Bug 922028

+++ This bug was initially created as a clone of Bug #921950 +++

Guido Vranken reported that regular expressions (regex) originally written by Henry Spencer contains a heap overflow vulnerability.

CWE-122: Heap-based Buffer Overflow

https://guidovranken.wordpress.com/2015/02/04/full-disclosure-heap-overflow-in-h-spencers-regex-library-on-32-bit-systems/
http://www.kb.cert.org/vuls/id/695940

The variable len that holds the length of a regular expression string is "enlarged to such an extent that, in the process of enlarging (multiplication and addition), causes the 32 bit register/variable to overflow." It may be possible for an attacker to use this overflow to change data in memory.

Vulnerable function:
> int /* 0 success, otherwise REG_something */
> regcomp(preg, pattern, cflags)
> regex_t *preg;
> const char *pattern;
> int cflags;
> {

Vulnerable code:
> len = strlen((char *)pattern);
> [...]
> p->ssize = len/(size_t)2*(size_t)3 + (size_t)1; /* ugh */
> p->strip = (sop *)malloc(p->ssize * sizeof(sop));

32-bit systems are affected. It is highly unlikely that 64-bit operating systems would allow such an overflow. (Read: not impossible.)

The library is known to be contained in many different upstream source projects. The code may not be active or used on our platform, e.g. only be used as fallback code.


xen seems to package affected code. Found in:

./xen/stubdom.tar.bz2.contents/stubdom/newlib-1.16.0.tar.gz.contents/newlib-1.16.0/newlib/libc/sys/linux/stdlib/regcomp.c

int				/* 0 success, otherwise REG_something */
regcomp(preg, pattern, cflags)
regex_t *preg;
const char *pattern;
int cflags;
{
[...]
	p->ssize = len/(size_t)2*(size_t)3 + (size_t)1;	/* ugh */
	p->strip = (sop *)malloc(p->ssize * sizeof(sop));

Can you please check if the code lib is used?