[Regression?] iptables broken on 32bit with pre-4.7-rc

From: John Stultz
Date: Thu May 26 2016 - 01:52:43 EST

Hey Florian, Pablo,

In updating a 32bit arm device from 4.6 to Linus' current HEAD, I
noticed I was having some trouble with networking, and realized that
/proc/net/ip_tables_names was suddenly empty.

Digging through the registration process, it seems we're catching on the:

if (strcmp(t->u.user.name, XT_STANDARD_TARGET) == 0 &&
target_offset + sizeof(struct xt_standard_target) != next_offset)
return -EINVAL;

check added in 7ed2abddd20cf ("netfilter: x_tables: check standard
target size too").

Where next_offset seems to be 4 bytes larger then the the offset +
standard_target struct size.

Commenting out those checks (the commit doesn't revert cleanly), seems
to get things going again for me.

I'm not exactly sure how the next_offset value is set, so I'm hoping
the proper fix is more obvious to one of you.