Re: [PATCH] hw/scsi/scsi-disk: MODE_PAGE_ALLS not allowed in MODE SELECT commands

[Philippe Mathieu-Daudé]

On 11/5/21 12:37, Mauro Matteo Cascella wrote:
> MODE_PAGE_ALLS causes an off-by-one error in mode_sense_page() when accessing
> the stack-allocated mode_sense_valid buffer. MODE_PAGE_ALLS is only valid for
> MODE SENSE commands. Do not process it in MODE SELECT commands.
> 

Cc: qemu-stable@nongnu.org

> Fixes: CVE-2021-3930
> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2020588
> Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
> Reported-by: Qiuhao Li <qiuhao.li@outlook.com>

See also:
https://lore.kernel.org/qemu-devel/20210204225041.1822673-1-philmd@redhat.com/

> ---
>  hw/scsi/scsi-disk.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
> index e8a547dbb7..5852e8dcfd 100644
> --- a/hw/scsi/scsi-disk.c
> +++ b/hw/scsi/scsi-disk.c
> @@ -1087,6 +1087,7 @@ static int mode_sense_page(SCSIDiskState *s, int page, 
> uint8_t **p_outbuf,
>      uint8_t *p = *p_outbuf + 2;
>      int length;
>  
> +    assert(page != MODE_PAGE_ALLS);
>      if ((mode_sense_valid[page] & (1 << s->qdev.type)) == 0) {
>          return -1;
>      }
> @@ -1428,6 +1429,11 @@ static int scsi_disk_check_mode_select(SCSIDiskState 
> *s, int page,
>          return -1;
>      }
>  
> +    /* MODE_PAGE_ALLS is only valid for MODE SENSE commands */
> +    if (page == MODE_PAGE_ALLS) {
> +        return -1;
> +    }
> +
>      p = mode_current;
>      memset(mode_current, 0, inlen + 2);
>      len = mode_sense_page(s, page, &p, 0);
>