linux-kernel - Re: [PATCH] kmod: Check for NULL at call_usermodehelper

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Date:	Mon, 23 Sep 2013 14:30:57 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	oleg@...hat.com, viro@...iv.linux.org.uk, rostedt@...dmis.org,
	fweisbec@...il.com, mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kmod: Check for NULL at call_usermodehelper_exec().

On Tue, 24 Sep 2013 06:12:34 +0900 Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> wrote:

> Andrew, would you pick up this patch?
> 
> Regards.
> ----------
> >From d6ff218545060c5f8b75b15d5b34bffcf625508f Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Mon, 16 Sep 2013 02:19:10 +0900
> Subject: [PATCH] kmod: Check for NULL at call_usermodehelper_exec().
> 
> If /proc/sys/kernel/core_pattern contains only "|", NULL pointer dereference
> happens upon core dump because argv_split("") returns argv[0] == NULL.
> 
> This bug was once fixed by commit 264b83c0 "usermodehelper: check
> subprocess_info->path != NULL" but was by error reintroduced by commit
> 7f57cfa4 "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).
> 
> ...
>
> --- a/kernel/kmod.c
> +++ b/kernel/kmod.c
> @@ -571,6 +571,10 @@ 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 -ENOENT;
> +	}
>  	helper_lock();
>  	if (!khelper_wq || usermodehelper_disabled) {
>  		retval = -EBUSY;

The error is that the user put a bare "|" into
/proc/sys/kernel/core_pattern.  Is ENOENT ("No such file or directory")
the most appropriate error code here?  I think EINVAL ("Invalid
argument")?

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