netdev - Re: [PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted

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Date: Sun, 15 Oct 2023 06:53:29 +0200 (CEST)
From: Julia Lawall <julia.lawall@...ia.fr>
To: Kees Cook <keescook@...omium.org>
cc: Christophe JAILLET <christophe.jaillet@...adoo.fr>, 
    Pravin B Shelar <pshelar@....org>, "David S. Miller" <davem@...emloft.net>, 
    Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
    Paolo Abeni <pabeni@...hat.com>, 
    "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
    Nathan Chancellor <nathan@...nel.org>, 
    Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, 
    linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org, 
    netdev@...r.kernel.org, dev@...nvswitch.org, 
    linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with
 __counted_by



On Sat, 14 Oct 2023, Kees Cook wrote:

> On Sat, Oct 14, 2023 at 08:34:53AM +0200, Christophe JAILLET 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).
> >
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > ---
> > v2: Fix the subject  [Ilya Maximets]
> >     fix the field name used with __counted_by  [Ilya Maximets]
> >
> > v1: https://lore.kernel.org/all/f66ddcf1ef9328f10292ea75a17b584359b6cde3.1696156198.git.christophe.jaillet@wanadoo.fr/
> >
> >
> > This patch is part of a work done in parallel of what is currently worked
> > on by Kees Cook.
> >
> > My patches are only related to corner cases that do NOT match the
> > semantic of his Coccinelle script[1].

What was the problem with the semantic patch in this case?

thanks,
julia


> >
> > In this case, in tbl_mask_array_alloc(), several things are allocated with
> > a single allocation. Then, some pointer arithmetic computes the address of
> > the memory after the flex-array.
> >
> > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> > ---
> >  net/openvswitch/flow_table.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
> > index 9e659db78c05..f524dc3e4862 100644
> > --- a/net/openvswitch/flow_table.h
> > +++ b/net/openvswitch/flow_table.h
> > @@ -48,7 +48,7 @@ struct mask_array {
> >  	int count, max;
> >  	struct mask_array_stats __percpu *masks_usage_stats;
> >  	u64 *masks_usage_zero_cntr;
> > -	struct sw_flow_mask __rcu *masks[];
> > +	struct sw_flow_mask __rcu *masks[] __counted_by(max);
> >  };
>
> Yup, this looks correct to me. Thanks!
>
> Reviewed-by: Kees Cook <keescook@...omium.org>
>
> --
> Kees Cook
>