Re: [BUG] ALSA: korg1212: Potential NULL pointer dereference in snd_korg1212_interrupt()

[Takashi Iwai]

On Fri, 07 May 2021 11:18:56 +0200,
Подгорный Алексей Олегович wrote:
> 
> snd_korg1212_create() makes the following steps during initialization
> of the card:
> 1) registers an interrupt handler (lines 2230-2232)
> 2) allocates and initializes korg1212->sharedBufferPtr (lines 2280-2287)
> 3) reboots the card via snd_korg1212_Send1212Command() (line 2358)
> 
> 2145    static int snd_korg1212_create(struct snd_card *card, struct
>                                  pci_dev *pci, struct snd_korg1212 **rchip)
> 2147    {
>                 ...
> 2230            err = request_irq(pci->irq, snd_korg1212_interrupt,
> 2231                                        IRQF_SHARED,
> 2232                                        KBUILD_MODNAME, korg1212);
>                 ...
> 2280            if (snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV, &pci->dev,
> 2281            sizeof(struct KorgSharedBuffer), &korg1212->dma_shared) < 0){
> 
> 2282                         snd_printk(KERN_ERR "korg1212: can not
>                                  allocate shared buffer memory (%zdbytes)\n",
>                                  sizeof(struct KorgSharedBuffer));
> 
> 2283                         snd_korg1212_free(korg1212);
> 2284                         return -ENOMEM;
> 2285            }
> 2286            korg1212->sharedBufferPtr =
>                         (struct KorgSharedBuffer*)korg1212->dma_shared.area;
> 2287            korg1212->sharedBufferPhy = korg1212->dma_shared.addr;
>                 ...
> 2358            rc = snd_korg1212_Send1212Command(korg1212,
>                         K1212_DB_RebootCard, 0, 0, 0, 0);
>                 ...
> 2412    }
> 
> But if interrupt happens when snd_korg1212_create() is still within
> lines 2233-2286,
> snd_korg1212_interrupt() may dereference korg1212->sharedBufferPtr before
> it was initialized without any checks (line 1149):
> 
> 1098    static irqreturn_t snd_korg1212_interrupt(int irq, void *dev_id)
> 1099    {
>                 ...
> 1116            switch (doorbellValue) {
>                 ...
> 1145                        case K1212_DB_CARDSTOPPED:
> 1146                            K1212_DEBUG_PRINTK_VERBOSE("K1212_DEBUG: IRQ
>                                         CSTP count - %ld, %x, [%s].\n",
> 1147                                korg1212->irqcount, doorbellValue,
> 1148                                stateName[korg1212->cardState]);
> 1149                        korg1212->sharedBufferPtr->cardCommand = 0;
>                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 1150                        break;
>                 ...
> 1185    }
> 
> Should we be sure that such interrupt cannot happen or
> should we move the registration of the interrupt handler after
> korg1212->sharedBufferPtr is initialized?

Yes, in general the IRQ handler should be registered at the end.
Could you submit a fix patch?


thanks,

Takashi