[PATCH] Fix ____call_usermodehelper errors being silently ignored

If ____call_usermodehelper fails, we're not interested in the child
process' exit value, but the real error, so let's stop wait_for_helper from
overwriting it in that case.

Issue discovered by Benedikt Böhm while working on a Linux-VServer usermode
helper.

Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 5c470c57fb57..842f8015d7fd 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -176,6 +176,8 @@ static int wait_for_helper(void *data)
         if (pid < 0) {
                 sub_info->retval = pid;
         } else {
+                int ret;
+
                 /*
                  * Normally it is bogus to call wait4() from in-kernel because
                  * wait4() wants to write the exit code to a userspace address.
@@ -185,7 +187,15 @@ static int wait_for_helper(void *data)
                  *
                  * Thus the __user pointer cast is valid here.
                  */
-                sys_wait4(pid, (int __user *) &sub_info->retval, 0, NULL);
+                sys_wait4(pid, (int __user *)&ret, 0, NULL);
+
+                /*
+                 * If ret is 0, either ____call_usermodehelper failed and the
+                 * real error code is already in sub_info->retval or
+                 * sub_info->retval is 0 anyway, so don't mess with it then.
+                 */
+                if (ret)
+                        sub_info->retval = ret;
         }
 
         complete(sub_info->complete);