dirname/basename leaks in FreeBSD 5.x

iralee3c@gmail.com · *nix forums beginner Joined: 07 Feb 2005 Posts: 1

Based on the documentation and older 4.x implementations, libc versions
of dirname and basename make use of static buffer as such.

static char bname[MAXPATHLEN];

The man page describes this:

ERRORS
The following error codes may be set in errno:

[ENAMETOOLONG] The path component to be returned was larger
than
MAXPATHLEN.

WARNINGS
The dirname() function returns a pointer to internal static
storage space
that will be overwritten by subsequent calls (each function has
its own
separate storage).

Other vendor implementations of dirname() may modify the contents
of the
string passed to dirname(); this should be taken into account when
writ-
ing code which calls this function if portability is desired.

In FreeBSD 5.x the implementation has changed, but the documentation
has not. This is apparently not serious since subsequent calls to
dirname/basename check for and allocate memory using a static POINTER,
but nevertheless, the memory buffer will linger until exit time and be
reported by memory leak detector tools (such as valgrind) as a leak.

static char *bname = NULL;

if (bname == NULL) {
bname = (char *)malloc(MAXPATHLEN);
if (bname == NULL)
return(NULL);
}

I'm not sure why this change was made in 5.x but do think the
implementation change is at least worth documenting in 5.x man pages
since the functions may return NULL with ENOMEM.

To exit cleanly, applications must call dirname/basename to obtain the
static pointer and then free it.

-Ira

jpd · *nix forums Guru Joined: 22 Feb 2005 Posts: 877

Begin <1107788858.244817.188970@g14g2000cwa.googlegroups.com>
On 2005-02-07, iralee3c@gmail.com <iralee3c@gmail.com> wrote:

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