Re: [Qemu-devel] [PATCH v2] ps2: check PS2Queue indices in post_load routine

[Paolo Bonzini]

On 16/11/2017 11:16, P J P wrote:
> From: Prasad J Pandit <address@hidden>
> 
> During Qemu guest migration, a destination process invokes ps2
> post_load function. In that, if 'rptr' and 'count' values were
> invalid, it could lead to OOB access issue. Add check to avoid
> it.
> 
> Reported-by: Cyrille Chatras <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
>  hw/input/ps2.c | 39 ++++++++++++++++++---------------------
>  1 file changed, 18 insertions(+), 21 deletions(-)
> 
> Update: return -1(bad indices) error, instead of correcting values
>   -> https://lists.gnu.org/archive/html/qemu-devel/2017-11/msg02964.html
> 
> diff --git a/hw/input/ps2.c b/hw/input/ps2.c
> index f388a23c8e..35392d55fc 100644
> --- a/hw/input/ps2.c
> +++ b/hw/input/ps2.c
> @@ -1222,32 +1222,37 @@ static void ps2_common_reset(PS2State *s)
>      s->update_irq(s->update_arg, 0);
>  }
>  
> -static void ps2_common_post_load(PS2State *s)
> +static int ps2_common_post_load(PS2State *s)
>  {
>      PS2Queue *q = &s->queue;
>      int size;
>      int i;
>      int tmp_data[PS2_QUEUE_SIZE];
>  
> +    if (q->count < 0 || q->rptr < 0 || q->rptr >= sizeof(q->data)) {
> +        return -1;
> +    }
> +
>      /* set the useful data buffer queue size, < PS2_QUEUE_SIZE */
>      size = q->count > PS2_QUEUE_SIZE ? 0 : q->count;
>  
>      /* move the queue elements to the start of data array */
> -    if (size > 0) {
> -        for (i = 0; i < size; i++) {
> -            /* move the queue elements to the temporary buffer */
> -            tmp_data[i] = q->data[q->rptr];
> -            if (++q->rptr == 256) {
> -                q->rptr = 0;
> -            }
> +    for (i = 0; i < size; i++) {
> +        /* move the queue elements to the temporary buffer */
> +        tmp_data[i] = q->data[q->rptr];
> +        if (++q->rptr == 256) {
> +            q->rptr = 0;
>          }
> -        memcpy(q->data, tmp_data, size);
>      }
> +    memcpy(q->data, tmp_data, size);
> +
>      /* reset rptr/wptr/count */
>      q->rptr = 0;
>      q->wptr = size;
>      q->count = size;
>      s->update_irq(s->update_arg, q->count != 0);
> +
> +    return 0;
>  }
>  
>  static void ps2_kbd_reset(void *opaque)
> @@ -1346,9 +1351,7 @@ static int ps2_kbd_post_load(void* opaque, int 
> version_id)
>      if (version_id == 2)
>          s->scancode_set=2;
>  
> -    ps2_common_post_load(ps2);
> -
> -    return 0;
> +    return ps2_common_post_load(ps2);
>  }
>  
>  static int ps2_kbd_pre_save(void *opaque)
> @@ -1356,9 +1359,7 @@ static int ps2_kbd_pre_save(void *opaque)
>      PS2KbdState *s = (PS2KbdState *)opaque;
>      PS2State *ps2 = &s->common;
>  
> -    ps2_common_post_load(ps2);
> -
> -    return 0;
> +    return ps2_common_post_load(ps2);
>  }
>  
>  static const VMStateDescription vmstate_ps2_keyboard = {
> @@ -1386,9 +1387,7 @@ static int ps2_mouse_post_load(void *opaque, int 
> version_id)
>      PS2MouseState *s = (PS2MouseState *)opaque;
>      PS2State *ps2 = &s->common;
>  
> -    ps2_common_post_load(ps2);
> -
> -    return 0;
> +    return ps2_common_post_load(ps2);
>  }
>  
>  static int ps2_mouse_pre_save(void *opaque)
> @@ -1396,9 +1395,7 @@ static int ps2_mouse_pre_save(void *opaque)
>      PS2MouseState *s = (PS2MouseState *)opaque;
>      PS2State *ps2 = &s->common;
>  
> -    ps2_common_post_load(ps2);
> -
> -    return 0;
> +    return ps2_common_post_load(ps2);
>  }
>  
>  static const VMStateDescription vmstate_ps2_mouse = {
> 

Reviewed-by: Paolo Bonzini <address@hidden>