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Initial revision

/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <paths.h>
#include <unistd.h>

extern char **environ;

int
execvp(const char *name, char * const *argv)
{
	const char **memp;
	int cnt;
	size_t lp, ln = 0;
	int eacces = 0;
	unsigned int etxtbsy = 0;
	char buf[PATH_MAX];
	const char *bp, *path, *p;

	/* "" is not a valid filename; check this before traversing PATH. */
	if (name[0] == '\0') {
		errno = ENOENT;
		goto done;
	}
	/* If it's an absolute or relative path name, it's easy. */
	if (strchr(name, '/')) {
		bp = name;
		path = "";
		goto retry;
	}
	bp = buf;

	/* Get the path we're searching. */
	if (!(path = getenv("PATH")))
		path = _PATH_DEFPATH;

	ln = strlen(name);
	do {
		/* Find the end of this path element. */
		for (p = path; *path != 0 && *path != ':'; path++)
			continue;
		/*
		 * It's a SHELL path -- double, leading and trailing colons
		 * mean the current directory.
		 */
		if (p == path) {
			p = ".";
			lp = 1;
		} else
			lp = path - p;

		/*
		 * If the path is too long complain.  This is a possible
		 * security issue; given a way to make the path too long
		 * the user may execute the wrong program.
		 */
		if (lp + ln + 2 > sizeof(buf))
			continue;
		memcpy(buf, p, lp);
		buf[lp] = '/';
		memcpy(buf + lp + 1, name, ln);
		buf[lp + ln + 1] = '\0';

retry:		(void)execve(bp, argv, environ);
		switch (errno) {
		case EACCES:
			eacces = 1;
			break;
		case ENOTDIR:
		case ENOENT:
			break;
		case ENOEXEC:
			for (cnt = 0; argv[cnt] != NULL; ++cnt)
				continue;
			if ((memp = alloca((cnt + 2) * sizeof(*memp))) == NULL)
				goto done;
			memp[0] = _PATH_BSHELL;
			memp[1] = bp;
			(void)memcpy(&memp[2], &argv[1], cnt * sizeof(*memp));
			(void)execve(_PATH_BSHELL, (char * const *)memp,
			    environ);
			goto done;
		case ETXTBSY:
			if (etxtbsy < 3)
				(void)sleep(++etxtbsy);
			goto retry;
		default:
			goto done;
		}
	} while (*path++ == ':');	/* Otherwise, *path was NUL */
	if (eacces)
		errno = EACCES;
	else if (!errno)
		errno = ENOENT;
done:
	return (-1);
}