netdev - Re: [PATCH] wifi: mac80211: Don't finalize CSA in IBSS mode if state is disconnected

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Date:   Thu, 25 Aug 2022 01:41:36 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     Siddh Raman Pant <code@...dh.me>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-kernel-mentees 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        syzbot+b6c9fe29aefe68e4ad34@...kaller.appspotmail.com
Subject: Re: [PATCH] wifi: mac80211: Don't finalize CSA in IBSS mode if state is disconnected

On Sun, 14 Aug 2022 20:45:12 +0530  Siddh Raman Pant  wrote:
> When we are not connected to a channel, sending channel "switch"
> announcement doesn't make any sense.
> 
> The BSS list is empty in that case. This causes the for loop in
> cfg80211_get_bss() to be bypassed, so the function returns NULL
> (check line 1424 of net/wireless/scan.c), causing the WARN_ON()
> in ieee80211_ibss_csa_beacon() to get triggered (check line 500
> of net/mac80211/ibss.c), which was consequently reported on the
> syzkaller dashboard.
> 
> Thus, check if we have an existing connection before generating
> the CSA beacon in ieee80211_ibss_finish_csa().
> 
> Fixes: cd7760e62c2a ("mac80211: add support for CSA in IBSS mode")
> Bug report: https://syzkaller.appspot.com/bug?id=05603ef4ae8926761b678d2939a3b2ad28ab9ca6
> Reported-by: syzbot+b6c9fe29aefe68e4ad34@...kaller.appspotmail.com
> Cc: stable@...r.kernel.org

Tested-by: syzbot+b6c9fe29aefe68e4ad34@...kaller.appspotmail.com

Syzbot is now booting properly and the test ran successfully.

Thanks,
Siddh

> Signed-off-by: Siddh Raman Pant <code@...dh.me>
> ---
> The fixes commit is old, and syzkaller shows the problem exists for
> 4.19 and 4.14 as well, so CC'd stable list.
> 
>  net/mac80211/ibss.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/mac80211/ibss.c b/net/mac80211/ibss.c
> index d56890e3fabb..9b283bbc7bb4 100644
> --- a/net/mac80211/ibss.c
> +++ b/net/mac80211/ibss.c
> @@ -530,6 +530,10 @@ int ieee80211_ibss_finish_csa(struct ieee80211_sub_if_data *sdata)
>  
>  	sdata_assert_lock(sdata);
>  
> +	/* When not connected/joined, sending CSA doesn't make sense. */
> +	if (ifibss->state != IEEE80211_IBSS_MLME_JOINED)
> +		return -ENOLINK;
> +
>  	/* update cfg80211 bss information with the new channel */
>  	if (!is_zero_ether_addr(ifibss->bssid)) {
>  		cbss = cfg80211_get_bss(sdata->local->hw.wiphy,
> -- 
> 2.35.1