Re: [Qemu-devel] [PATCH v3] scsi: esp: check length before dma read

[Paolo Bonzini]

On 15/06/2016 18:16, P J P wrote:
> From: Prasad J Pandit <address@hidden>
> 
> While doing DMA read into ESP command buffer 's->cmdbuf', the
> length parameter could exceed the buffer size. Add check to avoid
> OOB access. Also increase the command buffer size to 32, which
> is maximum when 's->do_cmd' is set.
> 
> Reported-by: Li Qiang <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
>  hw/scsi/esp.c         | 7 +++++--
>  include/hw/scsi/esp.h | 3 ++-
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> Update as per
>   -> https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg04194.html

It's okay, but...

> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index 4b94bbc..1208a63 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -249,6 +249,9 @@ static void esp_do_dma(ESPState *s)
>      len = s->dma_left;
>      if (s->do_cmd) {
>          trace_esp_do_dma(s->cmdlen, len);
> +        if (len > sizeof(s->cmdbuf) - s->cmdlen) {
> +            return;
> +        }

... this is not necessary so it can be replaced by an assertion.  I can
do that when applying.

Paolo

>          s->dma_memory_read(s->dma_opaque, &s->cmdbuf[s->cmdlen], len);
>          s->ti_size = 0;
>          s->cmdlen = 0;
> @@ -348,7 +351,7 @@ static void handle_ti(ESPState *s)
>      s->dma_counter = dmalen;
>  
>      if (s->do_cmd)
> -        minlen = (dmalen < 32) ? dmalen : 32;
> +        minlen = (dmalen < ESP_CMDBUF_SZ) ? dmalen : ESP_CMDBUF_SZ;
>      else if (s->ti_size < 0)
>          minlen = (dmalen < -s->ti_size) ? dmalen : -s->ti_size;
>      else
> @@ -452,7 +455,7 @@ void esp_reg_write(ESPState *s, uint32_t saddr, uint64_t 
> val)
>          break;
>      case ESP_FIFO:
>          if (s->do_cmd) {
> -            if (s->cmdlen < TI_BUFSZ) {
> +            if (s->cmdlen < ESP_CMDBUF_SZ) {
>                  s->cmdbuf[s->cmdlen++] = val & 0xff;
>              } else {
>                  trace_esp_error_fifo_overrun();
> diff --git a/include/hw/scsi/esp.h b/include/hw/scsi/esp.h
> index 6c79527..d2c4886 100644
> --- a/include/hw/scsi/esp.h
> +++ b/include/hw/scsi/esp.h
> @@ -14,6 +14,7 @@ void esp_init(hwaddr espaddr, int it_shift,
>  
>  #define ESP_REGS 16
>  #define TI_BUFSZ 16
> +#define ESP_CMDBUF_SZ 32
>  
>  typedef struct ESPState ESPState;
>  
> @@ -31,7 +32,7 @@ struct ESPState {
>      SCSIBus bus;
>      SCSIDevice *current_dev;
>      SCSIRequest *current_req;
> -    uint8_t cmdbuf[TI_BUFSZ];
> +    uint8_t cmdbuf[ESP_CMDBUF_SZ];
>      uint32_t cmdlen;
>      uint32_t do_cmd;
>  
>