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![Linus Torvalds](/assets/img/avatar_default.png)
The usermodehelper code uses two fake pointers for the two capability cases: CAP_BSET for reading and writing 'usermodehelper_bset', and CAP_PI to read and write 'usermodehelper_inheritable'. This seems to be a completely unnecessary indirection, since we could instead just use the pointers themselves, and never have to do any "if this then that" kind of logic. So just get rid of the fake pointer values, and use the real pointer values instead. Reviewed-by: Luis Chamberlain <mcgrof@kernel.org> Cc: Eric Biederman <ebiederm@xmission.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Kees Cook <keescook@chromium.org> Cc: Iurii Zaikin <yzaikin@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
563 lines
15 KiB
C
563 lines
15 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* umh - the kernel usermode helper
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*/
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/sched/task.h>
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#include <linux/binfmts.h>
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#include <linux/syscalls.h>
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#include <linux/unistd.h>
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#include <linux/kmod.h>
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#include <linux/slab.h>
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#include <linux/completion.h>
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#include <linux/cred.h>
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#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/fs_struct.h>
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#include <linux/workqueue.h>
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#include <linux/security.h>
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#include <linux/mount.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/resource.h>
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#include <linux/notifier.h>
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#include <linux/suspend.h>
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#include <linux/rwsem.h>
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#include <linux/ptrace.h>
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#include <linux/async.h>
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#include <linux/uaccess.h>
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#include <linux/initrd.h>
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#include <linux/freezer.h>
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#include <trace/events/module.h>
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static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
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static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
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static DEFINE_SPINLOCK(umh_sysctl_lock);
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static DECLARE_RWSEM(umhelper_sem);
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static void call_usermodehelper_freeinfo(struct subprocess_info *info)
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{
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if (info->cleanup)
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(*info->cleanup)(info);
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kfree(info);
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}
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static void umh_complete(struct subprocess_info *sub_info)
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{
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struct completion *comp = xchg(&sub_info->complete, NULL);
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/*
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* See call_usermodehelper_exec(). If xchg() returns NULL
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* we own sub_info, the UMH_KILLABLE caller has gone away
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* or the caller used UMH_NO_WAIT.
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*/
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if (comp)
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complete(comp);
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else
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call_usermodehelper_freeinfo(sub_info);
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}
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/*
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* This is the task which runs the usermode application
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*/
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static int call_usermodehelper_exec_async(void *data)
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{
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struct subprocess_info *sub_info = data;
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struct cred *new;
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int retval;
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spin_lock_irq(¤t->sighand->siglock);
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flush_signal_handlers(current, 1);
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spin_unlock_irq(¤t->sighand->siglock);
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/*
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* Initial kernel threads share ther FS with init, in order to
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* get the init root directory. But we've now created a new
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* thread that is going to execve a user process and has its own
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* 'struct fs_struct'. Reset umask to the default.
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*/
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current->fs->umask = 0022;
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/*
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* Our parent (unbound workqueue) runs with elevated scheduling
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* priority. Avoid propagating that into the userspace child.
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*/
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set_user_nice(current, 0);
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retval = -ENOMEM;
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new = prepare_kernel_cred(current);
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if (!new)
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goto out;
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spin_lock(&umh_sysctl_lock);
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new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
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new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
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new->cap_inheritable);
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spin_unlock(&umh_sysctl_lock);
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if (sub_info->init) {
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retval = sub_info->init(sub_info, new);
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if (retval) {
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abort_creds(new);
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goto out;
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}
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}
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commit_creds(new);
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wait_for_initramfs();
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retval = kernel_execve(sub_info->path,
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(const char *const *)sub_info->argv,
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(const char *const *)sub_info->envp);
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out:
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sub_info->retval = retval;
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/*
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* call_usermodehelper_exec_sync() will call umh_complete
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* if UHM_WAIT_PROC.
