linux-hardening - Re: [ovs-dev] [PATCH net-next 2/2] net: openvswitch: Annotate struct mask_array with __counted_byUse struct

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Message-ID: <689fe81f-e2b4-9f99-4005-8ae330afb869@ovn.org>
Date: Mon, 2 Oct 2023 18:51:53 +0200
From: Ilya Maximets <i.maximets@....org>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>,
 keescook@...omium.org, 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>
Cc: dev@...nvswitch.org, netdev@...r.kernel.org, llvm@...ts.linux.dev,
 kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org, i.maximets@....org
Subject: Re: [ovs-dev] [PATCH net-next 2/2] net: openvswitch: Annotate struct
 mask_array with __counted_byUse struct_size()

On 10/1/23 13:07, 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>
> ---
> 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].
> 
> 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..8d9e83b4d62c 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(size);

Did you mean 'max'?  There is no 'size' in the structure.

Also, the patch subject is messed up a bit.

Best regards, Ilya Maximets.