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

[Greg KH <gregkh@linuxfoundation.org>]

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