From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 6272B156F20; Mon, 10 Nov 2025 06:28:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762756102; cv=none; b=PklsV1y74mhY5+ZI1V12zp2At0PQ5h6Wnf/ohNle78Y9P0XY2JpOw2j3S4hycptmV67yHNULX6Y2fEx+ZT6Xs7S64eJ9TZmrSjePCoVe2N97N7TuAoQgiPDVt+/YblPkqxEX/IjFwwK+LbQSMXpf99oH0hckYBUjSnIC6QCez/k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762756102; c=relaxed/simple; bh=ddIMMg0/UoErbMTX78JXcS4JAj9BwMzwkiTUhO7Nqns=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=kuWJIfytjmJMJuvRi8mcrTXYgHwX+AQz9cmb0TnJL1nL1SxT2AaCS7KG71agRPl6dKsS9i6SywmGJ2QW75e2BjpPKlA7WCt0nwp9V+75AZwlDtEE0D0FFOCTQPHNiqg2YBMg3Ni7r98kIFAAGcZ2LTxdqenxVZaCta4unifiEQo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hPDbT+y7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hPDbT+y7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 75D8DC116B1; Mon, 10 Nov 2025 06:28:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762756101; bh=ddIMMg0/UoErbMTX78JXcS4JAj9BwMzwkiTUhO7Nqns=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hPDbT+y7SDARIULk5EY9QOatLDtZNrpJ0nyknHBBTjv5z+mwJKFnycRJ1vBNgBDtl ZzYYo6RNkpWQcNIlZr6LU+maAns6QpKykxbBXRJm9rA/XX7pLDkz7p7b0cbwKlNGvz 1CH9nRFaIRQ93E0pzoMo2lFGTGZXSlHtRGSE0nY/g4InX86/4chH9kCNjiVF1k5vXC WQC/2+TyMIOmG/Qxl4C9N8rq3EU520uOgaftw0MHKQ0cB4ZwjVfmic0VkGp3IVhrXi BMTjemiDqgWffTd1p3587iB0ZXaKY0i8K+IBYhjYwUUxLd7a5Vuo6NQe+n1eDjg+/O iXWNfME8V8yOw== Date: Mon, 10 Nov 2025 06:28:17 +0000 From: Tzung-Bi Shih To: Jason Gunthorpe Cc: Benson Leung , Greg Kroah-Hartman , "Rafael J . Wysocki" , Danilo Krummrich , Jonathan Corbet , Shuah Khan , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, chrome-platform@lists.linux.dev, linux-kselftest@vger.kernel.org, Laurent Pinchart , Bartosz Golaszewski , Wolfram Sang , Simona Vetter , Dan Williams Subject: Re: [PATCH v6 1/3] revocable: Add fops replacement Message-ID: References: <20251106152712.11850-1-tzungbi@kernel.org> <20251106152712.11850-2-tzungbi@kernel.org> <20251106154715.GB1732817@nvidia.com> <20251107141509.GK1732817@nvidia.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251107141509.GK1732817@nvidia.com> On Fri, Nov 07, 2025 at 10:15:09AM -0400, Jason Gunthorpe wrote: > On Fri, Nov 07, 2025 at 05:07:54AM +0000, Tzung-Bi Shih wrote: > > On Thu, Nov 06, 2025 at 11:47:15AM -0400, Jason Gunthorpe wrote: > > > On Thu, Nov 06, 2025 at 11:27:10PM +0800, Tzung-Bi Shih wrote: > > > > +/* > > > > + * Recover the private_data to its original one. > > > > + */ > > > > +static struct fops_replacement *_recover_private_data(struct file *filp) > > > > +{ > > > > + struct fops_replacement *fr = filp->private_data; > > > > + > > > > + filp->private_data = fr->orig_private_data; > > > > + return fr; > > > > +} > > > > + > > > > +/* > > > > + * Replace the private_data to fops_replacement. > > > > + */ > > > > +static void _replace_private_data(struct fops_replacement *fr) > > > > +{ > > > > + fr->filp->private_data = fr; > > > > +} > > > > > > This switching of private_data isn't reasonable, it breaks too much > > > stuff. I think I showed a better idea in my sketch. > > > > The approach assumes the filp->private_data should be set once by the > > filp->f_op->open() if any. Is it common that the filp->private_data > > be updated in other file operations? > > You can set it once during open, but you can't change it around every > fops callback. This stuff is all concurrent. Ah, yes, I see. > > > This probably doesn't work out, is likely to make a memory leak. > > > It will be hard for the owning driver to free its per-file memory > > > without access to release. > > > > Ah, I think this reveals a drawback of the approach. > > - Without calling ->release(), some memory may leak. > > - With calling ->release(), some UAF may happen. > > It just means the user of this needs to understand there are > limitations on what release can do. Usually release just frees memory, > that is fine. > > I think it would be strange for a release to touch revocable data, > that might suggest some larger problem. I think it'd be inevitable for accessing some devm memory in ->release(), e.g. [1]. [1] https://elixir.bootlin.com/linux/v6.17/source/drivers/platform/chrome/cros_ec_chardev.c#L260