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Re: [Qemu-devel] [PATCH] usb-serial: Fix memory overruns with usb serial
From: |
Jason Wessel |
Subject: |
Re: [Qemu-devel] [PATCH] usb-serial: Fix memory overruns with usb serial emulation |
Date: |
Wed, 17 Sep 2008 06:54:47 -0500 |
User-agent: |
Thunderbird 2.0.0.16 (X11/20080724) |
Paul Brook wrote:
> On Wednesday 17 September 2008, Paul Brook wrote:
>
>> On Wednesday 17 September 2008, Jason Wessel wrote:
>>
>>> * Fix a memory overrun
>>> recv_buf[RECV_BUF + 1];
>>> This has to be + 1 because RECV_BUF is used for memcpy computations
>>> in usb_serial_read() such that an extra byte is 0..RECV_BUF bytes
>>> are used.
>>>
>> I think this is wrong. I can't see any way this code could overflow.
>>
>
> On further inspection I can see a bug, but the above change is not the
> correct
> fix, and it will cause lost data not overflows. The calculation of
> first_size is incorrect when the buffer has wrapped.
>
The overflow was a result of the printf()'s introduced to track and
print all the data. So it is correct in that you do not need the
RECV_BUF+1 for the buffer for the base patch. I did not see any kind of
miscalculation with the first_size with or without the wrap condition.
Regression testing with all the checksummed packets shows zero failures
with the revised attached patch.
Obviously the math error as a result of not using variables that are
large enough is a very real problem. With results that can easily be
demonstrated.
Jason.
From: Jason Wessel <address@hidden>
Subject: [PATCH] usb-serial: Fix data corruption with usb serial emulation
* Remove the unused send_buf variable and its constant.
* Fix a math error
The variables recv_ptr and recv_used are not large enough to hold
the constant 384, which causes data corruption when the pointer is
reset with: s->recv_ptr = (s->recv_ptr + len) % RECV_BUF;
Signed-off-by: Jason Wessel <address@hidden>
---
hw/usb-serial.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
--- a/hw/usb-serial.c
+++ b/hw/usb-serial.c
@@ -22,7 +22,6 @@ do { printf("usb-serial: " fmt , ##args)
#endif
#define RECV_BUF 384
-#define SEND_BUF 128 // Not used for now
/* Commands */
#define FTDI_RESET 0
@@ -94,9 +93,8 @@ typedef struct {
uint16_t vendorid;
uint16_t productid;
uint8_t recv_buf[RECV_BUF];
- uint8_t recv_ptr;
- uint8_t recv_used;
- uint8_t send_buf[SEND_BUF];
+ uint16_t recv_ptr;
+ uint16_t recv_used;
uint8_t event_chr;
uint8_t error_chr;
uint8_t event_trigger;