![Christian Brauner](/assets/img/avatar_default.png)
Replace hlist_empty() with the new pid_has_task() helper which is more idiomatic, easier to grep for, and unifies how callers perform this check. Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Link: https://lore.kernel.org/r/20191017101832.5985-3-christian.brauner@ubuntu.com
541 lines
13 KiB
C
541 lines
13 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
|
|
/*
|
|
* Generic pidhash and scalable, time-bounded PID allocator
|
|
*
|
|
* (C) 2002-2003 Nadia Yvette Chambers, IBM
|
|
* (C) 2004 Nadia Yvette Chambers, Oracle
|
|
* (C) 2002-2004 Ingo Molnar, Red Hat
|
|
*
|
|
* pid-structures are backing objects for tasks sharing a given ID to chain
|
|
* against. There is very little to them aside from hashing them and
|
|
* parking tasks using given ID's on a list.
|
|
*
|
|
* The hash is always changed with the tasklist_lock write-acquired,
|
|
* and the hash is only accessed with the tasklist_lock at least
|
|
* read-acquired, so there's no additional SMP locking needed here.
|
|
*
|
|
* We have a list of bitmap pages, which bitmaps represent the PID space.
|
|
* Allocating and freeing PIDs is completely lockless. The worst-case
|
|
* allocation scenario when all but one out of 1 million PIDs possible are
|
|
* allocated already: the scanning of 32 list entries and at most PAGE_SIZE
|
|
* bytes. The typical fastpath is a single successful setbit. Freeing is O(1).
|
|
*
|
|
* Pid namespaces:
|
|
* (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
|
|
* (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
|
|
* Many thanks to Oleg Nesterov for comments and help
|
|
*
|
|
*/
|
|
|
|
#include <linux/mm.h>
|
|
#include <linux/export.h>
|
|
#include <linux/slab.h>
|
|
#include <linux/init.h>
|
|
#include <linux/rculist.h>
|
|
#include <linux/memblock.h>
|
|
#include <linux/pid_namespace.h>
|
|
#include <linux/init_task.h>
|
|
#include <linux/syscalls.h>
|
|
#include <linux/proc_ns.h>
|
|
#include <linux/refcount.h>
|
|
#include <linux/anon_inodes.h>
|
|
#include <linux/sched/signal.h>
|
|
#include <linux/sched/task.h>
|
|
#include <linux/idr.h>
|
|
|
|
struct pid init_struct_pid = {
|
|
.count = REFCOUNT_INIT(1),
|
|
.tasks = {
|
|
{ .first = NULL },
|
|
{ .first = NULL },
|
|
{ .first = NULL },
|
|
},
|
|
.level = 0,
|
|
.numbers = { {
|
|
.nr = 0,
|
|
.ns = &init_pid_ns,
|
|
}, }
|
|
};
|
|
|
|
int pid_max = PID_MAX_DEFAULT;
|
|
|
|
#define RESERVED_PIDS 300
|
|
|
|
int pid_max_min = RESERVED_PIDS + 1;
|
|
int pid_max_max = PID_MAX_LIMIT;
|
|
|
|
/*
|
|
* PID-map pages start out as NULL, they get allocated upon
|
|
* first use and are never deallocated. This way a low pid_max
|
|
* value does not cause lots of bitmaps to be allocated, but
|
|
* the scheme scales to up to 4 million PIDs, runtime.
|
|
*/
|
|
struct pid_namespace init_pid_ns = {
|
|
.kref = KREF_INIT(2),
|
|
.idr = IDR_INIT(init_pid_ns.idr),
|
|
.pid_allocated = PIDNS_ADDING,
|
|
.level = 0,
|
|
.child_reaper = &init_task,
|
|
.user_ns = &init_user_ns,
|
|
.ns.inum = PROC_PID_INIT_INO,
|
|
#ifdef CONFIG_PID_NS
|
|
.ns.ops = &pidns_operations,
|
|
#endif
|
|
};
|
|
EXPORT_SYMBOL_GPL(init_pid_ns);
|
|
|
|
/*
|
|
* Note: disable interrupts while the pidmap_lock is held as an
|
|
* interrupt might come in and do read_lock(&tasklist_lock).