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*/
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if (!(sub_info->wait & UMH_WAIT_PROC))
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umh_complete(sub_info);
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if (!retval)
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return 0;
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do_exit(0);
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}
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/* Handles UMH_WAIT_PROC. */
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static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
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{
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pid_t pid;
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/* If SIGCLD is ignored do_wait won't populate the status. */
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kernel_sigaction(SIGCHLD, SIG_DFL);
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pid = user_mode_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
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if (pid < 0)
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sub_info->retval = pid;
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else
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kernel_wait(pid, &sub_info->retval);
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/* Restore default kernel sig handler */
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kernel_sigaction(SIGCHLD, SIG_IGN);
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umh_complete(sub_info);
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}
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/*
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* We need to create the usermodehelper kernel thread from a task that is affine
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* to an optimized set of CPUs (or nohz housekeeping ones) such that they
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* inherit a widest affinity irrespective of call_usermodehelper() callers with
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* possibly reduced affinity (eg: per-cpu workqueues). We don't want
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* usermodehelper targets to contend a busy CPU.
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*
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* Unbound workqueues provide such wide affinity and allow to block on
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* UMH_WAIT_PROC requests without blocking pending request (up to some limit).
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*
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* Besides, workqueues provide the privilege level that caller might not have
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* to perform the usermodehelper request.
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*
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*/
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static void call_usermodehelper_exec_work(struct work_struct *work)
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{
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struct subprocess_info *sub_info =
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container_of(work, struct subprocess_info, work);
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if (sub_info->wait & UMH_WAIT_PROC) {
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call_usermodehelper_exec_sync(sub_info);
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} else {
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pid_t pid;
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/*
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* Use CLONE_PARENT to reparent it to kthreadd; we do not
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* want to pollute current->children, and we need a parent
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* that always ignores SIGCHLD to ensure auto-reaping.
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*/
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pid = user_mode_thread(call_usermodehelper_exec_async, sub_info,
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CLONE_PARENT | SIGCHLD);
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if (pid < 0) {
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sub_info->retval = pid;
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umh_complete(sub_info);
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}
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}
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}
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/*
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* If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
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* (used for preventing user land processes from being created after the user
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* land has been frozen during a system-wide hibernation or suspend operation).
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* Should always be manipulated under umhelper_sem acquired for write.
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*/
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static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
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/* Number of helpers running */
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static atomic_t running_helpers = ATOMIC_INIT(0);
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/*
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* Wait queue head used by usermodehelper_disable() to wait for all running
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* helpers to finish.
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*/
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static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
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/*
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* Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
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* to become 'false'.
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*/
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static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
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/*
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* Time to wait for running_helpers to become zero before the setting of
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* usermodehelper_disabled in usermodehelper_disable() fails
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*/
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#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
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int usermodehelper_read_trylock(void)
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{
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DEFINE_WAIT(wait);
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int ret = 0;
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down_read(&umhelper_sem);
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for (;;) {
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prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
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TASK_INTERRUPTIBLE);
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if (!usermodehelper_disabled)
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break;
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if (usermodehelper_disabled == UMH_DISABLED)
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ret = -EAGAIN;
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up_read(&umhelper_sem);
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if (ret)
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break;
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schedule();
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try_to_freeze();
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down_read(&umhelper_sem);
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}
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finish_wait(&usermodehelper_disabled_waitq, &wait);
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return ret;
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}
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EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
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long usermodehelper_read_lock_wait(long timeout)
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{
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DEFINE_WAIT(wait);
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if (timeout < 0)
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return -EINVAL;
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down_read(&umhelper_sem);
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for (;;) {
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prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
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TASK_UNINTERRUPTIBLE);
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if (!usermodehelper_disabled)
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break;
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up_read(&umhelper_sem);
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timeout = schedule_timeout(timeout);
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if (!timeout)
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break;
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down_read(&umhelper_sem);
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}
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finish_wait(&usermodehelper_disabled_waitq, &wait);
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return timeout;
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}
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EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
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void usermodehelper_read_unlock(void)
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{
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up_read(&umhelper_sem);
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}
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EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
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/**
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* __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
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* @depth: New value to assign to usermodehelper_disabled.
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*
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* Change the value of usermodehelper_disabled (under umhelper_sem locked for
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* writing) and wakeup tasks waiting for it to change.
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*/
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void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
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{
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down_write(&umhelper_sem);
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usermodehelper_disabled = depth;
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wake_up(&usermodehelper_disabled_waitq);
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up_write(&umhelper_sem);
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}
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/**
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* __usermodehelper_disable - Prevent new helpers from being started.
