[alsa-devel] [PATCH] ALSA: hda: check RIRB to avoid use NULL pointer

[Liwei Song]

On 04/30/2019 03:31 PM, Takashi Iwai wrote:
> On Tue, 30 Apr 2019 08:10:53 +0200,
> Song liwei wrote:
>>
>> From: Liwei Song <liwei.song at windriver.com>
>>
>> Fix the following BUG:
>>
>> BUG: unable to handle kernel NULL pointer dereference at 000000000000000c
>> Workqueue: events azx_probe_work [snd_hda_intel]
>> RIP: 0010:snd_hdac_bus_update_rirb+0x80/0x160 [snd_hda_core]
>> Call Trace:
>>  <IRQ>
>>  azx_interrupt+0x78/0x140 [snd_hda_codec]
>>  __handle_irq_event_percpu+0x49/0x300
>>  handle_irq_event_percpu+0x23/0x60
>>  handle_irq_event+0x3c/0x60
>>  handle_edge_irq+0xdb/0x180
>>  handle_irq+0x23/0x30
>>  do_IRQ+0x6a/0x140
>>  common_interrupt+0xf/0xf
>>
>> The Call Trace happened when run kdump on a NFS rootfs system.
>> Exist the following calling sequence when boot the second kernel:
>>
>> azx_first_init()
>>    --> azx_acquire_irq()
>>                       <-- interrupt come in, azx_interrupt() was called
>>    --> hda_intel_init_chip()
>>       --> azx_init_chip()
>>          --> snd_hdac_bus_init_chip()
>>               --> snd_hdac_bus_init_cmd_io();
>>                     --> init rirb.buf and corb.buf
>>
>> Interrupt happened after azx_acquire_irq() while RIRB still didn't got
>> initialized, then NULL pointer will be used when process the interrupt.
>>
>> Check the value of RIRB to ensure it is not NULL, to aviod some special
>> case may hang the system.
>>
>> Fixes: 14752412721c ("ALSA: hda - Add the controller helper codes to hda-core module")
>> Signed-off-by: Liwei Song <liwei.song at windriver.com>
> 
> Oh, that's indeed a race there.
> 
> But I guess the check introduced by the patch is still error-prone.
> Basically the interrupt handling should be moved after the chip
> initialization.  I suppose that your platform uses the shared
> interrupt, not the MSI?

This is the information from /proc/interrupt
134:          0        102          0          0  IR-PCI-MSI 514048-edge      snd_hda_intel:card0


> 
> In anyway, alternative (and likely more certain) fix would be to move
> the azx_acquir_irq() call like the patch below (note: totally
> untested).  Could you check whether it works?

Yes, It works.

Considering a previous patch like the one you provide will import some issue, 
so I choose check the invalid value to low the risk, but just as you mentioned,
It is not a good solution.

commit 542cedec53c9e8b73f3f05bf8468823598c50489
Author: Yu Zhao <yuzhao at google.com>
Date:   Tue Sep 11 15:12:46 2018 -0600

    Revert "ASoC: Intel: Skylake: Acquire irq after RIRB allocation"
    
    This reverts commit 12eeeb4f4733bbc4481d01df35933fc15beb8b19.
    
    The patch doesn't fix accessing memory with null pointer in
    skl_interrupt().
    
    There are two problems: 1) skl_init_chip() is called twice, before
    and after dma buffer is allocate. The first call sets bus->chip_init
    which prevents the second from initializing bus->corb.buf and
    rirb.buf from bus->rb.area. 2) snd_hdac_bus_init_chip() enables
    interrupt before snd_hdac_bus_init_cmd_io() initializing dma buffers.
    There is a small window which skl_interrupt() can be called if irq
    has been acquired. If so, it crashes when using null dma buffer
    pointers.

Thanks,
Liwei.


> 
> 
> thanks,
> 
> Takashi
> 
> 
> --- a/sound/pci/hda/hda_intel.c
> +++ b/sound/pci/hda/hda_intel.c
> @@ -1788,9 +1788,6 @@ static int azx_first_init(struct azx *chip)
>  			chip->msi = 0;
>  	}
>  
> -	if (azx_acquire_irq(chip, 0) < 0)
> -		return -EBUSY;
> -
>  	pci_set_master(pci);
>  	synchronize_irq(bus->irq);
>  
> @@ -1904,6 +1901,9 @@ static int azx_first_init(struct azx *chip)
>  		return -ENODEV;
>  	}
>  
> +	if (azx_acquire_irq(chip, 0) < 0)
> +		return -EBUSY;
> +
>  	strcpy(card->driver, "HDA-Intel");
>  	strlcpy(card->shortname, driver_short_names[chip->driver_type],
>  		sizeof(card->shortname));
> 
>