_fork - initialize cgroup related fields during copy_process()
* @child: pointer to task_struct of forking parent process.
@@ -5212,6 +5238,57 @@
}
/**
+ * cgroup_can_fork - called on a new task before the process is exposed
+ * @child: the task in question.
+ *
+ * This calls the subsystem can_fork() callbacks. If the can_fork() callback
+ * returns an error, the fork aborts with that error code. This allows for
+ * a cgroup subsystem to conditionally allow or deny new forks.
+ */
+int cgroup_can_fork(struct task_struct *child,
+ void *ss_priv[CGROUP_CANFORK_COUNT])
+{
+ struct cgroup_subsys *ss;
+ int i, j, ret;
+
+ for_each_subsys_which(ss, i, &have_canfork_callback) {
+ ret = ss->can_fork(child, subsys_canfork_priv_p(ss_priv, i));
+ if (ret)
+ goto out_revert;
+ }
+
+ return 0;
+
+out_revert:
+ for_each_subsys(ss, j) {
+ if (j >= i)
+ break;
+ if (ss->cancel_fork)
+ ss->cancel_fork(child, subsys_canfork_priv(ss_priv, j));
+ }
+
+ return ret;
+}
+
+/**
+ * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
+ * @child: the task in question
+ *
+ * This calls the cancel_fork() callbacks if a fork failed *after*
+ * cgroup_can_fork() succeded.
+ */
+void cgroup_cancel_fork(struct task_struct *child,
+ void *ss_priv[CGROUP_CANFORK_COUNT])
+{
+ struct cgroup_subsys *ss;
+ int i;
+
+ for_each_subsys(ss, i)
+ if (ss->cancel_fork)
+ ss->cancel_fork(child, subsys_canfork_priv(ss_priv, i));
+}
+
+/**
* cgroup_post_fork - called on a new task after adding it to the task list
* @child: the task in question
*
@@ -5221,7 +5298,8 @@
* cgroup_task_iter_start() - to guarantee that the new task ends up on its
* list.
*/
-void cgroup_post_fork(struct task_struct *child)
+void cgroup_post_fork(struct task_struct *child,
+ void *old_ss_priv[CGROUP_CANFORK_COUNT])
{
struct cgroup_subsys *ss;
int i;
@@ -5266,7 +5344,7 @@
* and addition to css_set.
*/
for_each_subsys_which(ss, i, &have_fork_callback)
- ss->fork(child);
+ ss->fork(child, subsys_canfork_priv(old_ss_priv, i));
}
/**
@@ -5400,12 +5478,14 @@
continue;
for_each_subsys(ss, i) {
- if (!strcmp(token, ss->name)) {
- ss->disabled = 1;
- printk(KERN_INFO "Disabling %s control group"
- " subsystem\n", ss->name);
- break;
- }
+ if (strcmp(token, ss->name) &&
+ strcmp(token, ss->legacy_name))
+ continue;
+
+ ss->disabled = 1;
+ printk(KERN_INFO "Disabling %s control group subsystem\n",
+ ss->name);
+ break;
}
}
return 1;
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 92b98cc..f1b30ad 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -203,7 +203,7 @@
* to do anything as freezer_attach() will put @task into the appropriate
* state.
*/
-static void freezer_fork(struct task_struct *task)
+static void freezer_fork(struct task_struct *task, void *private)
{
struct freezer *freezer;
diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c
new file mode 100644
index 0000000..806cd76
--- /dev/null
+++ b/kernel/cgroup_pids.c
@@ -0,0 +1,355 @@
+/*
+ * Process number limiting controller for cgroups.
+ *
+ * Used to allow a cgroup hierarchy to stop any new processes from fork()ing
+ * after a certain limit is reached.
+ *
+ * Since it is trivial to hit the task limit without hitting any kmemcg limits
+ * in place, PIDs are a fundamental resource. As such, PID exhaustion must be
+ * preventable in the scope of a cgroup hierarchy by allowing resource limiting
+ * of the number of tasks in a cgroup.
+ *
+ * In order to use the `pids` controller, set the maximum number of tasks in
+ * pids.max (this is not available in the root cgroup for obvious reasons). The
+ * number of processes currently in the cgroup is given by pids.current.
