linux-hardening - Re: [PATCH][next] carl9170: Fix multiple -Warray-bounds warnings

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Date:   Fri, 17 Mar 2023 20:20:41 +0100
From:   Christian Lamparter <chunkeey@...il.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kalle Valo <kvalo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] carl9170: Fix multiple -Warray-bounds warnings

On 3/17/23 18:30, Gustavo A. R. Silva wrote:
> GCC (and Clang)[1] does not like having a partially allocated object,
> since it cannot reason about it for bounds checking. Instead, fully
> allocate struct carl9170_cmd.
> 
> Fix the following warnings Seen under GCC 13:
> drivers/net/wireless/ath/carl9170/cmd.c:125:30: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[4]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:126:30: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[4]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:125:30: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[20]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:126:30: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[20]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:161:12: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[20]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:162:12: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[20]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:163:12: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[20]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:164:12: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[20]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:125:30: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[8]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:126:30: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[8]’ [-Warray-bounds=]
> drivers/net/wireless/ath/carl9170/cmd.c:220:12: warning: array subscript ‘struct carl9170_cmd[0]’ is partly outside array bounds of ‘unsigned char[8]’ [-Warray-bounds=]
> 
> Link: https://github.com/KSPP/linux/issues/268
> Link: godbolt.org/z/KP97sxh3T [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Acked-by: Christian Lamparter <chunkeey@...il.com>

> ---
>   drivers/net/wireless/ath/carl9170/cmd.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/ath/carl9170/cmd.c b/drivers/net/wireless/ath/carl9170/cmd.c
> index f2b4f537e4c1..b8ed193c0195 100644
> --- a/drivers/net/wireless/ath/carl9170/cmd.c
> +++ b/drivers/net/wireless/ath/carl9170/cmd.c
> @@ -120,7 +120,7 @@ struct carl9170_cmd *carl9170_cmd_buf(struct ar9170 *ar,
>   {
>   	struct carl9170_cmd *tmp;
>   
> -	tmp = kzalloc(sizeof(struct carl9170_cmd_head) + len, GFP_ATOMIC);
> +	tmp = kzalloc(sizeof(*tmp), GFP_ATOMIC);


This might throw-off people here. The reason this works is because carl9170_cmd struct
looks like this:
|
|struct carl9170_cmd {
|        struct carl9170_cmd_head hdr; <-- 4 bytes
|        union {
|                struct carl9170_set_key_cmd     setkey;
| [...]
|                struct carl9170_rx_filter_cmd   rx_filter;
|                u8 data[CARL9170_MAX_CMD_PAYLOAD_LEN]; <---- that's 60 bytes
|        } __packed __aligned(4);
|} __packed __aligned(4);

All commands have to fit into the command endpoint max size which is 64 bytes.