[ 3.8.y.z extended stable ] Patch "kernel/kmod.c: check for NULL in call_usermodehelper_exec()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    kernel/kmod.c: check for NULL in call_usermodehelper_exec()

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From c40923662ca8a768b5c99a382179e9b28ca7ecab Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Date: Mon, 30 Sep 2013 13:45:08 -0700
Subject: kernel/kmod.c: check for NULL in call_usermodehelper_exec()

commit 4c1c7be95c345cf2ad537a0c48e9aeadc7304527 upstream.

If /proc/sys/kernel/core_pattern contains only "|", a NULL pointer
dereference happens upon core dump because argv_split("") returns
argv[0] == NULL.

This bug was once fixed by commit 264b83c07a84 ("usermodehelper: check
subprocess_info->path != NULL") but was by error reintroduced by commit
7f57cfa4e2aa ("usermodehelper: kill the sub_info->path[0] check").

This bug seems to exist since 2.6.19 (the version which core dump to
pipe was added).  Depending on kernel version and config, some side
effect might happen immediately after this oops (e.g.  kernel panic with
2.6.32-358.18.1.el6).

Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Acked-by: Oleg Nesterov <oleg at redhat.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/kmod.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 41e1524..6444887 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -560,6 +560,10 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
 	DECLARE_COMPLETION_ONSTACK(done);
 	int retval = 0;

+	if (!sub_info->path) {
+		call_usermodehelper_freeinfo(sub_info);
+		return -EINVAL;
+	}
 	helper_lock();
 	if (!sub_info->path) {
 		retval = -EINVAL;
--
1.8.1.2