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kernel: add a kernel_wait helper

Add a helper that waits for a pid and stores the status in the passed in kernel pointer. Use it to fix the usage of kernel_wait4 in call_usermodehelper_exec_sync that only happens to work due to the implicit set_fs(KERNEL_DS) for kernel threads.

Christoph Hellwig committed 6 years ago

Commit 8043fc11 parent f48ff833 files · +21 −25Browse files

Unified · Split

3 files
  1. include/linux/sched/task.h +1 −0
  2. kernel/exit.c +16 −0
  3. kernel/umh.c +4 −25
include/linux/sched/task.h+1−0
@@ -88,6 +88,7 @@ struct task_struct *fork_idle(int); · 87 unmodified lines
88struct mm_struct *copy_init_mm(void);88struct mm_struct *copy_init_mm(void);
89extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);89extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
90extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);90extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
91int kernel_wait(pid_t pid, int *stat);
91 92
92extern void free_task(struct task_struct *tsk);93extern void free_task(struct task_struct *tsk);
93 94
kernel/exit.c+16−0
@@ -1626,6 +1626,22 @@ long kernel_wait4(pid_t upid, int __user *stat_addr, int options, · 1625 unmodified lines
1626 return ret;1626 return ret;
1627}1627}
1628 1628
1629int kernel_wait(pid_t pid, int *stat)
1630{
1631 struct wait_opts wo = {
1632 .wo_type = PIDTYPE_PID,
1633 .wo_pid = find_get_pid(pid),
1634 .wo_flags = WEXITED,
1635 };
1636 int ret;
1637
1638 ret = do_wait(&wo);
1639 if (ret > 0 && wo.wo_stat)
1640 *stat = wo.wo_stat;
1641 put_pid(wo.wo_pid);
1642 return ret;
1643}
1644
1629SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,1645SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
1630 int, options, struct rusage __user *, ru)1646 int, options, struct rusage __user *, ru)
1631{1647{
kernel/umh.c+4−25
@@ -119,37 +119,16 @@ static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info) · 118 unmodified lines
119{119{
120 pid_t pid;120 pid_t pid;
121 121
122 /* If SIGCLD is ignored kernel_wait4 won't populate the status. */122 /* If SIGCLD is ignored do_wait won't populate the status. */
123 kernel_sigaction(SIGCHLD, SIG_DFL);123 kernel_sigaction(SIGCHLD, SIG_DFL);
124 pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);124 pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
125 if (pid < 0) {125 if (pid < 0)
126 sub_info->retval = pid;126 sub_info->retval = pid;
127 } else {127 else
128 int ret = -ECHILD;128 kernel_wait(pid, &sub_info->retval);
129 /*
130 * Normally it is bogus to call wait4() from in-kernel because
131 * wait4() wants to write the exit code to a userspace address.
132 * But call_usermodehelper_exec_sync() always runs as kernel
133 * thread (workqueue) and put_user() to a kernel address works
134 * OK for kernel threads, due to their having an mm_segment_t
135 * which spans the entire address space.
136 *
137 * Thus the __user pointer cast is valid here.
138 */
139 kernel_wait4(pid, (int __user *)&ret, 0, NULL);
140
141 /*
142 * If ret is 0, either call_usermodehelper_exec_async failed and
143 * the real error code is already in sub_info->retval or
144 * sub_info->retval is 0 anyway, so don't mess with it then.
145 */
146 if (ret)
147 sub_info->retval = ret;
148 }
149 129
150 /* Restore default kernel sig handler */130 /* Restore default kernel sig handler */
151 kernel_sigaction(SIGCHLD, SIG_IGN);131 kernel_sigaction(SIGCHLD, SIG_IGN);
152
153 umh_complete(sub_info);132 umh_complete(sub_info);
154}133}
155 134