Code:  vrrp_print_data(void)
 {
	FILE *file = fopen (dump_file, "w");
 
 	if (!file) {
 		log_message(LOG_INFO, "Can't open %s (%d: %s)",
			dump_file, errno, strerror(errno));
		return;
	}

	dump_data_vrrp(file);

	fclose(file);
}

Commit Message: When opening files for write, ensure they aren't symbolic links

Issue #1048 identified that if, for example, a non privileged user
created a symbolic link from /etc/keepalvied.data to /etc/passwd,
writing to /etc/keepalived.data (which could be invoked via DBus)
would cause /etc/passwd to be overwritten.

This commit stops keepalived writing to pathnames where the ultimate
component is a symbolic link, by setting O_NOFOLLOW whenever opening
a file for writing.

This might break some setups, where, for example, /etc/keepalived.data
was a symbolic link to /home/fred/keepalived.data. If this was the case,
instead create a symbolic link from /home/fred/keepalived.data to
/tmp/keepalived.data, so that the file is still accessible via
/home/fred/keepalived.data.

There doesn't appear to be a way around this backward incompatibility,
since even checking if the pathname is a symbolic link prior to opening
for writing would create a race condition.

Signed-off-by: Quentin Armitage <quentin@armitage.org.uk>
CWE ID: CWE-59
 vrrp_print_data(void)
 {
	FILE *file = fopen_safe(dump_file, "w");
 
 	if (!file) {
 		log_message(LOG_INFO, "Can't open %s (%d: %s)",
			dump_file, errno, strerror(errno));
		return;
	}

	dump_data_vrrp(file);

	fclose(file);
}