|
|
*
|
|
* If we don't disable interrupts there is a nasty deadlock between
|
|
* detach_pid()->free_pid() and another cpu that does
|
|
* spin_lock(&pidmap_lock) followed by an interrupt routine that does
|
|
* read_lock(&tasklist_lock);
|
|
*
|
|
* After we clean up the tasklist_lock and know there are no
|
|
* irq handlers that take it we can leave the interrupts enabled.
|
|
* For now it is easier to be safe than to prove it can't happen.
|
|
*/
|
|
|
|
static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
|
|
|
|
void put_pid(struct pid *pid)
|
|
{
|
|
struct pid_namespace *ns;
|
|
|
|
if (!pid)
|
|
return;
|
|
|
|
ns = pid->numbers[pid->level].ns;
|
|
if (refcount_dec_and_test(&pid->count)) {
|
|
kmem_cache_free(ns->pid_cachep, pid);
|
|
put_pid_ns(ns);
|
|
}
|
|
}
|
|
EXPORT_SYMBOL_GPL(put_pid);
|
|
|
|
static void delayed_put_pid(struct rcu_head *rhp)
|
|
{
|
|
struct pid *pid = container_of(rhp, struct pid, rcu);
|
|
put_pid(pid);
|
|
}
|
|
|
|
void free_pid(struct pid *pid)
|
|
{
|
|
/* We can be called with write_lock_irq(&tasklist_lock) held */
|
|
int i;
|
|
unsigned long flags;
|
|
|
|
spin_lock_irqsave(&pidmap_lock, flags);
|
|
for (i = 0; i <= pid->level; i++) {
|
|
struct upid *upid = pid->numbers + i;
|
|
struct pid_namespace *ns = upid->ns;
|
|
switch (--ns->pid_allocated) {
|
|
case 2:
|
|
case 1:
|
|
/* When all that is left in the pid namespace
|
|
* is the reaper wake up the reaper. The reaper
|
|
* may be sleeping in zap_pid_ns_processes().
|
|
*/
|
|
wake_up_process(ns->child_reaper);
|
|
break;
|
|
case PIDNS_ADDING:
|
|
/* Handle a fork failure of the first process */
|
|
WARN_ON(ns->child_reaper);
|
|
ns->pid_allocated = 0;
|
|
/* fall through */
|
|
case 0:
|
|
schedule_work(&ns->proc_work);
|
|
break;
|
|
}
|
|
|
|
idr_remove(&ns->idr, upid->nr);
|
|
}
|
|
spin_unlock_irqrestore(&pidmap_lock, flags);
|
|
|
|
call_rcu(&pid->rcu, delayed_put_pid);
|
|
}
|
|
|
|
struct pid *alloc_pid(struct pid_namespace *ns)
|
|
{
|
|
struct pid *pid;
|
|
enum pid_type type;
|
|
int i, nr;
|
|
struct pid_namespace *tmp;
|
|
struct upid *upid;
|
|
int retval = -ENOMEM;
|
|
|
|
pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
|
|
if (!pid)
|
|
return ERR_PTR(retval);
|
|
|
|
tmp = ns;
|
|
pid->level = ns->level;
|
|
|
|
for (i = ns->level; i >= 0; i--) {
|
|
int pid_min = 1;
|
|
|
|
idr_preload(GFP_KERNEL);
|
|
spin_lock_irq(&pidmap_lock);
|
|
|
|
/*
|
|
* init really needs pid 1, but after reaching the maximum
|
|
* wrap back to RESERVED_PIDS
|
|
*/
|
|
if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
|
|
pid_min = RESERVED_PIDS;
|
|
|
|
/*
|
|
* Store a null pointer so find_pid_ns does not find
|
|
* a partially initialized PID (see below).
