From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4DF06C87FD2 for ; Thu, 31 Jul 2025 10:29:07 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D370610E75C; Thu, 31 Jul 2025 10:29:05 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="P/GYwEKm"; dkim-atps=neutral Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9166710E75C; Thu, 31 Jul 2025 10:29:04 +0000 (UTC) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 5045A5C60AB; Thu, 31 Jul 2025 10:29:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F236C4CEEF; Thu, 31 Jul 2025 10:29:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753957743; bh=dQpgp/BHvTQBqY1GaITEs3hvMmnvJ62dCMrJ3vnLpnk=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=P/GYwEKm+QWPfbB4s73gDJR4YuMaffBmI2uBiWepB1D9Dk5oBZtfrvSx/wkieKpJu P9bJbzkAsSIansjIGjRVmzXpr3p0eSt4EUdYaqDT/9/KKb1M4bVOSr6AhASgxVxCiW lEkgKU+oC3z5A+GSMjD4RpEUZetw+Ki7kdgw4ObIjNHyDKYQ2vExYpnhoCM+6us2+e e3JTfI4Et2P9AFlEpXQa0ZkoK2ivzzEmoD5EjDv12jejDd0dyqCaHUHFlI+V7BgBxQ BoPanSxjL98wxR3MtCrVl/+gPGG+i8FkZcj0IJcG4PBbsmpSbpVEVrm9pmAPiAEE0N R3CFjbLkNWQHg== Message-ID: <6270c853cdf90172d4794e2b601ebc88590b774f.camel@kernel.org> Subject: Re: [PATCH v15 6/9] ref_tracker: automatically register a file in debugfs for a ref_tracker_dir From: Jeff Layton To: Kees Cook Cc: Andrew Morton , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Krzysztof Karas , Kuniyuki Iwashima , Qasim Ijaz , Nathan Chancellor , Andrew Lunn , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org Date: Thu, 31 Jul 2025 06:29:00 -0400 In-Reply-To: <202507301603.62E553F93@keescook> References: <20250618-reftrack-dbgfs-v15-0-24fc37ead144@kernel.org> <20250618-reftrack-dbgfs-v15-6-24fc37ead144@kernel.org> <202507301603.62E553F93@keescook> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Wed, 2025-07-30 at 16:07 -0700, Kees Cook wrote: > On Wed, Jun 18, 2025 at 10:24:19AM -0400, Jeff Layton wrote: > > [...] > > The file is given the name "class@%px", as having the unmodified addres= s > > is helpful for debugging. This should be safe since this directory is o= nly > > accessible by root > > [...] > > +void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir) > > +{ > > + char name[NAME_MAX + 1]; > > + struct dentry *dentry; > > + int ret; > > + > > + /* No-op if already created */ > > + dentry =3D xa_load(&debugfs_dentries, (unsigned long)dir); > > + if (dentry && !xa_is_err(dentry)) > > + return; > > + > > + ret =3D snprintf(name, sizeof(name), "%s@%px", dir->class, dir); > > + name[sizeof(name) - 1] =3D '\0'; >=20 > Yikes! Never use %px, and especially don't use it for a stable > identifier nor expose it to userspace like this. If you absolutely must, > use %p, but never %px. This is a kernel address leak: > https://docs.kernel.org/process/deprecated.html#p-format-specifier >=20 > "helpful for debugging" is not a sufficiently good reason; and "only > accessible by root" has nothing to do with kernel address integrity. > Those kinds of things are (roughly) managed by various capabilities, > not DAC uid=3D=3D0. >From the link above: "If you think you can justify it (in comments and commit log) well enough to stand up to Linus=E2=80=99s scrutiny, maybe you can use =E2=80=9C= %px=E2=80=9D, along with making sure you have sensible permissions." Is making it only accessible by root not sensible enough? What are "sensible permissions" in this instance? Those questions asked, I'm not dead-set on using %px here. I just figured it would be more convenient to have the actual address if you needed to go poke around with drgn. We can change it to %p (or something else) if it's really a problem. --=20 Jeff Layton