Re: [PATCH] ath9k: Prevent divide by zero kernel crash.

[Felix Fietkau <nbd@openwrt.org>]

On 2014-04-17 02:40, greearb@candelatech.com wrote:
> From: Ben Greear <greearb@candelatech.com>
> 
> Make sure we cannot ever assign beacon interval to zero.
> 
> Signed-off-by: Ben Greear <greearb@candelatech.com>
> ---
>  drivers/net/wireless/ath/ath9k/beacon.c | 4 ++++
>  drivers/net/wireless/ath/ath9k/recv.c   | 3 ++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/ath/ath9k/beacon.c b/drivers/net/wireless/ath/ath9k/beacon.c
> index 2e8bba0..5391f01 100644
> --- a/drivers/net/wireless/ath/ath9k/beacon.c
> +++ b/drivers/net/wireless/ath/ath9k/beacon.c
> @@ -443,6 +443,8 @@ static u32 ath9k_mod_tsf64_tu(u64 tsf, u32 div_tu)
>  {
>  	u32 tsf_mod, tsf_hi, tsf_lo, mod_hi, mod_lo;
>  
> +	if (WARN_ON_ONCE(div_tu == 0))
> +		div_tu = 100;
>  	tsf_mod = tsf & (BIT(10) - 1);
>  	tsf_hi = tsf >> 32;
>  	tsf_lo = ((u32) tsf) >> 10;
Why add this warning here if you already have the additions below? We
don't need multiple layers of defensive checks for the same thing.

> @@ -667,6 +669,8 @@ static void ath9k_cache_beacon_config(struct ath_softc *sc,
>  		"Caching beacon data for BSS: %pM\n", bss_conf->bssid);
>  
>  	cur_conf->beacon_interval = bss_conf->beacon_int;
> +	if (WARN_ON_ONCE(cur_conf->beacon_interval == 0))
> +		cur_conf->beacon_interval = 100;
>  	cur_conf->dtim_period = bss_conf->dtim_period;
>  	cur_conf->listen_interval = 1;
>  	cur_conf->dtim_count = 1;
> diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
> index b97217d..79c20c7 100644
> --- a/drivers/net/wireless/ath/ath9k/recv.c
> +++ b/drivers/net/wireless/ath/ath9k/recv.c
> @@ -538,7 +538,8 @@ static void ath_rx_ps_beacon(struct ath_softc *sc, struct sk_buff *skb)
>  		sc->ps_flags &= ~PS_BEACON_SYNC;
>  		ath_dbg(common, PS,
>  			"Reconfigure beacon timers based on synchronized timestamp\n");
> -		ath9k_set_beacon(sc);
> +		if (!(WARN_ON_ONCE(sc->cur_beacon_conf.beacon_interval == 0)))
> +			ath9k_set_beacon(sc);
>  	}
>  
>  	if (ath_beacon_dtim_pending_cab(skb)) {
>