linux-hardening - Re: [PATCH][next] rxrpc: Replace fake flex-array with flexible-array member

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Date:   Fri, 21 Apr 2023 09:00:48 -0400
From:   Jeffrey E Altman <jaltman@...istor.com>
To:     "Gustavo A. R. Silva (gustavoars@...nel.org)" <gustavoars@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Marc Dionne <marc.dionne@...istor.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     linux-afs@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] rxrpc: Replace fake flex-array with flexible-array
 member

On 3/6/2023 3:57 PM, Gustavo A. R. Silva (gustavoars@...nel.org) wrote:
> Zero-length arrays as fake flexible arrays are deprecated and we are
> moving towards adopting C99 flexible-array members instead.
>
> Transform zero-length array into flexible-array member in struct
> rxrpc_ackpacket.
>
> Address the following warnings found with GCC-13 and
> -fstrict-flex-arrays=3 enabled:
> net/rxrpc/call_event.c:149:38: warning: array subscript i is outside array bounds of ‘uint8_t[0]’ {aka ‘unsigned char[]’} [-Warray-bounds=]
>
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [1].
>
> Link: https://github.com/KSPP/linux/issues/21
> Link: https://github.com/KSPP/linux/issues/263
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>   net/rxrpc/protocol.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/rxrpc/protocol.h b/net/rxrpc/protocol.h
> index 6760cb99c6d6..e8ee4af43ca8 100644
> --- a/net/rxrpc/protocol.h
> +++ b/net/rxrpc/protocol.h
> @@ -126,7 +126,7 @@ struct rxrpc_ackpacket {
>   	uint8_t		nAcks;		/* number of ACKs */
>   #define RXRPC_MAXACKS	255
>   
> -	uint8_t		acks[0];	/* list of ACK/NAKs */
> +	uint8_t		acks[];		/* list of ACK/NAKs */
>   #define RXRPC_ACK_TYPE_NACK		0
>   #define RXRPC_ACK_TYPE_ACK		1
>   

Reviewed-by: Jeffrey Altman <jaltman@...istor.com>



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