getpwent_r(3) needs gr->gr_mem to be freed, but that's not documented

[Alejandro Colomar]

On Mon, Sep 29, 2025 at 01:00:06AM +0200, Alejandro Colomar wrote:
> So far, I've written this:

[...]

I've applied some fixes to make sure that alignment is valid.  Now,
gr_mem comes first in the buffer (which also allows freeing it more
easily), and I added an explicit check about the alignment.


	// from-string get group entry
	struct group *
	sgetgrent(const char *s)
	{
		int                  e;
		size_t               n, lssize, size;
		static char          *buf = NULL;
		static struct group  grent = {};

		n = strchrcnt(s, ',') + 2;
		lssize = n * sizeof(char *);  // For 'grent.gr_mem'.
		size = lssize + strlen(s) + 1;

		free(buf);
		buf = MALLOC(size, char);
		if (buf == NULL)
			return NULL;

		e = sgetgrent_r(s, &grent, buf, size);
		if (e != 0) {
			errno = e;
			return NULL;
		}

		return &grent;
	}


	// from-string get group entry re-entrant
	int
	sgetgrent_r(size_t size;
	    const char *restrict s, struct group *restrict grent,
	    char buf[restrict size], size_t size)
	{
		char    *p, *end;
		char    *fields[4];
		size_t  n, lssize;

		if (!is_aligned(buf, char *))
			return EINVAL;
		grent->gr_mem = (char **) buf;

		// The first 'lssize' bytes of 'buf' are used for 'grent->gr_mem'.
		n = strchrcnt(s, ',') + 2;
		lssize = n * sizeof(char *);
		if (lssize >= size)
			return E2BIG;

		// The remaining bytes of 'buf' are used for a copy of 's'.
		end = buf + size;
		p = buf + lssize;
		if (stpecpy(p, end, s) == NULL)
			return errno;

		stpsep(p, "\n");

		if (STRSEP2ARR(p, ":", fields) == -1)
			return EINVAL;

		grent->gr_name = fields[0];
		grent->gr_passwd = fields[1];
		if (get_gid(fields[2], &grent->gr_gid) == -1)
			return errno;
		if (csv2ls(fields[3], n, grent->gr_mem) == -1)
			return errno;

		return 0;
	}


Cheers,
Alex

-- 
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
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