| // 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> |
| #include <net/sock.h> |
| #include <uapi/linux/pidfd.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; |
| 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, pid_t *set_tid, |
| size_t set_tid_size) |
| { |
| struct pid *pid; |
| enum pid_type type; |
| int i, nr; |
| struct pid_namespace *tmp; |
| struct upid *upid; |
| int retval = -ENOMEM; |
| |
| /* |
| * set_tid_size contains the size of the set_tid array. Starting at |
| * the most nested currently active PID namespace it tells alloc_pid() |
| * which PID to set for a process in that most nested PID namespace |
| * up to set_tid_size PID namespaces. It does not have to set the PID |
| * for a process in all nested PID namespaces but set_tid_size must |
| * never be greater than the current ns->level + 1. |
| */ |
| if (set_tid_size > ns->level + 1) |
| return ERR_PTR(-EINVAL); |
| |
| 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 tid = 0; |
| |
| if (set_tid_size) { |
| tid = set_tid[ns->level - i]; |
| |
| retval = -EINVAL; |
| if (tid < 1 || tid >= pid_max) |
| goto out_free; |
| /* |
| * Also fail if a PID != 1 is requested and |
| * no PID 1 exists. |
| */ |
| if (tid != 1 && !tmp->child_reaper) |
| goto out_free; |
| retval = -EPERM; |
| if (!checkpoint_restore_ns_capable(tmp->user_ns)) |
| goto out_free; |
| set_tid_size--; |
| } |
| |
| idr_preload(GFP_KERNEL); |
| spin_lock_irq(&pidmap_lock); |
| |
| if (tid) { |
| nr = idr_alloc(&tmp->idr, NULL, tid, |
| tid + 1, GFP_ATOMIC); |
| /* |
| * If ENOSPC is returned it means that the PID is |
| * alreay in use. Return EEXIST in that case. |
| */ |
| if (nr == -ENOSPC) |
| nr = -EEXIST; |
| } else { |
| int pid_min = 1; |
| /* |
| * 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; |
| } |
| |
| /* |
| * ENOMEM is not the most obvious choice especially for the case |
| * where the child subreaper has already exited and the pid |
| * namespace denies the creation of any new processes. But ENOMEM |
| * is what we have exposed to userspace for a long time and it is |
| * documented behavior for pid namespaces. So we can't easily |
| * change it even if there were an error code better suited. |
| */ |
| retval = -ENOMEM; |
| |
| get_pid_ns(ns); |
| refcount_set(&pid->count, 1); |
| spin_lock_init(&pid->lock); |
| for (type = 0; type < PIDTYPE_MAX; ++type) |
| INIT_HLIST_HEAD(&pid->tasks[type]); |
| |
| init_waitqueue_head(&pid->wait_pidfd); |
| INIT_HLIST_HEAD(&pid->inodes); |
| |
| 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); |
| } |
| |
| void exchange_tids(struct task_struct *left, struct task_struct *right) |
| { |
| struct pid *pid1 = left->thread_pid; |
| struct pid *pid2 = right->thread_pid; |
| struct hlist_head *head1 = &pid1->tasks[PIDTYPE_PID]; |
| struct hlist_head *head2 = &pid2->tasks[PIDTYPE_PID]; |
| |
| /* Swap the single entry tid lists */ |
| hlists_swap_heads_rcu(head1, head2); |
| |
| /* Swap the per task_struct pid */ |
| rcu_assign_pointer(left->thread_pid, pid2); |
| rcu_assign_pointer(right->thread_pid, pid1); |
| |
| /* Swap the cached value */ |
| WRITE_ONCE(left->pid, pid_nr(pid2)); |
| WRITE_ONCE(right->pid, pid_nr(pid1)); |
| } |
| |
| /* 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); |
| 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); |
| } |
| |
| struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags) |
| { |
| struct fd f; |
| struct pid *pid; |
| |
| f = fdget(fd); |
| if (!f.file) |
| return ERR_PTR(-EBADF); |
| |
| pid = pidfd_pid(f.file); |
| if (!IS_ERR(pid)) { |
| get_pid(pid); |
| *flags = f.file->f_flags; |
| } |
| |
| fdput(f); |
| return pid; |
| } |
| |
| /** |
| * pidfd_create() - Create a new pid file descriptor. |
| * |
| * @pid: struct pid that the pidfd will reference |
| * @flags: flags to pass |
| * |
| * 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, unsigned int flags) |
| { |
| int fd; |
| |
| fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid), |
| flags | 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; |
| struct pid *p; |
| |
| if (flags & ~PIDFD_NONBLOCK) |
| return -EINVAL; |
| |
| if (pid <= 0) |
| return -EINVAL; |
| |
| p = find_get_pid(pid); |
| if (!p) |
| return -ESRCH; |
| |
| if (pid_has_task(p, PIDTYPE_TGID)) |
| fd = pidfd_create(p, flags); |
| else |
| fd = -EINVAL; |
| |
| 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); |
| } |
| |
| static struct file *__pidfd_fget(struct task_struct *task, int fd) |
| { |
| struct file *file; |
| int ret; |
| |
| ret = down_read_killable(&task->signal->exec_update_lock); |
| if (ret) |
| return ERR_PTR(ret); |
| |
| if (ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)) |
| file = fget_task(task, fd); |
| else |
| file = ERR_PTR(-EPERM); |
| |
| up_read(&task->signal->exec_update_lock); |
| |
| return file ?: ERR_PTR(-EBADF); |
| } |
| |
| static int pidfd_getfd(struct pid *pid, int fd) |
| { |
| struct task_struct *task; |
| struct file *file; |
| int ret; |
| |
| task = get_pid_task(pid, PIDTYPE_PID); |
| if (!task) |
| return -ESRCH; |
| |
| file = __pidfd_fget(task, fd); |
| put_task_struct(task); |
| if (IS_ERR(file)) |
| return PTR_ERR(file); |
| |
| ret = receive_fd(file, O_CLOEXEC); |
| fput(file); |
| |
| return ret; |
| } |
| |
| /** |
| * sys_pidfd_getfd() - Get a file descriptor from another process |
| * |
| * @pidfd: the pidfd file descriptor of the process |
| * @fd: the file descriptor number to get |
| * @flags: flags on how to get the fd (reserved) |
| * |
| * This syscall gets a copy of a file descriptor from another process |
| * based on the pidfd, and file descriptor number. It requires that |
| * the calling process has the ability to ptrace the process represented |
| * by the pidfd. The process which is having its file descriptor copied |
| * is otherwise unaffected. |
| * |
| * Return: On success, a cloexec file descriptor is returned. |
| * On error, a negative errno number will be returned. |
| */ |
| SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd, |
| unsigned int, flags) |
| { |
| struct pid *pid; |
| struct fd f; |
| int ret; |
| |
| /* flags is currently unused - make sure it's unset */ |
| if (flags) |
| return -EINVAL; |
| |
| f = fdget(pidfd); |
| if (!f.file) |
| return -EBADF; |
| |
| pid = pidfd_pid(f.file); |
| if (IS_ERR(pid)) |
| ret = PTR_ERR(pid); |
| else |
| ret = pidfd_getfd(pid, fd); |
| |
| fdput(f); |
| return ret; |
| } |