Re: [ath5k-devel] [PATCH 1/1] ath5k: fix hw rate index condition

Luis R. Rodriguez
2009-02-27T02:40:16Z

On Thu, Feb 26, 2009 at 06:27:04PM -0800, Bob Copeland wrote:
> On Fri, Feb 27, 2009 at 12:32:55AM +0100, Jiri Slaby wrote:
> > On 27.2.2009 00:28, Bob Copeland wrote:
> >> hw_to_driver_rix() returns sc->rate_idx[x][y] as an int, and that
> >> array is initialized to (u8)-1 for invalid rates. So, it can
> >> return 255 if the hardware rate index (y) is bad, then the check
> >> "rxs.rate_idx>= 0" would always be true, right? If it's not a
> >> real bug yet, it likely will be one day :)
> >
> > Ah, yes, it really is a bug(tm), care to post a fix?
>
> Actually, I remembered in the dark recesses of my moldering brain
> that someone had a lost patch for this a while ago, so I searched
> the archives. Pavel, ok to add your s-o-b?
>
> From: Pavel Roskin <proski@gnu.org>
> Subject: [PATCH] ath5k: use signed elements for rate index table
>
> A lookup table is used to convert from hardware rate indexes back
> to driver-based rate indexes. For unknown hardware rates, we
> initialize these values to -1, but since the array elements are of
> type u8, they will be in the range 0-255. This can cause array
> overruns because subsequent sanity checks only check for negative
> values.
>
> Signed-off-by: Bob Copeland <me@bobcopeland.com>
> ---
> drivers/net/wireless/ath5k/base.h | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/net/wireless/ath5k/base.h b/drivers/net/wireless/ath5k/base.h
> index 20e0d14..8229561 100644
> --- a/drivers/net/wireless/ath5k/base.h
> +++ b/drivers/net/wireless/ath5k/base.h
> @@ -112,7 +112,7 @@ struct ath5k_softc {
> struct ieee80211_supported_band sbands[IEEE80211_NUM_BANDS];
> struct ieee80211_channel channels[ATH_CHAN_MAX];
> struct ieee80211_rate rates[IEEE80211_NUM_BANDS][AR5K_MAX_RATES];
> - u8 rate_idx[IEEE80211_NUM_BANDS][AR5K_MAX_RATES];
> + s8 rate_idx[IEEE80211_NUM_BANDS][AR5K_MAX_RATES];

Might be worth adding a note why this is the case. Can't we simply avoid
this by checking earlier for the error or simply assigning it an actual
default _good_ hw rate value?

Luis