// SPDX-License-Identifier: GPL-2.0 /* * fs/ioprio.c * * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk> * * Helper functions for setting/querying io priorities of processes. The * system calls closely mimmick getpriority/setpriority, see the man page for * those. The prio argument is a composite of prio class and prio data, where * the data argument has meaning within that class. The standard scheduling * classes have 8 distinct prio levels, with 0 being the highest prio and 7 * being the lowest. * * IOW, setting BE scheduling class with prio 2 is done ala: * * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2; * * ioprio_set(PRIO_PROCESS, pid, prio); * * See also Documentation/block/ioprio.rst * */ #include <linux/gfp.h> #include <linux/kernel.h> #include <linux/ioprio.h> #include <linux/cred.h> #include <linux/blkdev.h> #include <linux/capability.h> #include <linux/syscalls.h> #include <linux/security.h> #include <linux/pid_namespace.h> int ioprio_check_cap(int ioprio) { int class = IOPRIO_PRIO_CLASS(ioprio); int data = IOPRIO_PRIO_DATA(ioprio); switch (class) { case IOPRIO_CLASS_RT: /* * Originally this only checked for CAP_SYS_ADMIN, * which was implicitly allowed for pid 0 by security * modules such as SELinux. Make sure we check * CAP_SYS_ADMIN first to avoid a denial/avc for * possibly missing CAP_SYS_NICE permission. */ if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE)) return -EPERM; fallthrough; /* rt has prio field too */ case IOPRIO_CLASS_BE: if (data >= IOPRIO_NR_LEVELS || data < 0) return -EINVAL; break; case IOPRIO_CLASS_IDLE: break; case IOPRIO_CLASS_NONE: if (data) return -EINVAL; break; default: return -EINVAL; } return 0; } SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio) { struct task_struct *p, *g; struct user_struct *user; struct pid *pgrp; kuid_t uid; int ret; ret = ioprio_check_cap(ioprio); if (ret) return ret; ret = -ESRCH; rcu_read_lock(); switch (which) { case IOPRIO_WHO_PROCESS: if (!who) p = current; else p = find_task_by_vpid(who); if (p) ret = set_task_ioprio(p, ioprio); break; case IOPRIO_WHO_PGRP: if (!who) pgrp = task_pgrp(current); else pgrp = find_vpid(who); read_lock(&tasklist_lock); do_each_pid_thread(pgrp, PIDTYPE_PGID, p) { ret = set_task_ioprio(p, ioprio); if (ret) { read_unlock(&tasklist_lock); goto out; } } while_each_pid_thread(pgrp, PIDTYPE_PGID, p); read_unlock(&tasklist_lock); break; case IOPRIO_WHO_USER: uid = make_kuid(current_user_ns(), who); if (!uid_valid(uid)) break; if (!who) user = current_user(); else user = find_user(uid); if (!user) break; for_each_process_thread(g, p) { if (!uid_eq(task_uid(p), uid) || !task_pid_vnr(p)) continue; ret = set_task_ioprio(p, ioprio); if (ret) goto free_uid; } free_uid: if (who) free_uid(user); break; default: ret = -EINVAL; } out: rcu_read_unlock(); return ret; } /* * If the task has set an I/O priority, use that. Otherwise, return * the default I/O priority. * * Expected to be called for current task or with task_lock() held to keep * io_context stable. */ int __get_task_ioprio(struct task_struct *p) { struct io_context *ioc = p->io_context; int prio; if (p != current) lockdep_assert_held(&p->alloc_lock); if (ioc) prio = ioc->ioprio; else prio = IOPRIO_DEFAULT; if (IOPRIO_PRIO_CLASS(prio) == IOPRIO_CLASS_NONE) prio = IOPRIO_PRIO_VALUE(task_nice_ioclass(p), task_nice_ioprio(p)); return prio; } EXPORT_SYMBOL_GPL(__get_task_ioprio); static int get_task_ioprio(struct task_struct *p) { int ret; ret = security_task_getioprio(p); if (ret) goto out; task_lock(p); ret = __get_task_ioprio(p); task_unlock(p); out: return ret; } /* * Return raw IO priority value as set by userspace. We use this for * ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and * also so that userspace can distinguish unset IO priority (which just gets * overriden based on task's nice value) from IO priority set to some value. */ static int get_task_raw_ioprio(struct task_struct *p) { int ret; ret = security_task_getioprio(p); if (ret) goto out; task_lock(p); if (p->io_context) ret = p->io_context->ioprio; else ret = IOPRIO_DEFAULT; task_unlock(p); out: return ret; } static int ioprio_best(unsigned short aprio, unsigned short bprio) { return min(aprio, bprio); } SYSCALL_DEFINE2(ioprio_get, int, which, int, who) { struct task_struct *g, *p; struct user_struct *user; struct pid *pgrp; kuid_t uid; int ret = -ESRCH; int tmpio; rcu_read_lock(); switch (which) { case IOPRIO_WHO_PROCESS: if (!who) p = current; else p = find_task_by_vpid(who); if (p) ret = get_task_raw_ioprio(p); break; case IOPRIO_WHO_PGRP: if (!who) pgrp = task_pgrp(current); else pgrp = find_vpid(who); read_lock(&tasklist_lock); do_each_pid_thread(pgrp, PIDTYPE_PGID, p) { tmpio = get_task_ioprio(p); if (tmpio < 0) continue; if (ret == -ESRCH) ret = tmpio; else ret = ioprio_best(ret, tmpio); } while_each_pid_thread(pgrp, PIDTYPE_PGID, p); read_unlock(&tasklist_lock); break; case IOPRIO_WHO_USER: uid = make_kuid(current_user_ns(), who); if (!who) user = current_user(); else user = find_user(uid); if (!user) break; for_each_process_thread(g, p) { if (!uid_eq(task_uid(p), user->uid) || !task_pid_vnr(p)) continue; tmpio = get_task_ioprio(p); if (tmpio < 0) continue; if (ret == -ESRCH) ret = tmpio; else ret = ioprio_best(ret, tmpio); } if (who) free_uid(user); break; default: ret = -EINVAL; } rcu_read_unlock(); return ret; }