BugTraq
gcc 4.1 bug miscompiles pointer range checks, may place you at risk Apr 17 2006 08:03PM
Felix von Leitner (felix-bugtraq fefe de) (6 replies)
I wrote a small library of functions to do typical range checks as they
are needed in code that handles incoming packets or messages from
untrusted sources. My impetus was SMB code, in case you want to know.

Here is one of my functions:

static inline int range_ptrinbuf(const void* buf,unsigned long len,const void* ptr) {
register const char* c=(const char*)buf; /* no pointer arithmetic on void* */
return (c && c+len>c && (const char*)ptr-c<len);
}

Of course, when developing security critical code like this, you also
write a good test suite for it, that exercises all the cases. Here is
part of my test suite:

assert(range_ptrinbuf(buf,(unsigned long)-1,buf+1)==0);

Imagine my surprise when this assertion failed. I had compiled the
code with gcc 4.1 and compiled it without optimizing (I mention this
because for most gcc bugs, a workaround is disabling the optimizer).

gcc 3 compiles this code correctly. I tested this on x86 and amd64.
I mention this here because "c+len>c" is the code with which you would
typically check for integer overflows, which is a check that for example
an IP stack would do, or Samba. So, if you compiled your kernel with
gcc 4.1, or your Samba, or some other packet handling code in a security
relevant context, you might want to recompile with gcc 3.

Felix

[ reply ]
Re: gcc 4.1 bug miscompiles pointer range checks, may place you at risk Apr 18 2006 07:16PM
Florian Weimer (fw deneb enyo de)
Re: gcc 4.1 bug miscompiles pointer range checks, may place you at risk Apr 18 2006 09:21AM
Gabor Gombas (gombasg sztaki hu)
Re: gcc 4.1 bug miscompiles pointer range checks, may place you at risk Apr 18 2006 07:45AM
Alexander Klimov (alserkli inbox ru)
Re: gcc 4.1 bug miscompiles pointer range checks, may place you at risk Apr 18 2006 12:15AM
Nate Eldredge (nge cs hmc edu)
Re: gcc 4.1 bug miscompiles pointer range checks, may place you at risk Apr 17 2006 11:57PM
Michael Chamberlain (michael chamberlain net au)
Re: gcc 4.1 bug miscompiles pointer range checks, may place you at risk Apr 17 2006 10:26PM
Forrest J. Cavalier III (mibsoft mibsoftware com)


 

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