[PATCH] firmware: dmi-sysfs: Fix null-ptr-deref in dmi_sysfs_register_handle

[PATCH] firmware: dmi-sysfs: Fix null-ptr-deref in dmi_sysfs_register_handle

[Chen Zhongjin]

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@huawei.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) {
+		spin_lock(&entry_list_lock);
+		list_del(&entry->list);
+		spin_unlock(&entry_list_lock);
+	}
+
 	kfree(entry);
 }
 
-- 
2.17.1

Re: [PATCH] firmware: dmi-sysfs: Fix null-ptr-deref in dmi_sysfs_register_handle

[Greg KH]

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@huawei.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?

thanks,

greg k-h

Re: [PATCH] firmware: dmi-sysfs: Fix null-ptr-deref in dmi_sysfs_register_handle

[Chen Zhongjin]

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@huawei.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