During certificate verification, OpenSSL (starting from version 1.0.1n and
1.0.2b) will attempt to find an alternative certificate chain if the first
attempt to build such a chain fails. An error in the implementation of this
logic can mean that an attacker could cause certain checks on untrusted
certificates to be bypassed, such as the CA flag, enabling them to use a valid
leaf certificate to act as a CA and "issue" an invalid certificate.

This issue will impact any application that verifies certificates including
SSL/TLS/DTLS clients and SSL/TLS/DTLS servers using client authentication.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

Backport of r46285

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@46286 3c298f89-4303-0410-b956-a3cf2f4a3e73