+ * Organisational operations are not blocked by cgroup policies, so it is
+ * possible to have pids.current > pids.max. However, it is not possible to
+ * violate a cgroup policy through fork(). fork() will return -EAGAIN if forking
+ * would cause a cgroup policy to be violated.
+ *
+ * To set a cgroup to have no limit, set pids.max to "max". This is the default
+ * for all new cgroups (N.B. that PID limits are hierarchical, so the most
+ * stringent limit in the hierarchy is followed).
+ *
+ * pids.current tracks all child cgroup hierarchies, so parent/pids.current is
+ * a superset of parent/child/pids.current.
+ *
+ * Copyright (C) 2015 Aleksa Sarai <cyphar@cyphar.com>
+ *
+ * This file is subject to the terms and conditions of version 2 of the GNU
+ * General Public License. See the file COPYING in the main directory of the
+ * Linux distribution for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/threads.h>
+#include <linux/atomic.h>
+#include <linux/cgroup.h>
+#include <linux/slab.h>
+
+#define PIDS_MAX (PID_MAX_LIMIT + 1ULL)
+#define PIDS_MAX_STR "max"
+
+struct pids_cgroup {
+ struct cgroup_subsys_state css;
+
+ /*
+ * Use 64-bit types so that we can safely represent "max" as
+ * %PIDS_MAX = (%PID_MAX_LIMIT + 1).
+ */
+ atomic64_t counter;
+ int64_t limit;
+};
+
+static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css)
+{
+ return container_of(css, struct pids_cgroup, css);
+}
+
+static struct pids_cgroup *parent_pids(struct pids_cgroup *pids)
+{
+ return css_pids(pids->css.parent);
+}
+
+static struct cgroup_subsys_state *
+pids_css_alloc(struct cgroup_subsys_state *parent)
+{
+ struct pids_cgroup *pids;
+
+ pids = kzalloc(sizeof(struct pids_cgroup), GFP_KERNEL);
+ if (!pids)
+ return ERR_PTR(-ENOMEM);
+
+ pids->limit = PIDS_MAX;
+ atomic64_set(&pids->counter, 0);
+ return &pids->css;
+}
+
+static void pids_css_free(struct cgroup_subsys_state *css)
+{
+ kfree(css_pids(css));
+}
+
+/**
+ * pids_cancel - uncharge the local pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to cancel
+ *
+ * This function will WARN if the pid count goes under 0, because such a case is
+ * a bug in the pids controller proper.
+ */
+static void pids_cancel(struct pids_cgroup *pids, int num)
+{
+ /*
+ * A negative count (or overflow for that matter) is invalid,
+ * and indicates a bug in the `pids` controller proper.
+ */
+ WARN_ON_ONCE(atomic64_add_negative(-num, &pids->counter));
+}
+
+/**
+ * pids_uncharge - hierarchically uncharge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to uncharge
+ */
+static void pids_uncharge(struct pids_cgroup *pids, int num)
+{
+ struct pids_cgroup *p;
+
+ for (p = pids; p; p = parent_pids(p))
+ pids_cancel(p, num);
+}
+
+/**
+ * pids_charge - hierarchically charge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to charge
+ *
+ * This function does *not* follow the pid limit set. It cannot fail and the new
+ * pid count may exceed the limit. This is only used for reverting failed
+ * attaches, where there is no other way out than violating the limit.
+ */
+static void pids_charge(struct pids_cgroup *pids, int num)
+{
+ struct pids_cgroup *p;
+
+ for (p = pids; p; p = parent_pids(p))
+ atomic64_add(num, &p->counter);
+}
+
+/**
+ * pids_try_charge - hierarchically try to charge the pid count
+ * @pids: the pid cgroup state
+ * @num: the number of pids to charge
+ *
+ * This function follows the set limit. It will fail if the charge would cause
+ * the new value to exceed the hierarchical limit. Returns 0 if the charge
+ * succeded, otherwise -EAGAIN.
+ */
+static int pids_try_charge(struct pids_cgroup *pids, int num)
+{
+ struct pids_cgroup *p, *q;
+
+ for (p = pids; p; p = parent_pids(p)) {
+ int64_t new = atomic64_add_return(num, &p->counter);
+
+ /*
+ * Since new is capped to the maximum number of pid_t, if
+ * p->limit is %PIDS_MAX then we know that this test will never
+ * fail.
