linux-hardening - Re: [PATCH 1/5] chelsio/l2t: Annotate struct l2t_data with __counted

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Date: Sat, 30 Sep 2023 08:39:42 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Kees Cook <keescook@...omium.org>, Raju Rangoju <rajur@...lsio.com>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 "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, linux-hardening@...r.kernel.org,
 llvm@...ts.linux.dev
Subject: Re: [PATCH 1/5] chelsio/l2t: Annotate struct l2t_data with
 __counted_by

Le 29/09/2023 à 20:11, Kees Cook a écrit :
> 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 l2t_data.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Raju Rangoju <rajur@...lsio.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>   drivers/net/ethernet/chelsio/cxgb3/l2t.h | 2 +-
>   drivers/net/ethernet/chelsio/cxgb4/l2t.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/chelsio/cxgb3/l2t.h b/drivers/net/ethernet/chelsio/cxgb3/l2t.h
> index ea75f275023f..646ca0bc25bd 100644
> --- a/drivers/net/ethernet/chelsio/cxgb3/l2t.h
> +++ b/drivers/net/ethernet/chelsio/cxgb3/l2t.h
> @@ -76,7 +76,7 @@ struct l2t_data {
>   	atomic_t nfree;		/* number of free entries */
>   	rwlock_t lock;
>   	struct rcu_head rcu_head;	/* to handle rcu cleanup */
> -	struct l2t_entry l2tab[];
> +	struct l2t_entry l2tab[] __counted_by(nentries);
>   };
>   
>   typedef void (*arp_failure_handler_func)(struct t3cdev * dev,
> diff --git a/drivers/net/ethernet/chelsio/cxgb4/l2t.c b/drivers/net/ethernet/chelsio/cxgb4/l2t.c
> index a10a6862a9a4..1e5f5b1a22a6 100644
> --- a/drivers/net/ethernet/chelsio/cxgb4/l2t.c
> +++ b/drivers/net/ethernet/chelsio/cxgb4/l2t.c
> @@ -59,7 +59,7 @@ struct l2t_data {
>   	rwlock_t lock;
>   	atomic_t nfree;             /* number of free entries */
>   	struct l2t_entry *rover;    /* starting point for next allocation */
> -	struct l2t_entry l2tab[];  /* MUST BE LAST */
> +	struct l2t_entry l2tab[] __counted_by(l2t_size);  /* MUST BE LAST */

Nit: the comment is maybe unneeded.

>   };
>   
>   static inline unsigned int vlan_prio(const struct l2t_entry *e)