From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 140043EDE46; Wed, 8 Jul 2026 09:11:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783501912; cv=none; b=daZN94+1pQThtMOmeK2bnDMJrcnj8n3N3RleIAJ9T+TScXjzZbnOY1dFlYucBCYlB6EIg2iKh6xXhmkSfxOkEVgab+IlI8WgsPuersJ02TmihkdlgwETRGe3oVKB08vBEB12Pt+9cGj2/mMnpIa2ErHTSg3L/M/87j9f07nj5+E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783501912; c=relaxed/simple; bh=l6JFG91mW4G/R7fCfssf6gK5hHZ7Nor2KNHzJAv9e7c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DOZnMQ66C11Y0ZV6GR/zDaKWP9iB+ZwLKr9g8wZVGmcPg9xL8x5e88Yf1sFHSHWRKgpm/Kw5whcwCICdPX4BHGmBa1axs7gy4R+cWtUUdror/aBHcrOgB7uZcudp3mmXjsIYqyDpoP6hZGcfUhHVC3gZpkmam+MK9dWwKxKRuaI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=BmEmoPDU; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=8LVnaRQu; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="BmEmoPDU"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="8LVnaRQu" Date: Wed, 8 Jul 2026 11:11:47 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1783501909; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=h20LA5YHcmtZeGTDYEJk05BGftpy3fA0SNQGNgHnfeQ=; b=BmEmoPDUE7RTx+O7SGa8Sfj20DHd8nsSSyeAnXbAkrIXfNnYd52ncDrPcrhUZsZLL3n4KJ NV7mHh5snAJuqdcw1CV/pMqodej5EzEsCN5rjJ+smi9c4NG+LFQN8KsGRMEqj//80ybY2h l7AT/M6Rp4TNGdMXh6aSUmCGQReGIms9I+Q8lbvK911eMGhpBjBHNSjTLvIekjc+alr+8A 1uE1nfoo3m06k9+3z8FnWkTGLeoBJT32QZBN+TsCZgMdQucW9Jz213gLfGUTdSjLyUzamE XEE7AagAEnUQyJc8y6ZT75pQLlW4xqxbV/8rtdSJIPDnLszkLhyyTlvP4LMJzw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1783501909; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=h20LA5YHcmtZeGTDYEJk05BGftpy3fA0SNQGNgHnfeQ=; b=8LVnaRQujGpEmXl1EKf5Dzy+QxRHLNbyF7X+jFHRdO/pk9s+Ca4LFbi8rLef0/CvI57MFy NQfpOW0HMJW4qZDg== From: Sebastian Andrzej Siewior To: "Paul E. McKenney" Cc: Petr Pavlu , Qingfang Deng , Breno Leitao , Norbert Szetei , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Taegu Ha , Kees Cook , linux-ppp@vger.kernel.org, linux-kernel@vger.kernel.org, Guillaume Nault , netdev@vger.kernel.org, Luis Chamberlain , Daniel Gomez , Sami Tolvanen , Aaron Tomlin , linux-modules@vger.kernel.org Subject: Re: [PATCH net v2] ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF Message-ID: <20260708091147.O1d41Vi0@linutronix.de> References: <87111f02-5b7a-4185-8364-2faba650578b@linux.dev> <20260706092926.PIlrhRKz@linutronix.de> <0dfe59c2-bf60-40fe-90e6-d6e1003709d0@suse.com> <7ff3af97-1c10-4f46-84ae-ffbf757f7e9e@paulmck-laptop> Precedence: bulk X-Mailing-List: linux-modules@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <7ff3af97-1c10-4f46-84ae-ffbf757f7e9e@paulmck-laptop> On 2026-07-07 09:39:01 [-0700], Paul E. McKenney wrote: > Alternatives include: > > o Provide a patch like that above, but only execute the > rcu_barrier() in some debug mode. If your code works when > that debug is enabled but does not otherwise, you add the > rcu_barrier(). > > o If debug is enabled, make rcu_do_batch() check the function > before invoking it. If the function is not mapped, issue a > diagnostic, and don't try to invoke the function. (But is > there a sufficiently cheap way to check for the function not > being mapped?) In both cases you would see a backtrace and the name of the last unloaded module. And since we don't see a lot of these reports, people either don't run into this because it does not exist or RCU is quick enough. > > Thanx, Paul Sebastian