Re: [Qemu-devel] [PATCH v2] hw/sd: fix out-of-bounds check for multi block reads

[Alistair Francis]

On Mon, Sep 25, 2017 at 12:27 PM, Peter Maydell
<address@hidden> wrote:
> On 20 September 2017 at 07:19, Michael Olbrich <address@hidden> wrote:
>> On Tue, Sep 19, 2017 at 05:09:51PM -0700, Alistair Francis wrote:
>>> On Tue, Sep 19, 2017 at 1:23 AM, Michael Olbrich
>>> <address@hidden> wrote:
>>> > On Mon, Sep 18, 2017 at 02:28:26PM -0700, Alistair Francis wrote:
>>> >> On Sat, Sep 16, 2017 at 3:35 AM, Michael Olbrich
>>> >> <address@hidden> wrote:
>>> >> >  hw/sd/sd.c | 12 ++++++------
>>> >> >  1 file changed, 6 insertions(+), 6 deletions(-)
>>> >> >
>>> >> > diff --git a/hw/sd/sd.c b/hw/sd/sd.c
>>> >> > index ba47bff4db80..35347a5bbcde 100644
>>> >> > --- a/hw/sd/sd.c
>>> >> > +++ b/hw/sd/sd.c
>>> >> > @@ -1797,8 +1797,13 @@ uint8_t sd_read_data(SDState *sd)
>>> >> >          break;
>>> >> >
>>> >> >      case 18:   /* CMD18:  READ_MULTIPLE_BLOCK */
>>> >> > -        if (sd->data_offset == 0)
>>> >> > +        if (sd->data_offset == 0) {
>>> >> > +            if (sd->data_start + io_len > sd->size) {
>>> >> > +                sd->card_status |= ADDRESS_ERROR;
>>> >> > +                return 0x00;
>>> >> > +            }
>>> >>
>>> >> Why move it inside the if (sd->data_offset == 0) and not just below
>>> >> the ret = sd->data[sd->data_offset ++] ?
>>> >>
>>> >> >              BLK_READ_BLOCK(sd->data_start, io_len);
>>> >
>>> > Mostly because of the line above. This copies the full block from the
>>> > backend storage to sd->data, so we need to make sure that the data is
>>> > actually available to fill sd->data, not if it's ok to access a certain
>>> > byte within sd->data.
>>>
>>> Doesn't this mean that the check is only done for the first block
>>> then? When data_offset is 0.
>>
>> No, data_offset is reset at the end of the block.
>> [...]
>
> Alistair, were you planning to provide a reviewed-by: for this
> patch (or did you have more review comments on it)?

Ah woops, this slipped through. Looks fine to me then.

Reviewed-by: Alistair Francis <address@hidden>

Thanks,
Alistair

>
> thanks
> -- PMM