linux-hardening - Re: [PATCH] net: sched: Annotate struct tc_pedit with __counted

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Date: Sat, 17 Feb 2024 07:18:06 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc: Kees Cook <keescook@...omium.org>, Jakub Kicinski <kuba@...nel.org>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, "Gustavo A. R. Silva" <gustavoars@...nel.org>, netdev@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] net: sched: Annotate struct tc_pedit with __counted_by

On Fri, Feb 16, 2024 at 7:04 PM Gustavo A. R. Silva
<gustavo@...eddedor.com> wrote:
>
>
>
> On 2/16/24 17:27, Kees Cook wrote:
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> >
> > As found with Coccinelle[1], add __counted_by for struct tc_pedit.
> > Additionally, since the element count member must be set before accessing
> > the annotated flexible array member, move its initialization earlier.
> >
> > Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> > Cc: Jakub Kicinski <kuba@...nel.org>
> > Cc: Jamal Hadi Salim <jhs@...atatu.com>
> > Cc: Cong Wang <xiyou.wangcong@...il.com>
> > Cc: Jiri Pirko <jiri@...nulli.us>
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Cc: Paolo Abeni <pabeni@...hat.com>
> > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > Cc: netdev@...r.kernel.org
> > Cc: linux-hardening@...r.kernel.org
>
> `opt->nkeys` updated before `memcpy()`, looks good to me:
>
> Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Looks good to me.
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal

> Thanks!
> --
> Gustavo
>
> > ---
> >   include/uapi/linux/tc_act/tc_pedit.h | 2 +-
> >   net/sched/act_pedit.c                | 2 +-
> >   2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/linux/tc_act/tc_pedit.h b/include/uapi/linux/tc_act/tc_pedit.h
> > index f3e61b04fa01..f5cab7fc96ab 100644
> > --- a/include/uapi/linux/tc_act/tc_pedit.h
> > +++ b/include/uapi/linux/tc_act/tc_pedit.h
> > @@ -62,7 +62,7 @@ struct tc_pedit_sel {
> >       tc_gen;
> >       unsigned char           nkeys;
> >       unsigned char           flags;
> > -     struct tc_pedit_key     keys[0];
> > +     struct tc_pedit_key     keys[] __counted_by(nkeys);
> >   };
> >
> >   #define tc_pedit tc_pedit_sel
> > diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
> > index 2ef22969f274..21e863d2898c 100644
> > --- a/net/sched/act_pedit.c
> > +++ b/net/sched/act_pedit.c
> > @@ -515,11 +515,11 @@ static int tcf_pedit_dump(struct sk_buff *skb, struct tc_action *a,
> >               spin_unlock_bh(&p->tcf_lock);
> >               return -ENOBUFS;
> >       }
> > +     opt->nkeys = parms->tcfp_nkeys;
> >
> >       memcpy(opt->keys, parms->tcfp_keys,
> >              flex_array_size(opt, keys, parms->tcfp_nkeys));
> >       opt->index = p->tcf_index;
> > -     opt->nkeys = parms->tcfp_nkeys;
> >       opt->flags = parms->tcfp_flags;
> >       opt->action = p->tcf_action;
> >       opt->refcnt = refcount_read(&p->tcf_refcnt) - ref;