[PATCH 1/1] usermodehelper: check subprocess_info->path != NULL

[Oleg Nesterov <oleg@redhat.com>]

argv_split(empty_or_all_spaces) happily succeeds, it simply returns
argc == 0 and argv[0] == NULL. Change call_usermodehelper_exec() to
check sub_info->path != NULL to avoid the crash.

This is the minimal fix, todo:

	- perhaps we should change argv_split() to return NULL or
	  change the callers.

	- kill or justify ->path[0] check

	- narrow the scope of helper_lock()

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: stable@vger.kernel.org
---
 kernel/kmod.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 1296e72..8241906 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -569,6 +569,11 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
 	int retval = 0;
 
 	helper_lock();
+	if (!sub_info->path) {
+		retval = -EINVAL;
+		goto out;
+	}
+
 	if (sub_info->path[0] == '\0')
 		goto out;
 
-- 
1.5.5.1