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* @depth: New value to assign to usermodehelper_disabled.
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*
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* Set usermodehelper_disabled to @depth and wait for running helpers to exit.
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*/
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int __usermodehelper_disable(enum umh_disable_depth depth)
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{
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long retval;
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if (!depth)
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return -EINVAL;
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down_write(&umhelper_sem);
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usermodehelper_disabled = depth;
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up_write(&umhelper_sem);
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/*
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* From now on call_usermodehelper_exec() won't start any new
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* helpers, so it is sufficient if running_helpers turns out to
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* be zero at one point (it may be increased later, but that
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* doesn't matter).
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*/
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retval = wait_event_timeout(running_helpers_waitq,
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atomic_read(&running_helpers) == 0,
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RUNNING_HELPERS_TIMEOUT);
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if (retval)
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return 0;
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__usermodehelper_set_disable_depth(UMH_ENABLED);
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return -EAGAIN;
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}
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static void helper_lock(void)
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{
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atomic_inc(&running_helpers);
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smp_mb__after_atomic();
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}
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static void helper_unlock(void)
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{
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if (atomic_dec_and_test(&running_helpers))
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wake_up(&running_helpers_waitq);
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}
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/**
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* call_usermodehelper_setup - prepare to call a usermode helper
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* @path: path to usermode executable
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* @argv: arg vector for process
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* @envp: environment for process
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* @gfp_mask: gfp mask for memory allocation
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* @init: an init function
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* @cleanup: a cleanup function
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* @data: arbitrary context sensitive data
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*
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* Returns either %NULL on allocation failure, or a subprocess_info
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* structure. This should be passed to call_usermodehelper_exec to
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* exec the process and free the structure.
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*
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* The init function is used to customize the helper process prior to
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* exec. A non-zero return code causes the process to error out, exit,
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* and return the failure to the calling process
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*
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* The cleanup function is just before the subprocess_info is about to
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* be freed. This can be used for freeing the argv and envp. The
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* Function must be runnable in either a process context or the
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* context in which call_usermodehelper_exec is called.
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*/
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struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
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char **envp, gfp_t gfp_mask,
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int (*init)(struct subprocess_info *info, struct cred *new),
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void (*cleanup)(struct subprocess_info *info),
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void *data)
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{
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struct subprocess_info *sub_info;
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sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
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if (!sub_info)
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goto out;
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INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
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#ifdef CONFIG_STATIC_USERMODEHELPER
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sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
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#else
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sub_info->path = path;
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#endif
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sub_info->argv = argv;
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sub_info->envp = envp;
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sub_info->cleanup = cleanup;
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sub_info->init = init;
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sub_info->data = data;
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out:
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return sub_info;
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}
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EXPORT_SYMBOL(call_usermodehelper_setup);
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/**
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* call_usermodehelper_exec - start a usermode application
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* @sub_info: information about the subprocess
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* @wait: wait for the application to finish and return status.
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* when UMH_NO_WAIT don't wait at all, but you get no useful error back
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* when the program couldn't be exec'ed. This makes it safe to call
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* from interrupt context.
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*
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* Runs a user-space application. The application is started
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* asynchronously if wait is not set, and runs as a child of system workqueues.
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* (ie. it runs with full root capabilities and optimized affinity).
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*
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* Note: successful return value does not guarantee the helper was called at
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* all. You can't rely on sub_info->{init,cleanup} being called even for
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* UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers
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* into a successful no-op.
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*/
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int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
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{
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unsigned int state = TASK_UNINTERRUPTIBLE;
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DECLARE_COMPLETION_ONSTACK(done);
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int retval = 0;
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if (!sub_info->path) {
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call_usermodehelper_freeinfo(sub_info);
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return -EINVAL;
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}
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helper_lock();
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if (usermodehelper_disabled) {
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retval = -EBUSY;
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goto out;
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}
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/*
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* If there is no binary for us to call, then just return and get out of
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* here. This allows us to set STATIC_USERMODEHELPER_PATH to "" and
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* disable all call_usermodehelper() calls.
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*/
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if (strlen(sub_info->path) == 0)
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goto out;
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/*
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* Set the completion pointer only if there is a waiter.
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* This makes it possible to use umh_complete to free
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* the data structure in case of UMH_NO_WAIT.
