busybox/libbb/parse_mode.c

/* vi: set sw=4 ts=4: */
/*
 * parse_mode implementation for busybox
 *
 * Copyright (C) 2003  Manuel Novoa III  <mjn3@codepoet.org>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

/* http://www.opengroup.org/onlinepubs/007904975/utilities/chmod.html */

#include "libbb.h"

/* This function is used from NOFORK applets. It must not allocate anything */

#define FILEMODEBITS (S_ISUID | S_ISGID | S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)

int FAST_FUNC bb_parse_mode(const char *s, mode_t *current_mode)
{
	static const mode_t who_mask[] = {
		S_ISUID | S_ISGID | S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO, /* a */
		S_ISUID | S_IRWXU,           /* u */
		S_ISGID | S_IRWXG,           /* g */
		S_IRWXO                      /* o */
	};
	static const mode_t perm_mask[] = {
		S_IRUSR | S_IRGRP | S_IROTH, /* r */
		S_IWUSR | S_IWGRP | S_IWOTH, /* w */
		S_IXUSR | S_IXGRP | S_IXOTH, /* x */
		S_IXUSR | S_IXGRP | S_IXOTH, /* X -- special -- see below */
		S_ISUID | S_ISGID,           /* s */
		S_ISVTX                      /* t */
	};
	static const char who_chars[] ALIGN1 = "augo";
	static const char perm_chars[] ALIGN1 = "rwxXst";

	const char *p;
	mode_t wholist;
	mode_t permlist;
	mode_t new_mode;
	char op;

	if ((unsigned char)(*s - '0') < 8) {
		unsigned long tmp;
		char *e;

		tmp = strtoul(s, &e, 8);
		if (*e || (tmp > 07777U)) { /* Check range and trailing chars. */
			return 0;
		}
		*current_mode = tmp;
		return 1;
	}

	new_mode = *current_mode;

	/* Note: we allow empty clauses, and hence empty modes.
	 * We treat an empty mode as no change to perms. */

	while (*s) {	/* Process clauses. */
		if (*s == ',') {	/* We allow empty clauses. */
			++s;
			continue;
		}

		/* Get a wholist. */
		wholist = 0;
 WHO_LIST:
		p = who_chars;
		do {
			if (*p == *s) {
				wholist |= who_mask[(int)(p-who_chars)];
				if (!*++s) {
					return 0;
				}
				goto WHO_LIST;
			}
		} while (*++p);

		do {	/* Process action list. */
			if ((*s != '+') && (*s != '-')) {
				if (*s != '=') {
					return 0;
				}
				/* Since op is '=', clear all bits corresponding to the
				 * wholist, or all file bits if wholist is empty. */
				permlist = ~FILEMODEBITS;
				if (wholist) {
					permlist = ~wholist;
				}
				new_mode &= permlist;
			}
			op = *s++;

			/* Check for permcopy. */
			p = who_chars + 1;	/* Skip 'a' entry. */
			do {
				if (*p == *s) {
					int i = 0;
					permlist = who_mask[(int)(p-who_chars)]
							 & (S_IRWXU | S_IRWXG | S_IRWXO)
							 & new_mode;
					do {
						if (permlist & perm_mask[i]) {
							permlist |= perm_mask[i];
						}
					} while (++i < 3);
					++s;
					goto GOT_ACTION;
				}
			} while (*++p);

			/* It was not a permcopy, so get a permlist. */
			permlist = 0;
 PERM_LIST:
			p = perm_chars;
			do {
				if (*p == *s) {
					if ((*p != 'X')
					 || (new_mode & (S_IFDIR | S_IXUSR | S_IXGRP | S_IXOTH))
					) {
						permlist |= perm_mask[(int)(p-perm_chars)];
					}
					if (!*++s) {
						break;
					}
					goto PERM_LIST;
				}
			} while (*++p);
 GOT_ACTION:
			if (permlist) {	/* The permlist was nonempty. */
				mode_t tmp = wholist;
				if (!wholist) {
					mode_t u_mask = umask(0);
					umask(u_mask);
					tmp = ~u_mask;
				}
				permlist &= tmp;
				if (op == '-') {
					new_mode &= ~permlist;
				} else {
					new_mode |= permlist;
				}
			}
		} while (*s && (*s != ','));
	}

	*current_mode = new_mode;
	return 1;
}