[Qemu-devel] [PATCH] segfault due to buffer overrun in usb-serial

[Qemu-devel] [PATCH] segfault due to buffer overrun in usb-serial

[David S. Ahern]

This fixes a segfault due to buffer overrun in the usb-serial device.
The memcpy was incrementing the start location by recv_used yet, the
computation of first_size (how much to write at the end of the buffer
before wrapping to the front) was not accounting for it. This causes the
next element after the receive buffer (recv_ptr) to get overwritten with
random data.

Signed-off-by: David Ahern <daahern@cisco.com>

diff --git a/hw/usb-serial.c b/hw/usb-serial.c
index 37293ea..c3f3401 100644
--- a/hw/usb-serial.c
+++ b/hw/usb-serial.c
@@ -497,12 +497,28 @@ static int usb_serial_can_read(void *opaque)
 static void usb_serial_read(void *opaque, const uint8_t *buf, int size)
 {
     USBSerialState *s = opaque;
-    int first_size = RECV_BUF - s->recv_ptr;
-    if (first_size > size)
-        first_size = size;
-    memcpy(s->recv_buf + s->recv_ptr + s->recv_used, buf, first_size);
-    if (size > first_size)
-        memcpy(s->recv_buf, buf + first_size, size - first_size);
+    int first_size, start;
+
+    /* room in the buffer? */
+    if (size > (RECV_BUF - s->recv_used))
+        size = RECV_BUF - s->recv_used;
+
+    start = s->recv_ptr + s->recv_used;
+    if (start < RECV_BUF) {
+        /* copy data to end of buffer */
+        first_size = RECV_BUF - start;
+        if (first_size > size)
+            first_size = size;
+
+        memcpy(s->recv_buf + start, buf, first_size);
+
+        /* wrap around to front if needed */
+        if (size > first_size)
+            memcpy(s->recv_buf, buf + first_size, size - first_size);
+    } else {
+        start -= RECV_BUF;
+        memcpy(s->recv_buf + start, buf, size);
+    }
     s->recv_used += size;
 }

[Qemu-devel] Re: [PATCH] segfault due to buffer overrun in usb-serial

[David S. Ahern]

I have not seen response to this. If there are no objections please apply.

Thanks,

David Ahern


On 02/03/2010 09:00 AM, David S. Ahern wrote:
> This fixes a segfault due to buffer overrun in the usb-serial device.
> The memcpy was incrementing the start location by recv_used yet, the
> computation of first_size (how much to write at the end of the buffer
> before wrapping to the front) was not accounting for it. This causes the
> next element after the receive buffer (recv_ptr) to get overwritten with
> random data.
> 
> Signed-off-by: David Ahern <daahern@cisco.com>
> 
> diff --git a/hw/usb-serial.c b/hw/usb-serial.c
> index 37293ea..c3f3401 100644
> --- a/hw/usb-serial.c
> +++ b/hw/usb-serial.c
> @@ -497,12 +497,28 @@ static int usb_serial_can_read(void *opaque)
>  static void usb_serial_read(void *opaque, const uint8_t *buf, int size)
>  {
>      USBSerialState *s = opaque;
> -    int first_size = RECV_BUF - s->recv_ptr;
> -    if (first_size > size)
> -        first_size = size;
> -    memcpy(s->recv_buf + s->recv_ptr + s->recv_used, buf, first_size);
> -    if (size > first_size)
> -        memcpy(s->recv_buf, buf + first_size, size - first_size);
> +    int first_size, start;
> +
> +    /* room in the buffer? */
> +    if (size > (RECV_BUF - s->recv_used))
> +        size = RECV_BUF - s->recv_used;
> +
> +    start = s->recv_ptr + s->recv_used;
> +    if (start < RECV_BUF) {
> +        /* copy data to end of buffer */
> +        first_size = RECV_BUF - start;
> +        if (first_size > size)
> +            first_size = size;
> +
> +        memcpy(s->recv_buf + start, buf, first_size);
> +
> +        /* wrap around to front if needed */
> +        if (size > first_size)
> +            memcpy(s->recv_buf, buf + first_size, size - first_size);
> +    } else {
> +        start -= RECV_BUF;
> +        memcpy(s->recv_buf + start, buf, size);
> +    }
>      s->recv_used += size;
>  }
> 
> 
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Re: [Qemu-devel] [PATCH] segfault due to buffer overrun in usb-serial

[Anthony Liguori]

On 02/03/2010 10:00 AM, David S. Ahern wrote:
> This fixes a segfault due to buffer overrun in the usb-serial device.
> The memcpy was incrementing the start location by recv_used yet, the
> computation of first_size (how much to write at the end of the buffer
> before wrapping to the front) was not accounting for it. This causes the
> next element after the receive buffer (recv_ptr) to get overwritten with
> random data.
>
> Signed-off-by: David Ahern<daahern@cisco.com>
>    

Applied.  Thanks.

Regards,

Anthony Liguori
> diff --git a/hw/usb-serial.c b/hw/usb-serial.c
> index 37293ea..c3f3401 100644
> --- a/hw/usb-serial.c
> +++ b/hw/usb-serial.c
> @@ -497,12 +497,28 @@ static int usb_serial_can_read(void *opaque)
>   static void usb_serial_read(void *opaque, const uint8_t *buf, int size)
>   {
>       USBSerialState *s = opaque;
> -    int first_size = RECV_BUF - s->recv_ptr;
> -    if (first_size>  size)
> -        first_size = size;
> -    memcpy(s->recv_buf + s->recv_ptr + s->recv_used, buf, first_size);
> -    if (size>  first_size)
> -        memcpy(s->recv_buf, buf + first_size, size - first_size);
> +    int first_size, start;
> +
> +    /* room in the buffer? */
> +    if (size>  (RECV_BUF - s->recv_used))
> +        size = RECV_BUF - s->recv_used;
> +
> +    start = s->recv_ptr + s->recv_used;
> +    if (start<  RECV_BUF) {
> +        /* copy data to end of buffer */
> +        first_size = RECV_BUF - start;
> +        if (first_size>  size)
> +            first_size = size;
> +
> +        memcpy(s->recv_buf + start, buf, first_size);
> +
> +        /* wrap around to front if needed */
> +        if (size>  first_size)
> +            memcpy(s->recv_buf, buf + first_size, size - first_size);
> +    } else {
> +        start -= RECV_BUF;
> +        memcpy(s->recv_buf + start, buf, size);
> +    }
>       s->recv_used += size;
>   }
>
>
>
>
>
>