XI2's copyRawEvent() question

[Roger Cruz]

BTW, changing the code to use "len" rather than the sizeof() fixed my crash.

diff ../../libXi-1.3-orig/src/XExtInt.c src/XExtInt.c
1196c1196
<     ptr = cookie_out->data = malloc(sizeof(XIRawEvent));
---
>     ptr = cookie_out->data = malloc(len);


-----Original Message-----
From: xorg-bounces+roger.cruz=virtualcomputer.com at lists.freedesktop.org on behalf of Roger Cruz
Sent: Mon 4/25/2011 3:35 PM
To: xorg at lists.freedesktop.org
Subject: XI2's copyRawEvent() question
 

In trying to understand a heap corruption when I added XI2 RawMotion event handling to our Xinput-based application, I came across the following routine copyRawEvent() in libxi-1.3/src/XExtInt.c.  My question is what is the purpose of computing "len" if it is not used?  Should it have been used as an argument to malloc(). 

copyRawEvent(XGenericEventCookie *cookie_in,
             XGenericEventCookie *cookie_out)
{
    XIRawEvent *in, *out;
    void *ptr;
    int len;
    int bits;

    in = cookie_in->data;

    bits = count_bits(in->valuators.mask, in->valuators.mask_len);
    len = sizeof(XIRawEvent) + in->valuators.mask_len;
    len += bits * sizeof(double) * 2;

    ptr = cookie_out->data = malloc(sizeof(XIRawEvent));
    if (!ptr)
        return False;

    out = next_block(&ptr, sizeof(XIRawEvent));
    *out = *in;
    out->valuators.mask = next_block(&ptr, out->valuators.mask_len);
    memcpy(out->valuators.mask, in->valuators.mask, out->valuators.mask_len);

    out->valuators.values = next_block(&ptr, bits * sizeof(double));
    memcpy(out->valuators.values, in->valuators.values, bits * sizeof(double));

    out->raw_values = next_block(&ptr, bits * sizeof(double));
    memcpy(out->raw_values, in->raw_values, bits * sizeof(double));

    return True;
}

When I use valgrind, I get the following output as the culprit for the crash

==4166== Invalid write of size 1
==4166==    at 0x4C29F04: memcpy (mc_replace_strmem.c:497)
==4166==    by 0x8F39180: ??? (in /usr/lib/libXi.so.6.1.0)
==4166==    by 0x7433D48: _XCopyEventCookie (in /usr/lib/libX11.so.6.3.0)
==4166==    by 0x7425166: XPeekEvent (in /usr/lib/libX11.so.6.3.0)
==4166==    by 0x49C3E3: process_key (x11_be.c:1065)
==4166==    by 0x49EA5C: event_key_release (x11_be.c:2201)
==4166==    by 0x49DD6E: x11_be_process_events (x11_be.c:1892)
==4166==    by 0x4A38F4: x11_be_main_loop (x11_be.c:4353)
==4166==    by 0x4A39E1: x11_be_thread_main (x11_be.c:4385)
==4166==    by 0x87549C9: start_thread (pthread_create.c:300)
==4166==    by 0x8A516FC: clone (clone.S:112)
==4166==  Address 0x168afe80 is 0 bytes after a block of size 96 alloc'd
==4166==    at 0x4C284A8: malloc (vg_replace_malloc.c:236)
==4166==    by 0x8F390BD: ??? (in /usr/lib/libXi.so.6.1.0)
==4166==    by 0x7433D48: _XCopyEventCookie (in /usr/lib/libX11.so.6.3.0)
==4166==    by 0x7425166: XPeekEvent (in /usr/lib/libX11.so.6.3.0)
==4166==    by 0x49C3E3: process_key (x11_be.c:1065)
==4166==    by 0x49EA5C: event_key_release (x11_be.c:2201)
==4166==    by 0x49DD6E: x11_be_process_events (x11_be.c:1892)
==4166==    by 0x4A38F4: x11_be_main_loop (x11_be.c:4353)
==4166==    by 0x4A39E1: x11_be_thread_main (x11_be.c:4385)
==4166==    by 0x87549C9: start_thread (pthread_create.c:300)

Thanks in advance,

Roger R. Cruz 

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