Re: [Qemu-devel] [PATCH 2/4] scsi-generic: avoid out-of-bounds access to VPD page list

[Max Reitz]

On 29.10.18 18:34, Paolo Bonzini wrote:
> A device can report an excessive number of VPD pages when asked for a
> list; this can cause an out-of-bounds access to buf in
> scsi_generic_set_vpd_bl_emulation.  It should not happen, but
> it is technically not incorrect so handle it: do not check any byte
> past the allocation length that was sent to the INQUIRY command.

(Minor note: Since the list must be kept in ascending order, it's fully
correct to only check the first sizeof(buf) - 4 == 0xf6 bytes, because
it actually has to be at index 0xb0 or before, if the device supports it.)

> Reported-by: Max Reitz <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  hw/scsi/scsi-generic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
> index aebb7cdd82..c5497bbea8 100644
> --- a/hw/scsi/scsi-generic.c
> +++ b/hw/scsi/scsi-generic.c
> @@ -538,7 +538,7 @@ static void scsi_generic_set_vpd_bl_emulation(SCSIDevice 
> *s)
>      }
>  
>      page_len = buf[3];

You lost your enthusiasm for fixing the accesses to be proper big-endian
16-bit accesses so quickly? :-)

> -    for (i = 4; i < page_len + 4; i++) {
> +    for (i = 4; i < MIN(sizeof(buf), page_len + 4); i++) {

Reviewed-by: Max Reitz <address@hidden>

>          if (buf[i] == 0xb0) {
>              s->needs_vpd_bl_emulation = false;
>              return;
>

signature.asc
Description: OpenPGP digital signature