Code: check_acl(pam_handle_t *pamh,
	  const char *sense, const char *this_user, const char *other_user,
	  int noent_code, int debug)
{
        struct passwd *pwd;
        FILE *fp = NULL;
        int i, fd = -1, save_errno;
       uid_t fsuid;
        struct stat st;
        /* Check this user's <sense> file. */
        pwd = pam_modutil_getpwnam(pamh, this_user);
        if (pwd == NULL) {
		pam_syslog(pamh, LOG_ERR,
			   "error determining home directory for '%s'",
			   this_user);
		return PAM_SESSION_ERR;
	}
	/* Figure out what that file is really named. */
	i = snprintf(path, sizeof(path), "%s/.xauth/%s", pwd->pw_dir, sense);
	if ((i >= (int)sizeof(path)) || (i < 0)) {
		pam_syslog(pamh, LOG_ERR,
                           "name of user's home directory is too long");
                return PAM_SESSION_ERR;
        }
       fsuid = setfsuid(pwd->pw_uid);
        if (!stat(path, &st)) {
                if (!S_ISREG(st.st_mode))
                        errno = EINVAL;
			fd = open(path, O_RDONLY | O_NOCTTY);
                        fd = open(path, O_RDONLY | O_NOCTTY);
        }
        save_errno = errno;
       setfsuid(fsuid);
        if (fd >= 0) {
                if (!fstat(fd, &st)) {
                        if (!S_ISREG(st.st_mode))
			save_errno = errno;
			close(fd);
		}
	}
	if (fp) {
		char buf[LINE_MAX], *tmp;
		/* Scan the file for a list of specs of users to "trust". */
		while (fgets(buf, sizeof(buf), fp) != NULL) {
			tmp = memchr(buf, '\r', sizeof(buf));
			if (tmp != NULL) {
				*tmp = '\0';
			}
			tmp = memchr(buf, '\n', sizeof(buf));
			if (tmp != NULL) {
				*tmp = '\0';
			}
			if (fnmatch(buf, other_user, 0) == 0) {
				if (debug) {
					pam_syslog(pamh, LOG_DEBUG,
						   "%s %s allowed by %s",
						   other_user, sense, path);
				}
				fclose(fp);
				return PAM_SUCCESS;
			}
		}
		/* If there's no match in the file, we fail. */
		if (debug) {
			pam_syslog(pamh, LOG_DEBUG, "%s not listed in %s",
				   other_user, path);
		}
		fclose(fp);
		return PAM_PERM_DENIED;
	} else {
		/* Default to okay if the file doesn't exist. */
	        errno = save_errno;
		switch (errno) {
		case ENOENT:
			if (noent_code == PAM_SUCCESS) {
				if (debug) {
					pam_syslog(pamh, LOG_DEBUG,
						   "%s does not exist, ignoring",
						   path);
				}
			} else {
				if (debug) {
					pam_syslog(pamh, LOG_DEBUG,
						   "%s does not exist, failing",
						   path);
				}
			}
			return noent_code;
		default:
			if (debug) {
				pam_syslog(pamh, LOG_DEBUG,
					   "error opening %s: %m", path);
			}
			return PAM_PERM_DENIED;
		}
	}
}

Vulnerability Type: +Info
CWE ID: 
Summary: The privilege-dropping implementation in the (1) pam_env and (2) pam_mail modules in Linux-PAM (aka pam) 1.1.2 does not check the return value of the setfsuid system call, which might allow local users to obtain sensitive information by leveraging an unintended uid, as demonstrated by a symlink attack on the .pam_environment file in a user's home directory.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2010-3435.
Commit Message: 