Re: [PATCH] skbuff: Switch structure bounds to struct_group()

On Thu, Nov 18, 2021 at 11:13:55PM -0800, Jakub Kicinski wrote:

On Thu, 18 Nov 2021 10:36:15 -0800 Kees Cook wrote:

quoted

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Replace the existing empty member position markers "headers_start" and
"headers_end" with a struct_group(). This will allow memcpy() and sizeof()
to more easily reason about sizes, and improve readability.

"pahole" shows no size nor member offset changes to struct sk_buff.
"objdump -d" shows no object code changes (outside of WARNs affected by
source line number changes).

This adds ~27k of these warnings to W=1 gcc builds:

include/linux/skbuff.h:851:1: warning: directive in macro's argument list

Hrm, I can't reproduce this, using several GCC versions and net-next. What
compiler version[1] and base commit[2] were used here?

-Kees

[1] https://github.com/kuba-moo/nipa/pull/10
[2] https://github.com/kuba-moo/nipa/pull/11

-- 
Kees Cook