Re: [PATCH] mmc: davinci: avoid NULL deref of host->data in IRQ handler

[Bartosz Golaszewski]

On Wed, 6 May 2026 21:05:37 +0200, Stepan Ionichev <sozdayvek@xxxxxxxxx> said:
> mmc_davinci_irq() returns early only when both host->cmd and
> host->data are NULL:
>
>   if (host->cmd == NULL && host->data == NULL) {
>           ...
>           return IRQ_NONE;
>   }
>
> So we may legitimately reach the rest of the handler with
> host->data == NULL (and therefore data == NULL). The DATDNE branch
> already guards against this with an explicit "if (data != NULL)"
> check, but the subsequent TOUTRD ("read data timeout") and
> CRCWR/CRCRD ("data CRC error") branches dereference data
> unconditionally:
>
>   if (qstatus & MMCST0_TOUTRD) {
>           data->error = -ETIMEDOUT;        <-- NULL deref
>           ...
>           davinci_abort_data(host, data);
>   }
>
>   if (qstatus & (MMCST0_CRCWR | MMCST0_CRCRD)) {
>           data->error = -EILSEQ;           <-- NULL deref
>           ...
>   }
>
> If either bit is set in qstatus while host->data is NULL, the kernel
> will crash inside the IRQ handler. smatch flags this:
>
>   drivers/mmc/host/davinci_mmc.c:933 mmc_davinci_irq() error: we
>     previously assumed 'data' could be null (see line 914)
>
> Gate both branches on a non-NULL data, matching the existing pattern
> used by the DATDNE branch.
>
> No functional change for callers where data is non-NULL, which is
> the only case in which these branches did meaningful work before
> this change.
>
> Signed-off-by: Stepan Ionichev <sozdayvek@xxxxxxxxx>
> ---
>  drivers/mmc/host/davinci_mmc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/davinci_mmc.c b/drivers/mmc/host/davinci_mmc.c
> index 42b0118a4..42ad87aa4 100644
> --- a/drivers/mmc/host/davinci_mmc.c
> +++ b/drivers/mmc/host/davinci_mmc.c
> @@ -928,7 +928,7 @@ static irqreturn_t mmc_davinci_irq(int irq, void *dev_id)
>  		}
>  	}
>
> -	if (qstatus & MMCST0_TOUTRD) {
> +	if (data && (qstatus & MMCST0_TOUTRD)) {
>  		/* Read data timeout */
>  		data->error = -ETIMEDOUT;
>  		end_transfer = 1;
> @@ -940,7 +940,7 @@ static irqreturn_t mmc_davinci_irq(int irq, void *dev_id)
>  		davinci_abort_data(host, data);
>  	}
>
> -	if (qstatus & (MMCST0_CRCWR | MMCST0_CRCRD)) {
> +	if (data && (qstatus & (MMCST0_CRCWR | MMCST0_CRCRD))) {
>  		/* Data CRC error */
>  		data->error = -EILSEQ;
>  		end_transfer = 1;
> --
> 2.43.0
>
>

Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>