+ */
+ if (new > p->limit)
+ goto revert;
+ }
+
+ return 0;
+
+revert:
+ for (q = pids; q != p; q = parent_pids(q))
+ pids_cancel(q, num);
+ pids_cancel(p, num);
+
+ return -EAGAIN;
+}
+
+static int pids_can_attach(struct cgroup_subsys_state *css,
+ struct cgroup_taskset *tset)
+{
+ struct pids_cgroup *pids = css_pids(css);
+ struct task_struct *task;
+
+ cgroup_taskset_for_each(task, tset) {
+ struct cgroup_subsys_state *old_css;
+ struct pids_cgroup *old_pids;
+
+ /*
+ * No need to pin @old_css between here and cancel_attach()
+ * because cgroup core protects it from being freed before
+ * the migration completes or fails.
+ */
+ old_css = task_css(task, pids_cgrp_id);
+ old_pids = css_pids(old_css);
+
+ pids_charge(pids, 1);
+ pids_uncharge(old_pids, 1);
+ }
+
+ return 0;
+}
+
+static void pids_cancel_attach(struct cgroup_subsys_state *css,
+ struct cgroup_taskset *tset)
+{
+ struct pids_cgroup *pids = css_pids(css);
+ struct task_struct *task;
+
+ cgroup_taskset_for_each(task, tset) {
+ struct cgroup_subsys_state *old_css;
+ struct pids_cgroup *old_pids;
+
+ old_css = task_css(task, pids_cgrp_id);
+ old_pids = css_pids(old_css);
+
+ pids_charge(old_pids, 1);
+ pids_uncharge(pids, 1);
+ }
+}
+
+static int pids_can_fork(struct task_struct *task, void **priv_p)
+{
+ struct cgroup_subsys_state *css;
+ struct pids_cgroup *pids;
+ int err;
+
+ /*
+ * Use the "current" task_css for the pids subsystem as the tentative
+ * css. It is possible we will charge the wrong hierarchy, in which
+ * case we will forcefully revert/reapply the charge on the right
+ * hierarchy after it is committed to the task proper.
+ */
+ css = task_get_css(current, pids_cgrp_id);
+ pids = css_pids(css);
+
+ err = pids_try_charge(pids, 1);
+ if (err)
+ goto err_css_put;
+
+ *priv_p = css;
+ return 0;
+
+err_css_put:
+ css_put(css);
+ return err;
+}
+
+static void pids_cancel_fork(struct task_struct *task, void *priv)
+{
+ struct cgroup_subsys_state *css = priv;
+ struct pids_cgroup *pids = css_pids(css);
+
+ pids_uncharge(pids, 1);
+ css_put(css);
+}
+
+static void pids_fork(struct task_struct *task, void *priv)
+{
+ struct cgroup_subsys_state *css;
+ struct cgroup_subsys_state *old_css = priv;
+ struct pids_cgroup *pids;
+ struct pids_cgroup *old_pids = css_pids(old_css);
+
+ css = task_get_css(task, pids_cgrp_id);
+ pids = css_pids(css);
+
+ /*
+ * If the association has changed, we have to revert and reapply the
+ * charge/uncharge on the wrong hierarchy to the current one. Since
+ * the association can only change due to an organisation event, its
+ * okay for us to ignore the limit in this case.
+ */
+ if (pids != old_pids) {
+ pids_uncharge(old_pids, 1);
+ pids_charge(pids, 1);
+ }
+
+ css_put(css);
+ css_put(old_css);
+}
+
+static void pids_exit(struct cgroup_subsys_state *css,
+ struct cgroup_subsys_state *old_css,
+ struct task_struct *task)
+{
+ struct pids_cgroup *pids = css_pids(old_css);
+
+ pids_uncharge(pids, 1);
+}
+
+static ssize_t pids_max_write(struct kernfs_open_file *of, char *buf,
+ size_t nbytes, loff_t off)
+{
+ struct cgroup_subsys_state *css = of_css(of);
+ struct pids_cgroup *pids = css_pids(css);
+ int64_t limit;
+ int err;
+
+ buf = strstrip(buf);
+ if (!strcmp(buf, PIDS_MAX_STR)) {
+ limit = PIDS_MAX;
+ goto set_limit;
+ }
+
+ err = kstrtoll(buf, 0, &limit);
+ if (err)
+ return err;
+
+ if (limit < 0 || limit >= PIDS_MAX)
+ return -EINVAL;
+
+set_limit:
+ /*
+ * Limit updates don't need to be mutex'd, since it isn't
+ * critical that any racing fork()s follow the new limit.
