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SubjectRe: input0: bad kobj_uevent_env content in show_uevent()
Date
Fengguang Wu <fengguang.wu@intel.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:


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)



Bjørn
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