Code: read_file(gchar* filepath)
{
	FILE * f;
 	size_t length;
 	gchar *ret = NULL;
 
	f = fopen(filepath, "rb");
 	if (f) {
 		fseek(f, 0, SEEK_END);
 		length = (size_t)ftell(f);
		fseek(f, 0, SEEK_SET);

		/* We can't use MALLOC since it isn't thread safe */
		ret = MALLOC(length + 1);
		if (ret) {
			if (fread(ret, length, 1, f) != 1) {
				log_message(LOG_INFO, "Failed to read all of %s", filepath);
			}
			ret[length] = '\0';
		}
		else
			log_message(LOG_INFO, "Unable to read Dbus file %s", filepath);

		fclose(f);
	}
	return ret;
}

Vulnerability Type: 
CWE ID: CWE-59
Summary: keepalived 2.0.8 didn't check for pathnames with symlinks when writing data to a temporary file upon a call to PrintData or PrintStats. This allowed local users to overwrite arbitrary files if fs.protected_symlinks is set to 0, as demonstrated by a symlink from /tmp/keepalived.data or /tmp/keepalived.stats to /etc/passwd.
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>