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![Oleg Nesterov](/assets/img/avatar_default.png)
call_usermodehelper_exec_sync() does fork() + wait() with "unignored"
SIGCHLD. What we have missed is that this worker thread can have other
children previously forked by call_usermodehelper_exec_work() without
UMH_WAIT_PROC. If such a child exits in between it becomes a zombie
because auto-reaping only works if SIGCHLD is ignored, and nobody can
reap it (unless/until this worker thread exits too).
Change the !UMH_WAIT_PROC case to use CLONE_PARENT.
Note: this is only first step. All PF_KTHREAD tasks, even created by
kernel_thread() should have ->parent == kthreadd by default.
Fixes: bb304a5c6f
("kmod: handle UMH_WAIT_PROC from system unbound workqueue")
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
706 lines
19 KiB
C
706 lines
19 KiB
C
/*
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kmod, the new module loader (replaces kerneld)
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Kirk Petersen
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Reorganized not to be a daemon by Adam Richter, with guidance
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from Greg Zornetzer.
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Modified to avoid chroot and file sharing problems.
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Mikael Pettersson
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Limit the concurrent number of kmod modprobes to catch loops from
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"modprobe needs a service that is in a module".
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Keith Owens <kaos@ocs.com.au> December 1999
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Unblock all signals when we exec a usermode process.
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Shuu Yamaguchi <shuu@wondernetworkresources.com> December 2000
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call_usermodehelper wait flag, and remove exec_usermodehelper.
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Rusty Russell <rusty@rustcorp.com.au> Jan 2003
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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/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/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 <asm/uaccess.h>
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#include <trace/events/module.h>
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extern int max_threads;
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#define CAP_BSET (void *)1
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#define CAP_PI (void *)2
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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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#ifdef CONFIG_MODULES
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/*
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modprobe_path is set via /proc/sys.
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*/
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char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
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static void free_modprobe_argv(struct subprocess_info *info)
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{
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kfree(info->argv[3]); /* check call_modprobe() */
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kfree(info->argv);
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}
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static int call_modprobe(char *module_name, int wait)
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{
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struct subprocess_info *info;
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static char *envp[] = {
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"HOME=/",
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"TERM=linux",
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"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
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NULL
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};
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char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
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if (!argv)
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goto out;
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module_name = kstrdup(module_name, GFP_KERNEL);
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if (!module_name)
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goto free_argv;
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argv[0] = modprobe_path;
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argv[1] = "-q";
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argv[2] = "--";
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argv[3] = module_name; /* check free_modprobe_argv() */
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argv[4] = NULL;
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info = call_usermodehelper_setup(modprobe_path, argv, envp, GFP_KERNEL,
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NULL, free_modprobe_argv, NULL);
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if (!info)
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goto free_module_name;
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return call_usermodehelper_exec(info, wait | UMH_KILLABLE);
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free_module_name:
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kfree(module_name);
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free_argv:
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kfree(argv);
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out:
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return -ENOMEM;
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}
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/**
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* __request_module - try to load a kernel module
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* @wait: wait (or not) for the operation to complete
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* @fmt: printf style format string for the name of the module
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* @...: arguments as specified in the format string
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*
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* Load a module using the user mode module loader. The function returns
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* zero on success or a negative errno code or positive exit code from
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* "modprobe" on failure. Note that a successful module load does not mean
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* the module did not then unload and exit on an error of its own. Callers
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* must check that the service they requested is now available not blindly
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* invoke it.
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*
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* If module auto-loading support is disabled then this function
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* becomes a no-operation.
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*/
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int __request_module(bool wait, const char *fmt, ...)
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{
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va_list args;
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char module_name[MODULE_NAME_LEN];
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unsigned int max_modprobes;
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int ret;
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static atomic_t kmod_concurrent = ATOMIC_INIT(0);
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#define MAX_KMOD_CONCURRENT 50 /* Completely arbitrary value - KAO */
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static int kmod_loop_msg;
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/*
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* We don't allow synchronous module loading from async. Module
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* init may invoke async_synchronize_full() which will end up
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* waiting for this task which already is waiting for the module
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* loading to complete, leading to a deadlock.
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*/
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WARN_ON_ONCE(wait && current_is_async());
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if (!modprobe_path[0])
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return 0;
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va_start(args, fmt);
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ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
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va_end(args);
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if (ret >= MODULE_NAME_LEN)
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return -ENAMETOOLONG;
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ret = security_kernel_module_request(module_name);
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if (ret)
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return ret;
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/* If modprobe needs a service that is in a module, we get a recursive
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* loop. Limit the number of running kmod threads to max_threads/2 or
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* MAX_KMOD_CONCURRENT, whichever is the smaller. A cleaner method
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* would be to run the parents of this process, counting how many times
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* kmod was invoked. That would mean accessing the internals of the
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* process tables to get the command line, proc_pid_cmdline is static
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* and it is not worth changing the proc code just to handle this case.
