Subject: Re: [PATCH] wifi: iwlegacy: Check rate_idx range after addition

From: Stanislaw Gruszka <[email-masked]>
Date: Sat, 17 May 2025 16:53:53 +0200

Hi Fedor, thanks for review,

On Sat, May 17, 2025 at 03:21:03PM +0300, Fedor Pchelkin wrote:
> On Sat, 17. May 09:40, Stanislaw Gruszka wrote:
> > Move rate_idx range check after we add IL_FIRST_OFDM_RATE for it
> > for 5GHz band.
> > 
> > Additionally use ">= RATE_COUNT" check instead of "> RATE_COUNT_LEGACY"
> > to avoid possible reviewers and static code analyzers confusion about
> > size of il_rate array.
> > 
> > Reported-by: Fedor Pchelkin <[email-masked]>
> > Reported-by: Alexei Safin <[email-masked]>
> > Signed-off-by: Stanislaw Gruszka <[email-masked]>
> > ---
> 
> Thank you for the patch, Stanislaw!
> 
> Please see some comments below.
> 
> >  drivers/net/wireless/intel/iwlegacy/4965-mac.c | 15 +++++++++------
> >  1 file changed, 9 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/net/wireless/intel/iwlegacy/4965-mac.c b/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> > index dc8c408902e6..2294ea43b4c7 100644
> > --- a/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> > +++ b/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> > @@ -1567,16 +1567,19 @@ il4965_tx_cmd_build_rate(struct il_priv *il,
> >  	/**
> >  	 * If the current TX rate stored in mac80211 has the MCS bit set, it's
> >  	 * not really a TX rate.  Thus, we use the lowest supported rate for
> > -	 * this band.  Also use the lowest supported rate if the stored rate
> > -	 * idx is invalid.
> > +	 * this band.
> >  	 */
> >  	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)
> > +	if (info->control.rates[0].flags & IEEE80211_TX_RC_MCS)
> >  		rate_idx = rate_lowest_index(&il->bands[info->band], sta);
> > -	/* For 5 GHZ band, remap mac80211 rate indices into driver indices */
> > -	if (info->band == NL80211_BAND_5GHZ)
> > +	else if (info->band == NL80211_BAND_5GHZ)
> 
> 5GHZ shouldn't be in 'else if' clause, I think. Is it mutually exclusive
> with IEEE80211_TX_RC_MCS ?

Right, this is wrong. I thought we can use index returned by
rate_lowest_index() but we still should add IL_FIRST_OFDM_RATE.
At least this is how is done now.

> 
> > +		/* For 5 GHZ band, remap mac80211 rate indices into driver indices */
> >  		rate_idx += IL_FIRST_OFDM_RATE;
> > +
> > +	/* Use the lowest supported rate if the stored rate idx is invalid. */
> > +	if (rate_idx < 0 || rate_idx >= RATE_COUNT)
> 
> There is a check inside il4965_rs_get_rate():
> 
> 	/* Check for invalid rates */
> 	if (rate_idx < 0 || rate_idx >= RATE_COUNT_LEGACY ||
> 	    (sband->band == NL80211_BAND_5GHZ &&
> 	     rate_idx < IL_FIRST_OFDM_RATE))
> 		rate_idx = rate_lowest_index(sband, sta);
> 
> so RATE_COUNT_LEGACY (60M) is considered invalid there but is accepted
> here in il4965_tx_cmd_build_rate(). It looks strange, at least for the
> fresh reader as me..

Indeed this is strange. I'm not sure why those checks differ.

Anyway for the rate_idx in il4965_tx_cmd_build_rate()
for 5GHs I'll just add additional check like below:

	if (info->band == NL80211_BAND_5GHZ) {
		rate_idx += IL_FIRST_OFDM_RATE;
		if (rate_idx > IL_LAST_OFDM_RATE);
			rate_idx = IL_LAST_OFDM_RATE;
	}

This patch should be dropped.

Regards
Stanislaw