xfrm: refine validation of template and selector families

xfrm: refine validation of template and selector families

BugLink: https://bugs.launchpad.net/bugs/1837664
commit 35e6103861a3a970de6c84688c6e7a1f65b164ca upstream.

The check assumes that in transport mode, the first templates family
must match the address family of the policy selector.

Syzkaller managed to build a template using MODE_ROUTEOPTIMIZATION,
with ipv4-in-ipv6 chain, leading to following splat:

BUG: KASAN: stack-out-of-bounds in xfrm_state_find+0x1db/0x1854
Read of size 4 at addr ffff888063e57aa0 by task a.out/2050
 xfrm_state_find+0x1db/0x1854
 xfrm_tmpl_resolve+0x100/0x1d0
 xfrm_resolve_and_create_bundle+0x108/0x1000 [..]

Problem is that addresses point into flowi4 struct, but xfrm_state_find
treats them as being ipv6 because it uses templ->encap_family is used
(AF_INET6 in case of reproducer) rather than family (AF_INET).

This patch inverts the logic: Enforce 'template family must match
selector' EXCEPT for tunnel and BEET mode.

In BEET and Tunnel mode, xfrm_tmpl_resolve_one will have remote/local
address pointers changed to point at the addresses found in the template,
rather than the flowi ones, so no oob read will occur.

Reported-by: 3ntr0py1337@gmail.com
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>