[SRU X/B/D/E/F] CVE-2020-10711

[Thadeu Lima de Souza Cascardo]

Description:
 A NULL pointer dereference issue was found in the Linux kernel's SELinux
 subsystem. It occurs while importing the Commercial IP Security Option
 (CIPSO) protocol's category bitmap into SELinux's extensible bitmap via
 'ebitmap_netlbl_import' routine.  While parsing the CIPSO restricted bitmap
 tag in 'cipso_v4_parsetag_rbm' routine, it sets the security attribute flag
 to indicate that category bitmap is present, even if it has not been
 allocated. This leads to the said NULL pointer dereference issue while
 importing the same category bitmap into SELinux. A remote network user
 could use this flaw to crash the system kernel resulting in DoS scenario.

This was built tested for all series, a clean cherry-pick save for Xenial,
where IPv6 CALIPSO is not supported.