On Wed, 7 Apr 2021 at 21:02, Mark Cave-Ayland
<mark.cave-ayl...@ilande.co.uk> wrote:
>
> The const pointer returned by fifo8_pop_buf() lies directly within the array
> used
> to model the FIFO. Building with address sanitizers enabled shows that if the
> caller expects a minimum number of bytes present then if the FIFO is nearly
> full,
> the caller may unexpectedly access past the end of the array.
>
> Introduce esp_fifo_pop_buf() which takes a destination buffer and performs a
> memcpy() in it to guarantee that the caller cannot overwrite the FIFO array
> and
> update all callers to use it. Similarly add underflow protection similar to
> esp_fifo_push() and esp_fifo_pop() so that instead of triggering an assert()
> the operation becomes a no-op.
>
> Buglink: https://bugs.launchpad.net/qemu/+bug/1909247
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
> Tested-by: Alexander Bulekov <alx...@bu.edu>
> ---
> hw/scsi/esp.c | 40 ++++++++++++++++++++++++++++------------
> 1 file changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index ff8fa73de9..1aa2caf57d 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -117,6 +117,23 @@ static uint8_t esp_fifo_pop(Fifo8 *fifo)
> return fifo8_pop(fifo);
> }
>
> +static uint32_t esp_fifo_pop_buf(Fifo8 *fifo, uint8_t *dest, int maxlen)
> +{
> + const uint8_t *buf;
> + uint32_t n;
> +
> + if (maxlen == 0) {
> + return 0;
> + }
> +
> + buf = fifo8_pop_buf(fifo, maxlen, &n);
> + if (dest) {
> + memcpy(dest, buf, n);
> + }
> +
> + return n;
> +}
> +
> static uint32_t esp_get_tc(ESPState *s)
> {
> uint32_t dmalen;
> @@ -241,11 +258,11 @@ static uint32_t get_cmd(ESPState *s, uint32_t maxlen)
> if (dmalen == 0) {
> return 0;
> }
> - memcpy(buf, fifo8_pop_buf(&s->fifo, dmalen, &n), dmalen);
> - if (dmalen >= 3) {
> + n = esp_fifo_pop_buf(&s->fifo, buf, dmalen);
> + if (n >= 3) {
> buf[0] = buf[2] >> 5;
> }
> - fifo8_push_all(&s->cmdfifo, buf, dmalen);
> + fifo8_push_all(&s->cmdfifo, buf, n);
> }
> trace_esp_get_cmd(dmalen, target);
This bit could be tidied up further -- it currently sets
dmalen = MIN(fifo8_num_used(&s->fifo), maxlen);
in order not to pull more bytes out of the FIFO than it has in it;
but now we are making that check in esp_fifo_pop_buf() I think you
could just do
dmalen = esp_fifo_pop_buf(&s->fifo, buf, maxlen);
and drop the
dmalen = MIN(fifo8_num_used(&s->fifo), maxlen);
if (dmalen == 0) {
return 0;
}
part and the use of 'n' entirely.
But this code isn't wrong, so we can do that later to avoid having
to respin here.
Reviewed-by: Peter Maydell <peter.mayd...@linaro.org>
thanks
-- PMM
