Re: [Qemu-devel] [PATCH v3] scsi: esp: check TI buffer index before read/write

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/06/2016 18:34, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> The 53C9X Fast SCSI Controller(FSC) comes with internal 16-byte
> FIFO buffers. One is used to handle commands and other is for
> information transfer. Three control variables 'ti_rptr',
> 'ti_wptr' and 'ti_size' are used to control r/w access to the
> information transfer buffer ti_buf[TI_BUFSZ=16]. In that,
> 
> 'ti_rptr' is used as read index, where read occurs.
> 'ti_wptr' is a write index, where write would occur.
> 'ti_size' indicates total bytes to be read from the buffer.
> 
> While reading/writing to this buffer, index could exceed its
> size. Add check to avoid OOB r/w access.
> 
> Reported-by: Huawei PSIRT <psirt@huawei.com>
> Reported-by: Li Qiang <liqiang6-s@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/scsi/esp.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> Update as per:
>   -> https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg01326.html
> 
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index c2f6f8f..4b94bbc 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -403,19 +403,17 @@ uint64_t esp_reg_read(ESPState *s, uint32_t saddr)
>      trace_esp_mem_readb(saddr, s->rregs[saddr]);
>      switch (saddr) {
>      case ESP_FIFO:
> -        if (s->ti_size > 0) {
> +        if ((s->rregs[ESP_RSTAT] & STAT_PIO_MASK) == 0) {
> +            /* Data out.  */
> +            qemu_log_mask(LOG_UNIMP, "esp: PIO data read not implemented\n");
> +            s->rregs[ESP_FIFO] = 0;
> +            esp_raise_irq(s);
> +        } else if (s->ti_rptr < s->ti_wptr) {
>              s->ti_size--;
> -            if ((s->rregs[ESP_RSTAT] & STAT_PIO_MASK) == 0) {
> -                /* Data out.  */
> -                qemu_log_mask(LOG_UNIMP,
> -                              "esp: PIO data read not implemented\n");
> -                s->rregs[ESP_FIFO] = 0;
> -            } else {
> -                s->rregs[ESP_FIFO] = s->ti_buf[s->ti_rptr++];
> -            }
> +            s->rregs[ESP_FIFO] = s->ti_buf[s->ti_rptr++];
>              esp_raise_irq(s);
>          }
> -        if (s->ti_size == 0) {
> +        if (s->ti_rptr == s->ti_wptr) {
>              s->ti_rptr = 0;
>              s->ti_wptr = 0;
>          }
> @@ -459,7 +457,7 @@ void esp_reg_write(ESPState *s, uint32_t saddr, uint64_t val)
>              } else {
>                  trace_esp_error_fifo_overrun();
>              }
> -        } else if (s->ti_size == TI_BUFSZ - 1) {
> +        } else if (s->ti_wptr == TI_BUFSZ - 1) {
>              trace_esp_error_fifo_overrun();
>          } else {
>              s->ti_size++;
> 

Queued, thanks.

Paolo