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.
Showing the changes to kernel (2 of 3 files). Show all
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| @@ -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 | ||
| 1629 | int 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 | |||
| 1629 | SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr, | 1645 | SYSCALL_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 | { |
| @@ -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 | ||