Subject: Re: [PATCH v2] iwlegacy: 4965: fix possible out-of-bounds access in il4965_tx_cmd_build_rate()

From: Stanislaw Gruszka <[email-masked]>
Date: Sun, 27 Apr 2025 08:39:00 +0200

Hi

On Thu, Apr 24, 2025 at 09:52:44PM +0300, Alexei Safin wrote:
> Prevent out-of-bounds access in il4965_tx_cmd_build_rate() by rejecting
> rate_idx values greater than or equal to RATE_COUNT_LEGACY.
> 
> Use a correct bounds check to avoid accessing il_rates[] with
> an invalid index. The previous comparison allowed rate_idx to become
> equal to RATE_COUNT_LEGACY, which exceeds the array limit.

Thanks for the patch, however I think it's not correct.

The definitions are:

enum {
        RATE_1M_IDX = 0,
	...
	RATE_54M_INDEX,
	RATE_60M_INDEX,
	RATE_COUNT
        RATE_COUNT_LEGACY = RATE_COUNT - 1,     /* Excluding 60M */
}

extern const struct il_rate_info il_rates[RATE_COUNT];

> Replace the check 'rate_idx > RATE_COUNT_LEGACY' with
> 'rate_idx >= RATE_COUNT_LEGACY' to ensure memory safety.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.

> Fixes: 7ac9a364c172 ("iwlegacy: move under intel directory")
> Signed-off-by: Alexei Safin <[email-masked]>
> ---
> v2: change reciepent
>  drivers/net/wireless/intel/iwlegacy/4965-mac.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlegacy/4965-mac.c b/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> index 78dee8ccfebf..f60d9b9798c1 100644
> --- a/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> +++ b/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> @@ -1572,7 +1572,7 @@ il4965_tx_cmd_build_rate(struct il_priv *il,
>  	 */
>  	rate_idx = info->control.rates[0].idx;
>  	if ((info->control.rates[0].flags & IEEE80211_TX_RC_MCS) || rate_idx < 0
> -	    || rate_idx > RATE_COUNT_LEGACY)
> +	    || rate_idx >= RATE_COUNT_LEGACY)
>  		rate_idx = rate_lowest_index(&il->bands[info->band], sta);

.. so looks the check is fine already and changing it will induce a bug
for RATE_54M_INDEX.

Regards
Stanislaw

>  	/* For 5 GHZ band, remap mac80211 rate indices into driver indices */
>  	if (info->band == NL80211_BAND_5GHZ)
> -- 
> 2.39.5 (Apple Git-154)
>