[Qemu-devel] [PATCH v4] scsi: esp: check length before dma read

[P J P]

From: Prasad J Pandit <address@hidden>

While doing DMA read into ESP command buffer 's->cmdbuf', it could
write past the 's->cmdbuf' area, if it was partially filled;
ie. 's->cmdlen' wasn't set at the start of the buffer.
Check 'len' 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         | 6 ++++--
 include/hw/scsi/esp.h | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

Update as per
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg04269.html

diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
index 4b94bbc..cc74ba8 100644
--- a/hw/scsi/esp.c
+++ b/hw/scsi/esp.c
@@ -249,6 +249,8 @@ static void esp_do_dma(ESPState *s)
     len = s->dma_left;
     if (s->do_cmd) {
         trace_esp_do_dma(s->cmdlen, len);
+        assert (s->cmdlen <= sizeof(s->cmdbuf) &&
+                len <= sizeof(s->cmdbuf) - s->cmdlen);
         s->dma_memory_read(s->dma_opaque, &s->cmdbuf[s->cmdlen], len);
         s->ti_size = 0;
         s->cmdlen = 0;
@@ -348,7 +350,7 @@ 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 +454,7 @@ 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;
 
-- 
2.5.5