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

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Message-Id: <DA5Y65C1FEEX.1YVIUHMANNAYC@gmail.com>
Date: Mon, 26 May 2025 10:25:33 +0200
From: "Nicolas Escande" <nico.escande@...il.com>
To: "Wentao Liang" <vulab@...as.ac.cn>, <johannes@...solutions.net>,
 <luciano.coelho@...el.com>
Cc: <linux-wireless@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <stable@...r.kernel.org>
Subject: Re: [PATCH] mac80211: Add null pointer check for
 ieee80211_link_get_chanctx()

On Sun May 25, 2025 at 6:42 PM CEST, 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>
> ---
>  net/mac80211/chan.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
> index a442cb667520..9e6235001e0a 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)) {
Don't you mean 'if (WARN_ON(!old_ctx)) {'
> +				err = -EINVAL;
> +				goto out;
> +			}
>  			vif_chsw[i].vif = &link->sdata->vif;
>  			vif_chsw[i].old_ctx = &old_ctx->conf;
>  			vif_chsw[i].new_ctx = &ctx->conf;