linux-kernel - Re: [PATCH] mwifiex: correct channel stat buffer overflows

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Date:   Fri, 30 Jun 2017 11:04:39 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Ganapathi Bhat <gbhat@...vell.com>,
        Nishant Sarmukadam <nishants@...vell.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-kernel@...r.kernel.org,
        Amitkumar Karwar <amitkarwar@...il.com>,
        linux-wireless@...r.kernel.org, stable@...r.kernel.org,
        Avinash Patil <patila@...vell.com>,
        Xinming Hu <huxm@...vell.com>
Subject: Re: [PATCH] mwifiex: correct channel stat buffer overflows

On Thu, Jun 29, 2017 at 06:23:54PM -0700, Brian Norris wrote:
> mwifiex records information about various channels as it receives scan
> information. It does this by appending to a buffer that was sized
> to the max number of supported channels on any band, but there are
> numerous problems:
> 
> (a) scans can return info from more than one band (e.g., both 2.4 and 5
>     GHz), so the determined "max" is not large enough
> (b) some firmware appears to return multiple results for a given
>     channel, so the max *really* isn't large enough
> (c) there is no bounds checking when stashing these stats, so problems
>     (a) and (b) can easily lead to buffer overflows
> 
> Let's patch this by setting a slightly-more-correct max (that accounts
> for a combination of both 2.4G and 5G bands) and adding a bounds check
> when writing to our statistics buffer.
> 
> Due to problem (b), we still might not properly report all known survey
> information (e.g., with "iw <dev> survey dump"), since duplicate results
> (or otherwise "larger than expected" results) will cause some
> truncation. But that's a problem for a future bugfix.
> 
> (And because of this known deficiency, only log the excess at the WARN
> level, since that isn't visible by default in this driver and would
> otherwise be a bit too noisy.)
> 
> Fixes: bf35443314ac ("mwifiex: channel statistics support for mwifiex")
> Cc: <stable@...r.kernel.org>
> Cc: Avinash Patil <patila@...vell.com>
> Cc: Xinming Hu <huxm@...vell.com>
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
> I've got a ton of other patches still queued up locally, and I hope to send
> them soon. But I realized this one is a nasty bug (with a trivial fix), so it's
> probably best to get this out the door quickly.

This does make sense to me.

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

> 
>  drivers/net/wireless/marvell/mwifiex/cfg80211.c | 2 +-
>  drivers/net/wireless/marvell/mwifiex/scan.c     | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/marvell/mwifiex/cfg80211.c b/drivers/net/wireless/marvell/mwifiex/cfg80211.c
> index a850ec0054e2..82f4e796ed39 100644
> --- a/drivers/net/wireless/marvell/mwifiex/cfg80211.c
> +++ b/drivers/net/wireless/marvell/mwifiex/cfg80211.c
> @@ -4219,7 +4219,7 @@ int mwifiex_init_channel_scan_gap(struct mwifiex_adapter *adapter)
>  	if (adapter->config_bands & BAND_A)
>  		n_channels_a = mwifiex_band_5ghz.n_channels;
>  
> -	adapter->num_in_chan_stats = max_t(u32, n_channels_bg, n_channels_a);
> +	adapter->num_in_chan_stats = n_channels_bg + n_channels_a;
>  	adapter->chan_stats = vmalloc(sizeof(*adapter->chan_stats) *
>  				      adapter->num_in_chan_stats);
>  
> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> index ae9630b49342..9900855746ac 100644
> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> @@ -2492,6 +2492,12 @@ mwifiex_update_chan_statistics(struct mwifiex_private *priv,
>  					      sizeof(struct mwifiex_chan_stats);
>  
>  	for (i = 0 ; i < num_chan; i++) {
> +		if (adapter->survey_idx >= adapter->num_in_chan_stats) {
> +			mwifiex_dbg(adapter, WARN,
> +				    "FW reported too many channel results (max %d)\n",
> +				    adapter->num_in_chan_stats);
> +			return;
> +		}
>  		chan_stats.chan_num = fw_chan_stats->chan_num;
>  		chan_stats.bandcfg = fw_chan_stats->bandcfg;
>  		chan_stats.flags = fw_chan_stats->flags;
> -- 
> 2.13.2.725.g09c95d1e9-goog
> 

-- 
Dmitry