|
|
*/
|
|
nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
|
|
pid_max, GFP_ATOMIC);
|
|
spin_unlock_irq(&pidmap_lock);
|
|
idr_preload_end();
|
|
|
|
if (nr < 0) {
|
|
retval = (nr == -ENOSPC) ? -EAGAIN : nr;
|
|
goto out_free;
|
|
}
|
|
|
|
pid->numbers[i].nr = nr;
|
|
pid->numbers[i].ns = tmp;
|
|
tmp = tmp->parent;
|
|
}
|
|
|
|
if (unlikely(is_child_reaper(pid))) {
|
|
if (pid_ns_prepare_proc(ns))
|
|
goto out_free;
|
|
}
|
|
|
|
get_pid_ns(ns);
|
|
refcount_set(&pid->count, 1);
|
|
for (type = 0; type < PIDTYPE_MAX; ++type)
|
|
INIT_HLIST_HEAD(&pid->tasks[type]);
|
|
|
|
init_waitqueue_head(&pid->wait_pidfd);
|
|
|
|
upid = pid->numbers + ns->level;
|
|
spin_lock_irq(&pidmap_lock);
|
|
if (!(ns->pid_allocated & PIDNS_ADDING))
|
|
goto out_unlock;
|
|
for ( ; upid >= pid->numbers; --upid) {
|
|
/* Make the PID visible to find_pid_ns. */
|
|
idr_replace(&upid->ns->idr, pid, upid->nr);
|
|
upid->ns->pid_allocated++;
|
|
}
|
|
spin_unlock_irq(&pidmap_lock);
|
|
|
|
return pid;
|
|
|
|
out_unlock:
|
|
spin_unlock_irq(&pidmap_lock);
|
|
put_pid_ns(ns);
|
|
|
|
out_free:
|
|
spin_lock_irq(&pidmap_lock);
|
|
while (++i <= ns->level) {
|
|
upid = pid->numbers + i;
|
|
idr_remove(&upid->ns->idr, upid->nr);
|
|
}
|
|
|
|
/* On failure to allocate the first pid, reset the state */
|
|
if (ns->pid_allocated == PIDNS_ADDING)
|
|
idr_set_cursor(&ns->idr, 0);
|
|
|
|
spin_unlock_irq(&pidmap_lock);
|
|
|
|
kmem_cache_free(ns->pid_cachep, pid);
|
|
return ERR_PTR(retval);
|
|
}
|
|
|
|
void disable_pid_allocation(struct pid_namespace *ns)
|
|
{
|
|
spin_lock_irq(&pidmap_lock);
|
|
ns->pid_allocated &= ~PIDNS_ADDING;
|
|
spin_unlock_irq(&pidmap_lock);
|
|
}
|
|
|
|
struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
|
|
{
|
|
return idr_find(&ns->idr, nr);
|
|
}
|
|
EXPORT_SYMBOL_GPL(find_pid_ns);
|
|
|
|
struct pid *find_vpid(int nr)
|
|
{
|
|
return find_pid_ns(nr, task_active_pid_ns(current));
|
|
}
|
|
EXPORT_SYMBOL_GPL(find_vpid);
|
|
|
|
static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
|
|
{
|
|
return (type == PIDTYPE_PID) ?
|
|
&task->thread_pid :
|
|
&task->signal->pids[type];
|
|
}
|
|
|
|
/*
|
|
* attach_pid() must be called with the tasklist_lock write-held.
