UPSTREAM: netfilter: add back stackpointer size checks

commit 57ebd808a97d7c5b1e1afb937c2db22beba3c1f8 upstream.

The rationale for removing the check is only correct for rulesets
generated by ip(6)tables.

In iptables, a jump can only occur to a user-defined chain, i.e.
because we size the stack based on number of user-defined chains we
cannot exceed stack size.

However, the underlying binary format has no such restriction,
and the validation step only ensures that the jump target is a
valid rule start point.

IOW, its possible to build a rule blob that has no user-defined
chains but does contain a jump.

If this happens, no jump stack gets allocated and crash occurs
because no jumpstack was allocated.

BUG=b:76437909
TEST=trybot

Fixes: 7814b6ec6d0d6 ("netfilter: xtables: don't save/restore jumpstack offset")
Reported-by: syzbot+e783f671527912cd9403@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit 48db3004d40d97d3ac205d2d64ab580a8cfcfe63)
Signed-off-by: Daniel Wang <wonderfly@google.com>

Change-Id: Ib9774a938f291454bd3dc06b3177fbcb6d31a8f0
Reviewed-on: https://chromium-review.googlesource.com/981017
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Tested-by: Daniel Wang <wonderfly@google.com>
Commit-Queue: Daniel Wang <wonderfly@google.com>
3 files changed