wait_for_helper: SIGCHLD from user-space can lead to use-after-free

[deliverable/linux.git] / kernel / kmod.c

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 7efba6f8e3ec9dfaca8dbc6cb0222f7e9cb13250..48daed4c51bab67926c881d588ae112895f41404 100644 (file)
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -175,16 +175,16 @@ static int wait_for_helper(void *data)
        struct subprocess_info *sub_info = data;
        pid_t pid;
 
-       /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
-        * populate the status, but will return -ECHILD. */
-       allow_signal(SIGCHLD);
+       /* If SIGCLD is ignored sys_wait4 won't populate the status. */
+       spin_lock_irq(&current->sighand->siglock);
+       current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
+       spin_unlock_irq(&current->sighand->siglock);
 
        pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
        if (pid < 0) {
                sub_info->retval = pid;
        } else {
-               int ret;
-
+               int ret = -ECHILD;
                /*
                 * Normally it is bogus to call wait4() from in-kernel because
                 * wait4() wants to write the exit code to a userspace address.