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 4FC253B8D5C; Thu, 5 Feb 2026 12:38:55 +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=1770295135; cv=none; b=OoqVnDVoEBfbqE9Hjr8l3ATTjpNKf3a8Osgz77TckD0bMOyz4Bs2Uqus+VhHh3Y6aLJyrMICwH4myPPOz458aj9CpUhS/XvW7YF4WN9Vo6yWkiuJxvuQl+4uQtqViEF4vCcwp8aAEm1SXXv1knZ049LQQhhuf2WuLZAu5YGjGXE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770295135; c=relaxed/simple; bh=G9qHb9p0MPYty9W2bqZeDirLOVPesrzx4Ei/lgeOCRA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=c+kXV5O2BfoxgF1NwxuEebv+pbNQSnMebMFhzWiamgYD7fEHYFOjKLr4tZ6hOdw3bGng19MTUTcw0MsQ31TuvaagqIONq6G9QogJKUhxTNc2UpiCgwOR/BJoG9KsTdxodLPHLg0hMdsaO4OLCUxXfoBJO/1Z6FdgDFXMa3akPh4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AH2UzJ0o; 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="AH2UzJ0o" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1042BC4CEF7; Thu, 5 Feb 2026 12:38:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770295135; bh=G9qHb9p0MPYty9W2bqZeDirLOVPesrzx4Ei/lgeOCRA=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=AH2UzJ0oUDVcL390IygZ5kEiEAojgl8odoQ3KAjqbiFXfHBGLmz5bMu51boYaY+VD sAdILXp3eIJngbsv0/hIvYZNP9usrSjIp1vqGT5x51WhcxUN4NOg5i0D92Fkt3onWj Z6k8Lrgcq8NhtRpCBsSkxMklVvogfeWyn2TF89SHArhTOh2myE8CITFFMhH9k5KwgN X3rbQZQpCJfxSEERajtHka8wsvMw1fDk8idcYs7NfRKDwlPKGAjewutiezQm2na7Fr 1vDGRIPsPDHUgCsiVe1GcvsXveA0CuG1G4tTDyYNNGmepDqEYYrKqYrUO40iI0Awe6 +3/gkPxG11tfw== Message-ID: Subject: Re: [PATCH 11/13] ovl: use is_subdir() for testing if one thing is a subdir of another From: Jeff Layton To: NeilBrown , Christian Brauner , Alexander Viro , David Howells , Jan Kara , Chuck Lever , Miklos Szeredi , Amir Goldstein , John Johansen , Paul Moore , James Morris , "Serge E. Hallyn" , Stephen Smalley Cc: linux-kernel@vger.kernel.org, netfs@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-unionfs@vger.kernel.org, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, selinux@vger.kernel.org Date: Thu, 05 Feb 2026 07:38:52 -0500 In-Reply-To: <20260204050726.177283-12-neilb@ownmail.net> References: <20260204050726.177283-1-neilb@ownmail.net> <20260204050726.177283-12-neilb@ownmail.net> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-02-04 at 15:57 +1100, NeilBrown wrote: > From: NeilBrown >=20 > Rather than using lock_rename(), use the more obvious is_subdir() for > ensuring that neither upper nor workdir contain the other. > Also be explicit in the comment that the two directories cannot be the > same. >=20 > As this is a point-it-time sanity check and does not provide any > on-going guarantees, the removal of locking does not introduce any > interesting races. >=20 > Signed-off-by: NeilBrown > --- > fs/overlayfs/super.c | 15 +++++---------- > 1 file changed, 5 insertions(+), 10 deletions(-) >=20 > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c > index ba9146f22a2c..2fd3e0aee50e 100644 > --- a/fs/overlayfs/super.c > +++ b/fs/overlayfs/super.c > @@ -451,18 +451,13 @@ static int ovl_lower_dir(const char *name, const st= ruct path *path, > return 0; > } > =20 > -/* Workdir should not be subdir of upperdir and vice versa */ > +/* > + * Workdir should not be subdir of upperdir and vice versa, and > + * they should not be the same. > + */ > static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperd= ir) > { > - bool ok =3D false; > - > - if (workdir !=3D upperdir) { > - struct dentry *trap =3D lock_rename(workdir, upperdir); > - if (!IS_ERR(trap)) > - unlock_rename(workdir, upperdir); > - ok =3D (trap =3D=3D NULL); > - } > - return ok; > + return !is_subdir(workdir, upperdir) && !is_subdir(upperdir, workdir); > } > =20 > static int ovl_setup_trap(struct super_block *sb, struct dentry *dir, Reviewed-by: Jeff Layton