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* KAO.
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*
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* "trace the ppid" is simple, but will fail if someone's
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* parent exits. I think this is as good as it gets. --RR
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*/
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max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
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atomic_inc(&kmod_concurrent);
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if (atomic_read(&kmod_concurrent) > max_modprobes) {
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/* We may be blaming an innocent here, but unlikely */
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if (kmod_loop_msg < 5) {
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printk(KERN_ERR
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"request_module: runaway loop modprobe %s\n",
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module_name);
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kmod_loop_msg++;
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}
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atomic_dec(&kmod_concurrent);
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return -ENOMEM;
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}
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trace_module_request(module_name, wait, _RET_IP_);
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ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
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atomic_dec(&kmod_concurrent);
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return ret;
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}
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EXPORT_SYMBOL(__request_module);
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#endif /* CONFIG_MODULES */
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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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* 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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retval = do_execve(getname_kernel(sub_info->path),
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(const char __user *const __user *)sub_info->argv,
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(const char __user *const __user *)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 sys_wait4 won't populate the status. */
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kernel_sigaction(SIGCHLD, SIG_DFL);
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pid = kernel_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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int ret = -ECHILD;
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/*
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* Normally it is bogus to call wait4() from in-kernel because
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* wait4() wants to write the exit code to a userspace address.
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* But call_usermodehelper_exec_sync() always runs as kernel
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* thread (workqueue) and put_user() to a kernel address works
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* OK for kernel threads, due to their having an mm_segment_t
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* which spans the entire address space.
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*
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* Thus the __user pointer cast is valid here.
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*/
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sys_wait4(pid, (int __user *)&ret, 0, NULL);
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/*
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* If ret is 0, either call_usermodehelper_exec_async failed and
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* the real error code is already in sub_info->retval or
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* sub_info->retval is 0 anyway, so don't mess with it then.
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*/
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if (ret)
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sub_info->retval = ret;
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}
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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 = kernel_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
|
|
* @path: path to usermode executable
|
|
* @argv: arg vector for process
|
|
* @envp: environment for process
|
|
* @gfp_mask: gfp mask for memory allocation
|
|
* @cleanup: a cleanup function
|
|
* @init: an init function
|
|
* @data: arbitrary context sensitive data
|
|
*
|
|
* Returns either %NULL on allocation failure, or a subprocess_info
|
|
* structure. This should be passed to call_usermodehelper_exec to
|
|
* exec the process and free the structure.
|
|
*
|
|
* The init function is used to customize the helper process prior to
|
|
* exec. A non-zero return code causes the process to error out, exit,
|
|
* and return the failure to the calling process
|
|
*
|
|
* The cleanup function is just before ethe subprocess_info is about to
|
|
* be freed. This can be used for freeing the argv and envp. The
|
|
* Function must be runnable in either a process context or the
|
|
* context in which call_usermodehelper_exec is called.
|
|
*/
|
|
struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
|
|
char **envp, gfp_t gfp_mask,
|
|
int (*init)(struct subprocess_info *info, struct cred *new),
|
|
void (*cleanup)(struct subprocess_info *info),
|
|
void *data)
|
|
{
|
|
struct subprocess_info *sub_info;
|
|
sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
|
|
if (!sub_info)
|
|
goto out;
|
|
|
|
INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
|
|
sub_info->path = path;
|
|
sub_info->argv = argv;
|
|
sub_info->envp = envp;
|
|
|
|
sub_info->cleanup = cleanup;
|
|
sub_info->init = init;
|
|
sub_info->data = data;
|
|
out:
|
|
return sub_info;
|
|
}
|
|
EXPORT_SYMBOL(call_usermodehelper_setup);
|
|
|
|
/**
|
|
* call_usermodehelper_exec - start a usermode application
|
|
* @sub_info: information about the subprocessa
|
|
* @wait: wait for the application to finish and return status.
|
|
* when UMH_NO_WAIT don't wait at all, but you get no useful error back
|
|
* when the program couldn't be exec'ed. This makes it safe to call
|
|
* from interrupt context.
|
|
*
|
|
* Runs a user-space application. The application is started
|
|
* asynchronously if wait is not set, and runs as a child of system workqueues.
|
|
* (ie. it runs with full root capabilities and optimized affinity).
|
|
*/
|
|
int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
|
|
{
|
|
DECLARE_COMPLETION_ONSTACK(done);
|
|
int retval = 0;
|
|
|
|
if (!sub_info->path) {
|
|
call_usermodehelper_freeinfo(sub_info);
|
|
return -EINVAL;
|
|
}
|
|
helper_lock();
|
|
if (usermodehelper_disabled) {
|
|
retval = -EBUSY;
|
|
goto out;
|
|
}
|
|
/*
|
|
* Set the completion pointer only if there is a waiter.
