Avoid OOB access by verifying the requested address belong to
the actual card size. Return ADDRESS_ERROR when not in range.
Only move the state machine to ReceivingData if there is no
pending error.

  "SD Specifications Part 1 Physical Layer Simplified Spec. v3.01"

  4.3.4 Data Write

  * Block Write

  Write command is rejected if BLOCK_LEN_ERROR or ADDRESS_ERROR
  occurred and no data transfer is performed.

Fixes: CVE-2020-13253
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Buglink: https://bugs.launchpad.net/qemu/+bug/1880822
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
Cc: Prasad J Pandit <pjp@fedoraproject.org>

v2: check for blksz in range, only go to sd_receivingdata_state
    if no error.
---
 hw/sd/sd.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/hw/sd/sd.c b/hw/sd/sd.c
index 3c06a0ac6d..2254dc7acc 100644
--- a/hw/sd/sd.c
+++ b/hw/sd/sd.c
@@ -1211,17 +1211,18 @@ static sd_rsp_type_t sd_normal_command(SDState *sd, SDRequest req)
             /* Writing in SPI mode not implemented.  */
             if (sd->spi)
                 break;
-            sd->state = sd_receivingdata_state;
-            sd->data_start = addr;
-            sd->data_offset = 0;
-            sd->blk_written = 0;
-
-            if (sd->data_start + sd->blk_len > sd->size)
+            if (addr + sd->blk_len >= sd->size) {
                 sd->card_status |= ADDRESS_ERROR;
-            if (sd_wp_addr(sd, sd->data_start))
+            } else if (sd_wp_addr(sd, sd->data_start)) {
                 sd->card_status |= WP_VIOLATION;
-            if (sd->csd[14] & 0x30)
+            } else if (sd->csd[14] & 0x30) {
                 sd->card_status |= WP_VIOLATION;
+            } else {
+                sd->state = sd_receivingdata_state;
+                sd->data_start = addr;
+                sd->data_offset = 0;
+                sd->blk_written = 0;
+            }
             return sd_r1;
 
         default:
-- 
2.21.3

On 6/4/20 8:25 PM, Philippe Mathieu-Daudé wrote:
> Avoid OOB access by verifying the requested address belong to
> the actual card size. Return ADDRESS_ERROR when not in range.
> Only move the state machine to ReceivingData if there is no
> pending error.
> 
>   "SD Specifications Part 1 Physical Layer Simplified Spec. v3.01"
> 
>   4.3.4 Data Write
> 
>   * Block Write
> 
>   Write command is rejected if BLOCK_LEN_ERROR or ADDRESS_ERROR
>   occurred and no data transfer is performed.
> 
> Fixes: CVE-2020-13253
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Buglink: https://bugs.launchpad.net/qemu/+bug/1880822

While the reproducer triggers the OOB via CMD24, other commands have the
same problem, so I'll post a v3.

> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> Cc: Prasad J Pandit <pjp@fedoraproject.org>
> 
> v2: check for blksz in range, only go to sd_receivingdata_state
>     if no error.
> ---
>  hw/sd/sd.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/sd/sd.c b/hw/sd/sd.c
> index 3c06a0ac6d..2254dc7acc 100644
> --- a/hw/sd/sd.c
> +++ b/hw/sd/sd.c
> @@ -1211,17 +1211,18 @@ static sd_rsp_type_t sd_normal_command(SDState *sd, SDRequest req)
>              /* Writing in SPI mode not implemented.  */
>              if (sd->spi)
>                  break;
> -            sd->state = sd_receivingdata_state;
> -            sd->data_start = addr;
> -            sd->data_offset = 0;
> -            sd->blk_written = 0;
> -
> -            if (sd->data_start + sd->blk_len > sd->size)
> +            if (addr + sd->blk_len >= sd->size) {
>                  sd->card_status |= ADDRESS_ERROR;
> -            if (sd_wp_addr(sd, sd->data_start))
> +            } else if (sd_wp_addr(sd, sd->data_start)) {
>                  sd->card_status |= WP_VIOLATION;
> -            if (sd->csd[14] & 0x30)
> +            } else if (sd->csd[14] & 0x30) {
>                  sd->card_status |= WP_VIOLATION;
> +            } else {
> +                sd->state = sd_receivingdata_state;
> +                sd->data_start = addr;
> +                sd->data_offset = 0;
> +                sd->blk_written = 0;
> +            }
>              return sd_r1;
>  
>          default:
>