linux-kernel - Re: [PATCH] firmware: dmi-sysfs: Fix null-ptr-deref in dmi_sysfs_register

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Date:   Fri, 11 Nov 2022 09:19:00 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <linmq006@...il.com>
Subject: Re: [PATCH] firmware: dmi-sysfs: Fix null-ptr-deref in
 dmi_sysfs_register_handle

Hi,

On 2022/11/11 1:49, Greg KH wrote:
> On Mon, Oct 17, 2022 at 05:53:42PM +0800, Chen Zhongjin wrote:
>> KASAN reported a null-ptr-deref error:
>>
>> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
>> CPU: 0 PID: 1373 Comm: modprobe
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
>> RIP: 0010:dmi_sysfs_entry_release
>> ...
>> Call Trace:
>>   <TASK>
>>   kobject_put
>>   dmi_sysfs_register_handle (drivers/firmware/dmi-sysfs.c:540) dmi_sysfs
>>   dmi_decode_table (drivers/firmware/dmi_scan.c:133)
>>   dmi_walk (drivers/firmware/dmi_scan.c:1115)
>>   dmi_sysfs_init (drivers/firmware/dmi-sysfs.c:149) dmi_sysfs
>>   do_one_initcall (init/main.c:1296)
>>   ...
>> Kernel panic - not syncing: Fatal exception
>> Kernel Offset: 0x4000000 from 0xffffffff81000000
>> ---[ end Kernel panic - not syncing: Fatal exception ]---
>>
>> It is because previous patch added kobject_put() to release the memory
>> which will call  dmi_sysfs_entry_release() and list_del().
>>
>> However, list_add_tail(entry->list) is called after the error block,
>> so the list_head is uninitialized and cannot be deleted.
>>
>> Because entry is allocated by kzalloc() so the list.prev is NULL in
>> the error path. Check it in dmi_sysfs_entry_release() to avoid
>> deleting uninitialized list_head.
>>
>> Fixes: 660ba678f999 ("firmware: dmi-sysfs: Fix memory leak in dmi_sysfs_register_handle")
>>
>> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
>> ---
>>   drivers/firmware/dmi-sysfs.c | 9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
>> index 66727ad3361b..f8815eeed00c 100644
>> --- a/drivers/firmware/dmi-sysfs.c
>> +++ b/drivers/firmware/dmi-sysfs.c
>> @@ -557,9 +557,12 @@ static void dmi_sysfs_entry_release(struct kobject *kobj)
>>   {
>>   	struct dmi_sysfs_entry *entry = to_entry(kobj);
>>   
>> -	spin_lock(&entry_list_lock);
>> -	list_del(&entry->list);
>> -	spin_unlock(&entry_list_lock);
>> +	if (entry->list.prev != NULL) {
> You should not be poking around in a lock structure like this at all.
> Also the lock isn't held, so how do you know this is going to work?
>
> I suggest fixing up the original patch, perhaps reverting that instead?

It makes sense, but in fact the original patch did fix the memory leak.

I'm going to move kobject_put behind list_add_tail to keep consistency, 
because only after that the
entry initialization is complete.

Will send v2, thanks for your review!


Best,

Chen

> thanks,
>
> greg k-h