|
|
* This makes it possible to use umh_complete to free
|
|
* the data structure in case of UMH_NO_WAIT.
|
|
*/
|
|
sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
|
|
sub_info->wait = wait;
|
|
|
|
queue_work(system_unbound_wq, &sub_info->work);
|
|
if (wait == UMH_NO_WAIT) /* task has freed sub_info */
|
|
goto unlock;
|
|
|
|
if (wait & UMH_KILLABLE) {
|
|
retval = wait_for_completion_killable(&done);
|
|
if (!retval)
|
|
goto wait_done;
|
|
|
|
/* umh_complete() will see NULL and free sub_info */
|
|
if (xchg(&sub_info->complete, NULL))
|
|
goto unlock;
|
|
/* fallthrough, umh_complete() was already called */
|
|
}
|
|
|
|
wait_for_completion(&done);
|
|
wait_done:
|
|
retval = sub_info->retval;
|
|
out:
|
|
call_usermodehelper_freeinfo(sub_info);
|
|
unlock:
|
|
helper_unlock();
|
|
return retval;
|
|
}
|
|
EXPORT_SYMBOL(call_usermodehelper_exec);
|
|
|
|
/**
|
|
* call_usermodehelper() - prepare and start a usermode application
|
|
* @path: path to usermode executable
|
|
* @argv: arg vector for process
|
|
* @envp: environment for process
|
|
* @wait: wait for the application to finish and return status.
|
|
* when UMH_NO_WAIT don't wait at all, but you get no useful error back
|
|
* when the program couldn't be exec'ed. This makes it safe to call
|
|
* from interrupt context.
|
|
*
|
|
* This function is the equivalent to use call_usermodehelper_setup() and
|
|
* call_usermodehelper_exec().
|
|
*/
|
|
int call_usermodehelper(char *path, char **argv, char **envp, int wait)
|
|
{
|
|
struct subprocess_info *info;
|
|
gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
|
|
|
|
info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
|
|
NULL, NULL, NULL);
|
|
if (info == NULL)
|
|
return -ENOMEM;
|
|
|
|
return call_usermodehelper_exec(info, wait);
|
|
}
|
|
EXPORT_SYMBOL(call_usermodehelper);
|
|
|
|
static int proc_cap_handler(struct ctl_table *table, int write,
|
|
void __user *buffer, size_t *lenp, loff_t *ppos)
|
|
{
|
|
struct ctl_table t;
|
|
unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
|
|
kernel_cap_t new_cap;
|
|
int err, i;
|
|
|
|
if (write && (!capable(CAP_SETPCAP) ||
|
|
!capable(CAP_SYS_MODULE)))
|
|
return -EPERM;
|
|
|
|
/*
|
|
* convert from the global kernel_cap_t to the ulong array to print to
|
|
* userspace if this is a read.
|
|
*/
|
|
spin_lock(&umh_sysctl_lock);
|
|
for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) {
|
|
if (table->data == CAP_BSET)
|
|
cap_array[i] = usermodehelper_bset.cap[i];
|
|
else if (table->data == CAP_PI)
|
|
cap_array[i] = usermodehelper_inheritable.cap[i];
|
|
else
|
|
BUG();
|
|
}
|
|
spin_unlock(&umh_sysctl_lock);
|
|
|
|
t = *table;
|
|
t.data = &cap_array;
|
|
|
|
/*
|
|
* 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);
|
|
if (err < 0)
|
|
return err;
|
|
|
|
/*
|
|
* convert from the sysctl array of ulongs to the kernel_cap_t
|
|
* internal representation
|
|
*/
|
|
for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
|
|
new_cap.cap[i] = cap_array[i];
|
|
|
|
/*
|
|
* Drop everything not in the new_cap (but don't add things)
|
|
*/
|
|
spin_lock(&umh_sysctl_lock);
|
|
if (write) {
|
|
if (table->data == CAP_BSET)
|
|
usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
|
|
if (table->data == CAP_PI)
|
|
usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
|
|
}
|
|
spin_unlock(&umh_sysctl_lock);
|
|
|
|
return 0;
|
|
}
|
|
|
|
struct ctl_table usermodehelper_table[] = {
|
|
{
|
|
.procname = "bset",
|
|
.data = CAP_BSET,
|
|
.maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
|
|
.mode = 0600,
|
|
.proc_handler = proc_cap_handler,
|
|
},
|
|
{
|
|
.procname = "inheritable",
|
|
.data = CAP_PI,
|
|
.maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
|
|
.mode = 0600,
|
|
.proc_handler = proc_cap_handler,
|
|
},
|
|
{ }
|
|
};
|