From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6946B367F59; Fri, 19 Jun 2026 09:56:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781862975; cv=none; b=dZDmjvwS1RBhUtu+xa4xk3JWVVjWaikfz7+jijPF8wmR5t/WrFHlzrUl87Hq9pZTQ6aR8ahDKdStlMy79kO4UpAnJNAewUiN10Hr1NVi/8xqlgJyFVK4QSc6kD7DRICJkywfZnNrq8B0kL9DKQmR2bgHHalOMI181hTqi0v5+RM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781862975; c=relaxed/simple; bh=BsgJwnB/nbLfAI8hzpc9mDJsBxbzXIhnEPJJm0gtd8E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HdSDfd9j4RSOGd7Z2a308qFwuneP8F/iKe4kwDkRJEYgvngmn0V3aVmLVY0YJtGFGrze5TVfztqVZFR5YsD5B2Ksc4FU8XWmDeHvktTRNYweFVQQWUFZnMZeHbZ1pdtnZ+ucEZqXeRJb4zF6vBhPGfnx1nUajSDq9mm0SF37lxA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=d3pWA95V; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="d3pWA95V" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A56941F000E9; Fri, 19 Jun 2026 09:56:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781862968; bh=RRAkZrz2NnBTdnmCperiOhBRhKw8kYvJMOVjYv7LxLs=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=d3pWA95VK739UMks0oDjLHDM1BwctwLXmJJfjdV1kO4NDdTFkpIVX2MBt6ZXN5D/X xTDq8qDKkcO3xghvYaWvmp1fjVahwLDxO9fEwRNuYv74rqgS1vZrtcYr0igRQUp7G6 fhN1PBXlf+32ROBPpDS6M7bvxgyfdg1ULr9ohF/M= Date: Fri, 19 Jun 2026 11:54:56 +0200 From: Greg Kroah-Hartman To: Harshit Mogalapalli Cc: stable@vger.kernel.org, patches@lists.linux.dev, Arend van Spriel , Duoming Zhou , Johannes Berg , Robert Garcia , Sasha Levin , Vegard Nossum Subject: Re: [PATCH 5.15 045/411] wifi: brcmfmac: fix use-after-free when rescheduling brcmf_btcoex_info work Message-ID: <2026061929-appendage-daughter-66d4@gregkh> References: <20260616145100.376842714@linuxfoundation.org> <20260616145102.682627807@linuxfoundation.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Jun 18, 2026 at 11:48:35PM +0530, Harshit Mogalapalli wrote: > Hi Sasha and Greg, > > On 16/06/26 20:24, Greg Kroah-Hartman wrote: > > 5.15-stable review patch. If anyone has any objections, please let me know. > > > > ------------------ > > > > From: Duoming Zhou > > > > [ Upstream commit 9cb83d4be0b9b697eae93d321e0da999f9cdfcfc ] > > > > The brcmf_btcoex_detach() only shuts down the btcoex timer, if the > > flag timer_on is false. However, the brcmf_btcoex_timerfunc(), which > > runs as timer handler, sets timer_on to false. This creates critical > > race conditions: > > > > 1.If brcmf_btcoex_detach() is called while brcmf_btcoex_timerfunc() > > is executing, it may observe timer_on as false and skip the call to > > timer_shutdown_sync(). > > > > 2.The brcmf_btcoex_timerfunc() may then reschedule the brcmf_btcoex_info > > worker after the cancel_work_sync() has been executed, resulting in > > use-after-free bugs. > > > > The use-after-free bugs occur in two distinct scenarios, depending on > > the timing of when the brcmf_btcoex_info struct is freed relative to > > the execution of its worker thread. > > > > Scenario 1: Freed before the worker is scheduled > > > > The brcmf_btcoex_info is deallocated before the worker is scheduled. > > A race condition can occur when schedule_work(&bt_local->work) is > > called after the target memory has been freed. The sequence of events > > is detailed below: > > > > CPU0 | CPU1 > > brcmf_btcoex_detach | brcmf_btcoex_timerfunc > > | bt_local->timer_on = false; > > if (cfg->btcoex->timer_on) | > > ... | > > cancel_work_sync(); | > > ... | > > kfree(cfg->btcoex); // FREE | > > | schedule_work(&bt_local->work); // USE > > > > Scenario 2: Freed after the worker is scheduled > > > > The brcmf_btcoex_info is freed after the worker has been scheduled > > but before or during its execution. In this case, statements within > > the brcmf_btcoex_handler() — such as the container_of macro and > > subsequent dereferences of the brcmf_btcoex_info object will cause > > a use-after-free access. The following timeline illustrates this > > scenario: > > > > CPU0 | CPU1 > > brcmf_btcoex_detach | brcmf_btcoex_timerfunc > > | bt_local->timer_on = false; > > if (cfg->btcoex->timer_on) | > > ... | > > cancel_work_sync(); | > > ... | schedule_work(); // Reschedule > > | > > kfree(cfg->btcoex); // FREE | brcmf_btcoex_handler() // Worker > > /* | btci = container_of(....); // USE > > The kfree() above could | ... > > also occur at any point | btci-> // USE > > during the worker's execution| > > */ | > > > > To resolve the race conditions, drop the conditional check and call > > timer_shutdown_sync() directly. It can deactivate the timer reliably, > > regardless of its current state. Once stopped, the timer_on state is > > then set to false. > > > > Fixes: 61730d4dfffc ("brcmfmac: support critical protocol API for DHCP") > > Acked-by: Arend van Spriel > > Signed-off-by: Duoming Zhou > > Link: https://patch.msgid.link/20250822050839.4413-1-duoming@zju.edu.cn > > Signed-off-by: Johannes Berg > > Signed-off-by: Robert Garcia > > Signed-off-by: Sasha Levin > > --- > > drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c | 6 ++---- > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c > > index f9f18ff451ea7c..f46e4090021777 100644 > > --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c > > +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/btcoex.c > > @@ -392,10 +392,8 @@ void brcmf_btcoex_detach(struct brcmf_cfg80211_info *cfg) > > if (!cfg->btcoex) > > return; > > - if (cfg->btcoex->timer_on) { > > - cfg->btcoex->timer_on = false; > > - del_timer_sync(&cfg->btcoex->timer); > > - } > > + del_timer_sync(&cfg->btcoex->timer); > > + cfg->btcoex->timer_on = false; > > I ran an AI assisted backport review over the 5.15.210 queue. I think this > 5.15.y backport doesn;t really try to do the same thing like upstream. Why > so ? > > Upstream 9cb83d4be0b9 uses timer_shutdown_sync() before canceling the work > and freeing cfg->btcoex: > > timer_shutdown_sync(&cfg->btcoex->timer); > cfg->btcoex->timer_on = false; > cancel_work_sync(&cfg->btcoex->work); > > The 5.15.y backport still uses del_timer_sync(): > > del_timer_sync(&cfg->btcoex->timer); > cfg->btcoex->timer_on = false; > cancel_work_sync(&cfg->btcoex->work); > > The timer code in this 5.15.y tree already documents that del_timer_sync() > cannot guarantee the timer is not rearmed by concurrent code, so the key > point is the difference between del_timer_sync() and timer_shutdown_sync(). > > I think 5.15.y should directly use timer_shutdown_sync(), as we don't have > commit: 292a089d78d3 ("treewide: Convert del_timer*() to timer_shutdown*()") > in 5.15.y, thoughts ? I think this is the best that can be done unless someone wants to backport that mess of a timer conversion. And note, I think I've rejected that backport already :) thanks, greg k-h