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bf956be520
kasan reported use-after-free:
BUG: KASAN: use-after-free in call_usermodehelper_exec_work+0x2d3/0x310 kernel/umh.c:195
Write of size 4 at addr ffff8801d9202370 by task kworker/u4:2/50
Workqueue: events_unbound call_usermodehelper_exec_work
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1b9/0x294 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
__asan_report_store4_noabort+0x17/0x20 mm/kasan/report.c:437
call_usermodehelper_exec_work+0x2d3/0x310 kernel/umh.c:195
process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
The reason is that 'sub_info' cannot be accessed out of parent task
context, since it will be freed by the child.
Instead remember the pid in the child task.
Fixes: 449325b52b
("umh: introduce fork_usermode_blob() helper")
Reported-by: syzbot+2c73319c406f1987d156@syzkaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
687 lines
18 KiB
C
687 lines
18 KiB
C
/*
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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/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/shmem_fs.h>
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#include <linux/pipe_fs_i.h>
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#include <trace/events/module.h>
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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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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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sub_info->pid = task_pid_nr(current);
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if (sub_info->file)
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retval = do_execve_file(sub_info->file,
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sub_info->argv, sub_info->envp);
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else
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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 kernel_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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kernel_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
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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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* @cleanup: a cleanup function
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* @init: an init 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 ethe 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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struct subprocess_info *call_usermodehelper_setup_file(struct file *file,
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int (*init)(struct subprocess_info *info, struct cred *new),
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void (*cleanup)(struct subprocess_info *info), 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_KERNEL);
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if (!sub_info)
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return NULL;
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INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
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sub_info->path = "none";
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sub_info->file = file;
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sub_info->init = init;
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sub_info->cleanup = cleanup;
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sub_info->data = data;
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return sub_info;
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}
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static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
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{
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struct umh_info *umh_info = info->data;
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struct file *from_umh[2];
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struct file *to_umh[2];
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int err;
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/* create pipe to send data to umh */
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err = create_pipe_files(to_umh, 0);
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if (err)
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return err;
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err = replace_fd(0, to_umh[0], 0);
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fput(to_umh[0]);
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if (err < 0) {
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fput(to_umh[1]);
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return err;
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}
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/* create pipe to receive data from umh */
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err = create_pipe_files(from_umh, 0);
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if (err) {
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fput(to_umh[1]);
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replace_fd(0, NULL, 0);
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return err;
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}
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err = replace_fd(1, from_umh[1], 0);
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fput(from_umh[1]);
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if (err < 0) {
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fput(to_umh[1]);
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replace_fd(0, NULL, 0);
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fput(from_umh[0]);
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return err;
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}
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umh_info->pipe_to_umh = to_umh[1];
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umh_info->pipe_from_umh = from_umh[0];
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return 0;
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}
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static void umh_save_pid(struct subprocess_info *info)
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{
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struct umh_info *umh_info = info->data;
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umh_info->pid = info->pid;
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}
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/**
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* fork_usermode_blob - fork a blob of bytes as a usermode process
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* @data: a blob of bytes that can be do_execv-ed as a file
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* @len: length of the blob
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* @info: information about usermode process (shouldn't be NULL)
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*
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* Returns either negative error or zero which indicates success
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* in executing a blob of bytes as a usermode process. In such
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* case 'struct umh_info *info' is populated with two pipes
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* and a pid of the process. The caller is responsible for health
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* check of the user process, killing it via pid, and closing the
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* pipes when user process is no longer needed.
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*/
|
|
int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
|
|
{
|
|
struct subprocess_info *sub_info;
|
|
struct file *file;
|
|
ssize_t written;
|
|
loff_t pos = 0;
|
|
int err;
|
|
|
|
file = shmem_kernel_file_setup("", len, 0);
|
|
if (IS_ERR(file))
|
|
return PTR_ERR(file);
|
|
|
|
written = kernel_write(file, data, len, &pos);
|
|
if (written != len) {
|
|
err = written;
|
|
if (err >= 0)
|
|
err = -ENOMEM;
|
|
goto out;
|
|
}
|
|
|
|
err = -ENOMEM;
|
|
sub_info = call_usermodehelper_setup_file(file, umh_pipe_setup,
|
|
umh_save_pid, info);
|
|
if (!sub_info)
|
|
goto out;
|
|
|
|
err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
|
|
out:
|
|
fput(file);
|
|
return err;
|
|
}
|
|
EXPORT_SYMBOL_GPL(fork_usermode_blob);
|
|
|
|
/**
|
|
* 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;
|
|
}
|
|
|
|
/*
|
|
* If there is no binary for us to call, then just return and get out of
|
|
* here. This allows us to set STATIC_USERMODEHELPER_PATH to "" and
|
|
* disable all call_usermodehelper() calls.
|
|
*/
|
|
if (strlen(sub_info->path) == 0)
|
|
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(const 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)
|
|
*/
|
|
if (write) {
|
|
spin_lock(&umh_sysctl_lock);
|
|
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,
|
|
},
|
|
{ }
|
|
};
|