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

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

[P J P]

From: Prasad J Pandit <pjp@fedoraproject.org>

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 <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 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

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;
+        }
         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;
 
-- 
2.5.5

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 <pjp@fedoraproject.org>
> 
> 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 <liqiang6-s@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  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;
>  
> 

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 <pjp@fedoraproject.org>
> 
> 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.

Actually, the commit message is wrong.  The length parameter cannot
exceed the buffer size anymore.  Can you do a v4 with the corrected
commit message and an assert that avoids overflows like in Laszlo's
proposal?  I think this:

   assert (s->cmdlen <= sizeof(s->cmdbuf) &&
           len <= sizeof(s->cmdbuf) - s->cmdlen);

would do.

Thanks,

Paolo

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

[P J P]

  Hello Paolo,

+-- On Wed, 15 Jun 2016, Paolo Bonzini wrote --+
| Actually, the commit message is wrong.  The length parameter cannot
| exceed the buffer size anymore.

  It wouldn't exceed after this patch, right? Is it possible 'esp_do_dma' is 
called via 'esp_transfer_data' with 's->do_cmd' set? 'len' isn't checked 
there.

| Can you do a v4 with the corrected
| commit message and an assert that avoids overflows like in Laszlo's
| proposal?  I think this:
| 
|    assert (s->cmdlen <= sizeof(s->cmdbuf) &&
|            len <= sizeof(s->cmdbuf) - s->cmdlen);

  Okay.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F

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

[Paolo Bonzini]

On 15/06/2016 19:18, P J P wrote:
>   Hello Paolo,
> 
> +-- On Wed, 15 Jun 2016, Paolo Bonzini wrote --+
> | Actually, the commit message is wrong.  The length parameter cannot
> | exceed the buffer size anymore.
> 
>   It wouldn't exceed after this patch, right? Is it possible 'esp_do_dma' is 
> called via 'esp_transfer_data' with 's->do_cmd' set? 'len' isn't checked 
> there.

No, it's not possible; see the discussion in reply to v1.

Paolo