+ */
+ pids->limit = limit;
+ return nbytes;
+}
+
+static int pids_max_show(struct seq_file *sf, void *v)
+{
+ struct cgroup_subsys_state *css = seq_css(sf);
+ struct pids_cgroup *pids = css_pids(css);
+ int64_t limit = pids->limit;
+
+ if (limit >= PIDS_MAX)
+ seq_printf(sf, "%s\n", PIDS_MAX_STR);
+ else
+ seq_printf(sf, "%lld\n", limit);
+
+ return 0;
+}
+
+static s64 pids_current_read(struct cgroup_subsys_state *css,
+ struct cftype *cft)
+{
+ struct pids_cgroup *pids = css_pids(css);
+
+ return atomic64_read(&pids->counter);
+}
+
+static struct cftype pids_files[] = {
+ {
+ .name = "max",
+ .write = pids_max_write,
+ .seq_show = pids_max_show,
+ .flags = CFTYPE_NOT_ON_ROOT,
+ },
+ {
+ .name = "current",
+ .read_s64 = pids_current_read,
+ },
+ { } /* terminate */
+};
+
+struct cgroup_subsys pids_cgrp_subsys = {
+ .css_alloc = pids_css_alloc,
+ .css_free = pids_css_free,
+ .can_attach = pids_can_attach,
+ .cancel_attach = pids_cancel_attach,
+ .can_fork = pids_can_fork,
+ .cancel_fork = pids_cancel_fork,
+ .fork = pids_fork,
+ .exit = pids_exit,
+ .legacy_cftypes = pids_files,
+ .dfl_cftypes = pids_files,
+};
diff --git a/kernel/fork.c b/kernel/fork.c
index 2b1a61c..03aa2e6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1246,6 +1246,7 @@
{
int retval;
struct task_struct *p;
+ void *cgrp_ss_priv[CGROUP_CANFORK_COUNT] = {};
if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
@@ -1518,6 +1519,16 @@
p->task_works = NULL;
/*
+ * Ensure that the cgroup subsystem policies allow the new process to be
+ * forked. It should be noted the the new process's css_set can be changed
+ * between here and cgroup_post_fork() if an organisation operation is in
+ * progress.
+ */
+ retval = cgroup_can_fork(p, cgrp_ss_priv);
+ if (retval)
+ goto bad_fork_free_pid;
+
+ /*
* Make it visible to the rest of the system, but dont wake it up yet.
* Need tasklist lock for parent etc handling!
*/
@@ -1553,7 +1564,7 @@
spin_unlock(¤t->sighand->siglock);
write_unlock_irq(&tasklist_lock);
retval = -ERESTARTNOINTR;
- goto bad_fork_free_pid;
+ goto bad_fork_cancel_cgroup;
}
if (likely(p->pid)) {
@@ -1595,7 +1606,7 @@
write_unlock_irq(&tasklist_lock);
proc_fork_connector(p);
- cgroup_post_fork(p);
+ cgroup_post_fork(p, cgrp_ss_priv);
if (clone_flags & CLONE_THREAD)
threadgroup_change_end(current);
perf_event_fork(p);
@@ -1605,6 +1616,8 @@
return p;
+bad_fork_cancel_cgroup:
+ cgroup_cancel_fork(p, cgrp_ss_priv);
bad_fork_free_pid:
if (pid != &init_struct_pid)
free_pid(pid);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8b864ec..d8420c2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8133,7 +8133,7 @@
sched_offline_group(tg);
}
-static void cpu_cgroup_fork(struct task_struct *task)
+static void cpu_cgroup_fork(struct task_struct *task, void *private)
{
sched_move_task(task);
}