kern/51186: pointer arithmatic error in ugen.c

Daan Vreeken [PA4DAN] pa4dan at vitsch.net
Sun Apr 20 07:50:17 PDT 2003


>Number:         51186
>Category:       kern
>Synopsis:       pointer arithmatic error in ugen.c
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Apr 20 07:50:14 PDT 2003
>Closed-Date:
>Last-Modified:
>Originator:     Daan Vreeken [PA4DAN]
>Release:        FreeBSD 5.0
>Organization:
none
>Environment:
System: FreeBSD 5.0 (and all others I checked)


>Description:

I believe there is a pointer arithmatic error in line 965 of ugen.c .
The entire piece of code reads :

961:    /* throw away oldest input if the buffer is full */
962:    if(sce->fill < sce->cur && sce->cur <= sce->fill + count) {
963:            sce->cur += count;
964:            if(sce->cur >= sce->limit)
965:                    sce->cur = sce->ibuf + (sce->limit - sce->cur);
966:            DPRINTFN(5, ("ugen_isoc_rintr: throwing away %d bytes\n",
967:                        count));
978:    }

count gets added to sce->cur .
if the pointer equals/exceeds the end of the buffer, we move it to the
beginnen of the buffer (plus the X bytes it was past the end).

If sce->cur exceeds sce->limit, (sce->cur - sce->limit) would be a negative
value. (resulting in a sce->cur pointer sitting X bytes before the beginning
of the buffer)


>How-To-Repeat:
	n/a

>Fix:

--- ugen.c.diff begins here ---
965c965
< 			sce->cur = sce->ibuf + (sce->limit - sce->cur);
---
> 			sce->cur = sce->ibuf + (sce->cur - sce->limit);
--- ugen.c.diff ends here ---


>Release-Note:
>Audit-Trail:
>Unformatted:


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