[Python-Dev] unintentional and unsafe use of realpath()

Mon Sep 12 07:23:53 CEST 2005

Peter Jones wrote:
> Another problem (which I have not fixed) is that when realpath() is
> used, in some cases MAXPATHLEN is smaller than the system's
> PATH_MAX/pathconf(path, _PC_PATH_MAX).

The linux man page for realpath() has this at the bottom:
BUGS
 Never use this function. It is broken by design since it is impossible
 to determine a suitable size for the output buffer. According to POSIX
 a buffer of size PATH_MAX suffices, but PATH_MAX need not be a defined
 constant, and may have to be obtained using pathconf(). And asking
 pathconf() does not really help, since on the one hand POSIX warns that
 the result of pathconf() may be huge and unsuitable for mallocing mem-
 ory. And on the other hand pathconf() may return -1 to signify that
 PATH_MAX is not bounded.
So maybe it shouldn't be using realpath() at all?
-- 
Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	 | A citizen of NewZealandCorp, a	 |
Christchurch, New Zealand	 | wholly-owned subsidiary of USA Inc. |
greg.ewing at canterbury.ac.nz	 +--------------------------------------+