|
|
*/
|
|
void attach_pid(struct task_struct *task, enum pid_type type)
|
|
{
|
|
struct pid *pid = *task_pid_ptr(task, type);
|
|
hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
|
|
}
|
|
|
|
static void __change_pid(struct task_struct *task, enum pid_type type,
|
|
struct pid *new)
|
|
{
|
|
struct pid **pid_ptr = task_pid_ptr(task, type);
|
|
struct pid *pid;
|
|
int tmp;
|
|
|
|
pid = *pid_ptr;
|
|
|
|
hlist_del_rcu(&task->pid_links[type]);
|
|
*pid_ptr = new;
|
|
|
|
for (tmp = PIDTYPE_MAX; --tmp >= 0; )
|
|
if (pid_has_task(pid, tmp))
|
|
return;
|
|
|
|
free_pid(pid);
|
|
}
|
|
|
|
void detach_pid(struct task_struct *task, enum pid_type type)
|
|
{
|
|
__change_pid(task, type, NULL);
|
|
}
|
|
|
|
void change_pid(struct task_struct *task, enum pid_type type,
|
|
struct pid *pid)
|
|
{
|
|
__change_pid(task, type, pid);
|
|
attach_pid(task, type);
|
|
}
|
|
|
|
/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
|
|
void transfer_pid(struct task_struct *old, struct task_struct *new,
|
|
enum pid_type type)
|
|
{
|
|
if (type == PIDTYPE_PID)
|
|
new->thread_pid = old->thread_pid;
|
|
hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
|
|
}
|
|
|
|
struct task_struct *pid_task(struct pid *pid, enum pid_type type)
|
|
{
|
|
struct task_struct *result = NULL;
|
|
if (pid) {
|
|
struct hlist_node *first;
|
|
first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
|
|
lockdep_tasklist_lock_is_held());
|
|
if (first)
|
|
result = hlist_entry(first, struct task_struct, pid_links[(type)]);
|
|
}
|
|
return result;
|
|
}
|
|
EXPORT_SYMBOL(pid_task);
|
|
|
|
/*
|
|
* Must be called under rcu_read_lock().
|
|
*/
|
|
struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
|
|
{
|
|
RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
|
|
"find_task_by_pid_ns() needs rcu_read_lock() protection");
|
|
return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
|
|
}
|
|
|
|
struct task_struct *find_task_by_vpid(pid_t vnr)
|
|
{
|
|
return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
|
|
}
|
|
|
|
struct task_struct *find_get_task_by_vpid(pid_t nr)
|
|
{
|
|
struct task_struct *task;
|
|
|
|
rcu_read_lock();
|
|
task = find_task_by_vpid(nr);
|
|
if (task)
|
|
get_task_struct(task);
|
|
rcu_read_unlock();
|
|
|
|
return task;
|
|
}
|
|
|
|
struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
|
|
{
|
|
struct pid *pid;
|
|
rcu_read_lock();
|
|
pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
|
|
rcu_read_unlock();
|
|
return pid;
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_task_pid);
|
|
|
|
struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
|
|
{
|
|
struct task_struct *result;
|
|
rcu_read_lock();
|
|
result = pid_task(pid, type);
|
|
if (result)
|
|
get_task_struct(result);
|
|
rcu_read_unlock();
|
|
return result;
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_pid_task);
|
|
|
|
struct pid *find_get_pid(pid_t nr)
|
|
{
|
|
struct pid *pid;
|
|
|
|
rcu_read_lock();
|
|
pid = get_pid(find_vpid(nr));
|
|
rcu_read_unlock();
|
|
|
|
return pid;
|
|
}
|
|
EXPORT_SYMBOL_GPL(find_get_pid);
|
|
|
|
pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
|
|
{
|
|
struct upid *upid;
|
|
pid_t nr = 0;
|
|
|
|
if (pid && ns->level <= pid->level) {
|
|
upid = &pid->numbers[ns->level];
|
|
if (upid->ns == ns)
|
|
nr = upid->nr;
|
|
}
|
|
return nr;
|
|
}
|
|
EXPORT_SYMBOL_GPL(pid_nr_ns);
|
|
|
|
pid_t pid_vnr(struct pid *pid)
|
|
{
|
|
return pid_nr_ns(pid, task_active_pid_ns(current));
|
|
}
|
|
EXPORT_SYMBOL_GPL(pid_vnr);
|
|
|
|
pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
|
|
struct pid_namespace *ns)
|
|
{
|
|
pid_t nr = 0;
|
|
|
|
rcu_read_lock();
|
|
if (!ns)
|
|
ns = task_active_pid_ns(current);
|
|
if (likely(pid_alive(task)))
|
|
nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
|
|
rcu_read_unlock();
|
|
|
|
return nr;
|
|
}
|
|
EXPORT_SYMBOL(__task_pid_nr_ns);
|
|
|
|
struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
|
|
{
|
|
return ns_of_pid(task_pid(tsk));
|
|
}
|
|
EXPORT_SYMBOL_GPL(task_active_pid_ns);
|
|
|
|
/*
|
|
* Used by proc to find the first pid that is greater than or equal to nr.
