linux-kernel - [ 116/135] kobject: fix oops with "input0: bad kobj_uevent_env content in show

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Message-Id: <20120917003642.279358860@decadent.org.uk>
Date:	Mon, 17 Sep 2012 01:38:21 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	Bjørn Mork <bjorn@...k.no>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [ 116/135] kobject: fix oops with "input0: bad kobj_uevent_env content in
 show_uevent()"

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bjørn Mork <bjorn@...k.no>

commit 60e233a56609fd963c59e99bd75c663d63fa91b6 upstream.

Fengguang Wu <fengguang.wu@...el.com> writes:

> After the __devinit* removal series, I can still get kernel panic in
> show_uevent(). So there are more sources of bug..
>
> Debug patch:
>
> @@ -343,8 +343,11 @@ static ssize_t show_uevent(struct device
>                 goto out;
>
>         /* copy keys to file */
> -       for (i = 0; i < env->envp_idx; i++)
> +       dev_err(dev, "uevent %d env[%d]: %s/.../%s\n", env->buflen, env->envp_idx, top_kobj->name, dev->kobj.name);
> +       for (i = 0; i < env->envp_idx; i++) {
> +               printk(KERN_ERR "uevent %d env[%d]: %s\n", (int)count, i, env->envp[i]);
>                 count += sprintf(&buf[count], "%s\n", env->envp[i]);
> +       }
>
> Oops message, the env[] is again not properly initilized:
>
> [   44.068623] input input0: uevent 61 env[805306368]: input0/.../input0
> [   44.069552] uevent 0 env[0]: (null)

This is a completely different CONFIG_HOTPLUG problem, only
demonstrating another reason why CONFIG_HOTPLUG should go away.  I had a
hard time trying to disable it anyway ;-)

The problem this time is lots of code assuming that a call to
add_uevent_var() will guarantee that env->buflen > 0.  This is not true
if CONFIG_HOTPLUG is unset.  So things like this end up overwriting
env->envp_idx because the array index is -1:

	if (add_uevent_var(env, "MODALIAS="))
		return -ENOMEM;
        len = input_print_modalias(&env->buf[env->buflen - 1],
				   sizeof(env->buf) - env->buflen,
				   dev, 0);

Don't know what the best action is, given that there seem to be a *lot*
of this around the kernel.  This patch "fixes" the problem for me, but I
don't know if it can be considered an appropriate fix.

[ It is the correct fix for now, for 3.7 forcing CONFIG_HOTPLUG to
always be on is the longterm fix, but it's too late for 3.6 and older
kernels to resolve this that way - gregkh ]

Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: Bjørn Mork <bjorn@...k.no>
Tested-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/linux/kobject.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index fc615a9..1e57449 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -224,7 +224,7 @@ static inline int kobject_uevent_env(struct kobject *kobj,
 
 static inline __printf(2, 3)
 int add_uevent_var(struct kobj_uevent_env *env, const char *format, ...)
-{ return 0; }
+{ return -ENOMEM; }
 
 static inline int kobject_action_type(const char *buf, size_t count,
 				      enum kobject_action *type)


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