[PATCH v2] hw/sd/sdcard: Verify CMD24 (Block Write) address is valid

[Philippe Mathieu-Daudé]

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