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*/
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sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
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sub_info->wait = wait;
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queue_work(system_unbound_wq, &sub_info->work);
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if (wait == UMH_NO_WAIT) /* task has freed sub_info */
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goto unlock;
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if (wait & UMH_FREEZABLE)
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state |= TASK_FREEZABLE;
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if (wait & UMH_KILLABLE) {
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retval = wait_for_completion_state(&done, state | TASK_KILLABLE);
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if (!retval)
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goto wait_done;
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/* umh_complete() will see NULL and free sub_info */
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if (xchg(&sub_info->complete, NULL))
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goto unlock;
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/*
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* fallthrough; in case of -ERESTARTSYS now do uninterruptible
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* wait_for_completion_state(). Since umh_complete() shall call
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* complete() in a moment if xchg() above returned NULL, this
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* uninterruptible wait_for_completion_state() will not block
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* SIGKILL'ed processes for long.
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*/
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}
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wait_for_completion_state(&done, state);
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wait_done:
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retval = sub_info->retval;
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out:
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call_usermodehelper_freeinfo(sub_info);
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unlock:
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helper_unlock();
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return retval;
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}
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EXPORT_SYMBOL(call_usermodehelper_exec);
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/**
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* call_usermodehelper() - prepare and start a usermode application
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* @path: path to usermode executable
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* @argv: arg vector for process
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* @envp: environment for process
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* @wait: wait for the application to finish and return status.
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* when UMH_NO_WAIT don't wait at all, but you get no useful error back
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* when the program couldn't be exec'ed. This makes it safe to call
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* from interrupt context.
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*
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* This function is the equivalent to use call_usermodehelper_setup() and
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* call_usermodehelper_exec().
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*/
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int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
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{
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struct subprocess_info *info;
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gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
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info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
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NULL, NULL, NULL);
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if (info == NULL)
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return -ENOMEM;
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return call_usermodehelper_exec(info, wait);
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}
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EXPORT_SYMBOL(call_usermodehelper);
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static int proc_cap_handler(struct ctl_table *table, int write,
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void *buffer, size_t *lenp, loff_t *ppos)
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|
{
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|
struct ctl_table t;
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|
unsigned long cap_array[2];
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kernel_cap_t new_cap, *cap;
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int err;
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|
|
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if (write && (!capable(CAP_SETPCAP) ||
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|
!capable(CAP_SYS_MODULE)))
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return -EPERM;
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|
|
|
/*
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* convert from the global kernel_cap_t to the ulong array to print to
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|
* userspace if this is a read.
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|
*
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|
* Legacy format: capabilities are exposed as two 32-bit values
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|
*/
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cap = table->data;
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spin_lock(&umh_sysctl_lock);
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cap_array[0] = (u32) cap->val;
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cap_array[1] = cap->val >> 32;
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|
spin_unlock(&umh_sysctl_lock);
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|
|
|
t = *table;
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|
t.data = &cap_array;
|
|
|
|
/*
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|
* actually read or write and array of ulongs from userspace. Remember
|
|
* these are least significant 32 bits first
|
|
*/
|
|
err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
|
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if (err < 0)
|
|
return err;
|
|
|
|
new_cap.val = (u32)cap_array[0];
|
|
new_cap.val += (u64)cap_array[1] << 32;
|
|
|
|
/*
|
|
* Drop everything not in the new_cap (but don't add things)
|
|
*/
|
|
if (write) {
|
|
spin_lock(&umh_sysctl_lock);
|
|
*cap = cap_intersect(*cap, new_cap);
|
|
spin_unlock(&umh_sysctl_lock);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
struct ctl_table usermodehelper_table[] = {
|
|
{
|
|
.procname = "bset",
|
|
.data = &usermodehelper_bset,
|
|
.maxlen = 2 * sizeof(unsigned long),
|
|
.mode = 0600,
|
|
.proc_handler = proc_cap_handler,
|
|
},
|
|
{
|
|
.procname = "inheritable",
|
|
.data = &usermodehelper_inheritable,
|
|
.maxlen = 2 * sizeof(unsigned long),
|
|
.mode = 0600,
|
|
.proc_handler = proc_cap_handler,
|
|
},
|
|
{ }
|
|
};
|