|
|
*
|
|
* If there is a pid at nr this function is exactly the same as find_pid_ns.
|
|
*/
|
|
struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
|
|
{
|
|
return idr_get_next(&ns->idr, &nr);
|
|
}
|
|
|
|
/**
|
|
* pidfd_create() - Create a new pid file descriptor.
|
|
*
|
|
* @pid: struct pid that the pidfd will reference
|
|
*
|
|
* This creates a new pid file descriptor with the O_CLOEXEC flag set.
|
|
*
|
|
* Note, that this function can only be called after the fd table has
|
|
* been unshared to avoid leaking the pidfd to the new process.
|
|
*
|
|
* Return: On success, a cloexec pidfd is returned.
|
|
* On error, a negative errno number will be returned.
|
|
*/
|
|
static int pidfd_create(struct pid *pid)
|
|
{
|
|
int fd;
|
|
|
|
fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
|
|
O_RDWR | O_CLOEXEC);
|
|
if (fd < 0)
|
|
put_pid(pid);
|
|
|
|
return fd;
|
|
}
|
|
|
|
/**
|
|
* pidfd_open() - Open new pid file descriptor.
|
|
*
|
|
* @pid: pid for which to retrieve a pidfd
|
|
* @flags: flags to pass
|
|
*
|
|
* This creates a new pid file descriptor with the O_CLOEXEC flag set for
|
|
* the process identified by @pid. Currently, the process identified by
|
|
* @pid must be a thread-group leader. This restriction currently exists
|
|
* for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot
|
|
* be used with CLONE_THREAD) and pidfd polling (only supports thread group
|
|
* leaders).
|
|
*
|
|
* Return: On success, a cloexec pidfd is returned.
|
|
* On error, a negative errno number will be returned.
|
|
*/
|
|
SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
|
|
{
|
|
int fd, ret;
|
|
struct pid *p;
|
|
|
|
if (flags)
|
|
return -EINVAL;
|
|
|
|
if (pid <= 0)
|
|
return -EINVAL;
|
|
|
|
p = find_get_pid(pid);
|
|
if (!p)
|
|
return -ESRCH;
|
|
|
|
ret = 0;
|
|
rcu_read_lock();
|
|
if (!pid_task(p, PIDTYPE_TGID))
|
|
ret = -EINVAL;
|
|
rcu_read_unlock();
|
|
|
|
fd = ret ?: pidfd_create(p);
|
|
put_pid(p);
|
|
return fd;
|
|
}
|
|
|
|
void __init pid_idr_init(void)
|
|
{
|
|
/* Verify no one has done anything silly: */
|
|
BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
|
|
|
|
/* bump default and minimum pid_max based on number of cpus */
|
|
pid_max = min(pid_max_max, max_t(int, pid_max,
|
|
PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
|
|
pid_max_min = max_t(int, pid_max_min,
|
|
PIDS_PER_CPU_MIN * num_possible_cpus());
|
|
pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
|
|
|
|
idr_init(&init_pid_ns.idr);
|
|
|
|
init_pid_ns.pid_cachep = KMEM_CACHE(pid,
|
|
SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
|
|
}
|