src/passwd/getspnam_r.c

#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <ctype.h>
#include <pthread.h>
#include "pwf.h"

/* This implementation support Openwall-style TCB passwords in place of
 * traditional shadow, if the appropriate directories and files exist.
 * Thus, it is careful to avoid following symlinks or blocking on fifos
 * which a malicious user might create in place of his or her TCB shadow
 * file. It also avoids any allocation to prevent memory-exhaustion
 * attacks via huge TCB shadow files. */

static long xatol(char **s)
{
	long x;
	if (**s == ':' || **s == '\n') return -1;
	for (x=0; **s-'0'<10U; ++*s) x=10*x+(**s-'0');
	return x;
}

int __parsespent(char *s, struct spwd *sp)
{
	sp->sp_namp = s;
	if (!(s = strchr(s, ':'))) return -1;
	*s = 0;

	sp->sp_pwdp = ++s;
	if (!(s = strchr(s, ':'))) return -1;
	*s = 0;

	s++; sp->sp_lstchg = xatol(&s);
	if (*s != ':') return -1;

	s++; sp->sp_min = xatol(&s);
	if (*s != ':') return -1;

	s++; sp->sp_max = xatol(&s);
	if (*s != ':') return -1;

	s++; sp->sp_warn = xatol(&s);
	if (*s != ':') return -1;

	s++; sp->sp_inact = xatol(&s);
	if (*s != ':') return -1;

	s++; sp->sp_expire = xatol(&s);
	if (*s != ':') return -1;

	s++; sp->sp_flag = xatol(&s);
	if (*s != '\n') return -1;
	return 0;
}

static void cleanup(void *p)
{
	fclose(p);
}

int getspnam_r(const char *name, struct spwd *sp, char *buf, size_t size, struct spwd **res)
{
	char path[20+NAME_MAX];
	FILE *f = 0;
	int rv = 0;
	int fd;
	size_t k, l = strlen(name);
	int skip = 0;
	int cs;

	*res = 0;

	/* Disallow potentially-malicious user names */
	if (*name=='.' || strchr(name, '/') || !l)
		return errno = EINVAL;

	/* Buffer size must at least be able to hold name, plus some.. */
	if (size < l+100)
		return errno = ERANGE;

	/* Protect against truncation */
	if (snprintf(path, sizeof path, "/etc/tcb/%s/shadow", name) >= sizeof path)
		return errno = EINVAL;

	fd = open(path, O_RDONLY|O_NOFOLLOW|O_NONBLOCK|O_CLOEXEC);
	if (fd >= 0) {
		struct stat st = { 0 };
		errno = EINVAL;
		if (fstat(fd, &st) || !S_ISREG(st.st_mode) || !(f = fdopen(fd, "rb"))) {
			pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
			close(fd);
			pthread_setcancelstate(cs, 0);
			return errno;
		}
	} else {
		f = fopen("/etc/shadow", "rbe");
		if (!f) return errno;
	}

	pthread_cleanup_push(cleanup, f);
	while (fgets(buf, size, f) && (k=strlen(buf))>0) {
		if (skip || strncmp(name, buf, l) || buf[l]!=':') {
			skip = buf[k-1] != '\n';
			continue;
		}
		if (buf[k-1] != '\n') {
			rv = ERANGE;
			break;
		}

		if (__parsespent(buf, sp) < 0) continue;
		*res = sp;
		break;
	}
	pthread_cleanup_pop(1);
	if (rv) errno = rv;
	return rv;
}