Re: [PATCH RFC] ubi: gluebi: Fix NULL pointer dereference caused by ftl notifier

[Zhihao Cheng <chengzhihao1@huawei.com>]

在 2023/10/12 17:31, ZhaoLong Wang 写道:
> 
>>>
>>>> 3.         P1                    P2
>>>>     gluebi_create -> mtd_device_register -> add_mtd_device:
>>>>     device_register   // dev/mtd1 is visible
>>>>
>>>>                       fd = open(/dev/mtd1, O_WRONLY)
>>>>                        gluebi_get_device
>>>>                         gluebi->desc = ubi_open_volume
>>>>
>>>>     ftl_add_mtd
>>>>      mtd_read
>>>>       gluebi_read
>>>>        gluebi->desc is not ERR_PTR/NULL
>>>>
>>>>                      close(fd)
>>>>                       gluebi_put_device
>>>>                        ubi_close_volume
>>>>                         kfree(desc)
>>>>        ubi_read(gluebi->desc)   // UAF  (×)
>>>>
>>>
>>> Yes, it's also a problem. Perhaps it should be set to NULL after
>>> destroying gluebi->desc.
>>
>> The key point is that 'gluebi->desc' check & usage is not atomic in 
>> gluebi_read. So following patch still can't handle situation 3.
>>
> 
> Setting the desc to NULL works because
> mutex_lock "mtd_table_mutex" is held on all paths where
> ftl_add_mtd() is called.
> 

Oh, you're right. Just one nit below:


 > @@ -154,9 +159,26 @@ static int gluebi_read(struct mtd_info *mtd, loff_t
 > from, size_t len,
 >                  size_t *retlen, unsigned char *buf)
 >   {
 >       int err = 0, lnum, offs, bytes_left;
 > -    struct gluebi_device *gluebi;
 > +    struct gluebi_device *gluebi = container_of(mtd, struct 
gluebi_device,
 > +                            mtd);
 > +    int isnt_get = unlikely(gluebi->desc == NULL) ? 1 : 0;

This 'unlikey' can be removed.

Rename 'isnt_get' as 'has_desc' ?

 > +    /**
 > +     * In normal case, the UBI volume desc has been initialized by
 > +     * ->_get_device(). However, in the ftl notifier process, the
 > +     * ->_get_device() is not executed in advance and the MTD device
 > +     * is directly scanned  which cause null pointe dereference.
 > +     * Therefore, try to get the MTD device here.
 > +     */
 > +    if (unlikely(isnt_get)) {
 > +        err = __get_mtd_device(mtd);
 > +        if (err) {
 > +            err_msg("cannot get MTD device %d, UBI device %d, volume
 > %d, error %d",
 > +                mtd->index, gluebi->ubi_num, gluebi->vol_id, err);
 > +            return err;
 > +        }
 > +    }