linux-kernel - Re: [PATCH v2] mac80211: Add null pointer check for ieee80211_link_get

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Message-ID: <2025052614-spring-ether-8d09@gregkh>
Date: Mon, 26 May 2025 11:44:42 +0200
From: Greg KH <greg@...ah.com>
To: Wentao Liang <vulab@...as.ac.cn>
Cc: johannes@...solutions.net, luciano.coelho@...el.com,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2] mac80211: Add null pointer check for
 ieee80211_link_get_chanctx()

On Mon, May 26, 2025 at 05:19:03PM +0800, Wentao Liang wrote:
> The function ieee80211_chsw_switch_vifs() calls the function
> ieee80211_link_get_chanctx(), but does not check its return value.
> The return value is a null pointer if the ieee80211_link_get_chanctx()
> fails. This will lead to a null pointer dereference in the following
> code "&old_ctx->conf". A proper implementation can be found in
> ieee80211_link_use_reserved_assign().
> 
> Add a null pointer check and goto error handling path if the
> function fails.
> 
> Fixes: 5d52ee811019 ("mac80211: allow reservation of a running chanctx")
> Cc: stable@...r.kernel.org # v3.16
> Signed-off-by: Wentao Liang <vulab@...as.ac.cn>
> ---
> v2: Fix code error.
> 
>  net/mac80211/chan.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
> index a442cb667520..c9b703c283e7 100644
> --- a/net/mac80211/chan.c
> +++ b/net/mac80211/chan.c
> @@ -1503,6 +1503,10 @@ static int ieee80211_chsw_switch_vifs(struct ieee80211_local *local,
>  				continue;
>  
>  			old_ctx = ieee80211_link_get_chanctx(link);
> +			if (WARN_ON(!old_ctx)) {

You just caused the machine to crash and reboot on billions of Linux
systems if this ever is triggered.  So please never do that :(

thanks,

greg k-h