From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.208.53 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794305680; b=uPWvbxiE0t8mIg0poyMaQmZC1YfZzhK/n3mHUcr+JTtboZFGvV/sAQiSNScUetH8lw/R fcvqP85clli79xqmIa36LFFp+0nqFVcd41mkeM5fuF1xFFIpCFjrB95Q88nCoeIjo+mOp OCzMNxFuS3AiA+2qlj84OvLtAtg6+zbHdaS1N0pr/kpa4998RW0l93U5uT+eeH72YoOIi KqnyJnqkaGJ4u0Mtd2IEpFR4mJMevMDJ3KKCoGPVOzPZSKvGwAZXARv2jpiv8dQgMpNbL 0XX2Vlf0pJ1esKVL3iRhyep/8cepoO5o/3oFJaQWcLvuz8DFvVh6YY2AaMVB+2hI8pA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794305680; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; bh=9WFltYRvNkpM0HMxRLJxGiCTEiP83WtKPHu+oXy3KTg=; b=1edeftwlXxh7pFBMAkCMZ1qYBX0pR0D0fCzhCmZMxI908BUnJ9z7YQ+oS4rEPWTYweow Fd0Iy+POZ0OKwH3MK2KdDUvED4HpAVlSVfk20g9uXG0IkTDvJW1hFhgb7s2dIPMmXVYS9 S59mdr66micnhJlQe51h+gzvBCj1DVL2eQGU+fXmKUDW5lWaFszwZCQzUkuaxilE/F2dP xPYCoNmKb9q2C3xRomYo1q+MGe8RJv5TRlxV5uJd0TyceOMmAZcqvqoXxt1CKfXCxnM/d 6wp6UgfEOlFYovdanPPOusHUkvSGRFz4azTbQDr35o4xWYkgqtP17fjyeqTmJsue6nA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=DrlQYRb4; arc=none smtp.remote-ip=209.85.208.53 Received: from mail-ed1-f53.google.com (mail-ed1-f53.google.com [209.85.208.53]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E7C9D606A335 for ; Tue, 10 Nov 2026 10:14:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org E7C9D606A335 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=DrlQYRb4 Received: by mail-ed1-f53.google.com with SMTP id 4fb4d7f45d1cf-6b5973a4b4cso2116650a12.2 for ; Tue, 10 Nov 2026 02:14:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1794305678; x=1794910478; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=9WFltYRvNkpM0HMxRLJxGiCTEiP83WtKPHu+oXy3KTg=; b=DrlQYRb4d+FJBQLFk4gip1vdMb9pZcbFm0QRoW/O9nsnnIGk5B/dcI7komCKzkv/uM Uz0TTkL3EB0XOLA2v0TTxwYvqDOvah1wiwbB4uUsiRRXfj1OcdvtnHWnMQS6yfKTNN5Y 2S+sbZpFj/oUd6OIfB1K+t4luOgmpm8MRta8dNUBz+XdEb16ui6jztHrAySR2QYDDBtW UcH7ksMk3kyTCuhLg24n4RSbgP43bR1MD63YWBBHbNHKba+s6Adtgd3r0iiTavTYgvkx vCBmyxhjfzRfUpjuhY0K7x1CK/3uUIf/0FzbTbFW5bHu/k5G1xko0Cr6O3LrrObY61iA y+ww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1794305678; x=1794910478; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=9WFltYRvNkpM0HMxRLJxGiCTEiP83WtKPHu+oXy3KTg=; b=KmEC04kKvIrCJeC7CLbsSFYUK0wMtDLF2+RVG6PolIN0BzNSNfNobAnN4ykqQynGzQ zjJdP2DNKoCZ4UHCuDKYWFRDmsXep4uhsLdc3lWQltm86E7lNkZrP1YRm71qks/zkc7F zvnDo4Av+KM5OI3yPrq4KHGj37Ago+XelNjuUqdX5v0kC5GmmPlf2ekAR+ehbS0kdiiw BAtxkZxlI5T7Hh+7JCzPdnlsQt4EAEChZJeBh/L/p1jwNr2jOSFTyEZmUshQ5Aw1ImSn PFH85E6gHYLDrp0lYe1UYCW4curaXmZYWTZIyTBciU8ckWiquvRt5WCZFUzrwQITSAk9 1ZKg== X-Forwarded-Encrypted: i=1; AL+hErGJA8r+upegqHREAx4TjXyhx7yR6KF4PwWAwaPzVNam+jgBVP1dDB4zoLPh4Evqx7U9uMjczpK4q/VmJZb3+JhzlxT/fkU=@vger.kernel.org X-Gm-Message-State: APuU4Z9RqZe65lCVEd5SWoamyWt0BDhBCev1BaR7sZQZMk5NSfRE3GVB 5vFp91/6JVieOuuSigYFC4HpVnu89qeBns83UL60zrIKXV7t9usiNkSK X-Gm-Gg: AYBFou0WHABFgQZ1Vd/AhV4y9FfAEOH+AadZmZxmBJc/5Us9FTOQil3JSE6iKI4lZb5 TkDsGD+ETLJybBrECwfvfl+Ziq3+sq5sRKXN8QvlI9BhZtwTtUtA/Wo+dzw80mBCfA0OPsO3b/y 16/9BhdWjehlwNcFZYuKrWAKzmdL3TY5R2sqEWrFbRjopqrXW9pvy+mbk0jLLWivkWtyuTtgwJB 7IsPYSerXs7dIYVrY2zIfUcG85eq2DbjQTZvjyOv7e/2q4pYBFettmCEkQFC9fcr2tdDhyJfoal /w1M0w3nPtM1nZtNZAFeHlPyDWrqd/5aH+m4Or8ZVJGE5CkWpGctUJGr+9lcek8hmWWNLEDwkzP 59WyLwaJm2HbexPG53ZiegA8WAVNmfHmyB6TvZiEJKI1UFe73cwshDOwnMQ0z8+zs4h5r7oI67l +ciX6KDfB1M6u16jrQuczzbR02WsTuOnYMkZM29UKmd/FaSlhzjrrcagVHGe+Q0tZyJgljmm9kO AlYV/aZ1AWeQguKJORBaSTWuonRYZ0tWtkpeOa+388CmqFAlKY4ZH1MERhGQM5zUI4Cr0l+NYvb S+hg7wL4/wXJsDaID9QSqYvrWb/xaAOFAvKvPOpViDIYQFXW7bJ2Pg40UY0j1hjb6FF36tHSray ZsZ3OBbeQKKOb X-Received: by 2002:a17:907:944d:b0:c41:4c20:5a80 with SMTP id a640c23a62f3a-c504963ce05mr189793966b.44.1794305677695; Tue, 10 Nov 2026 02:14:37 -0800 (PST) Received: from localhost (178-84-201-199.dynamic.upc.nl. [178.84.201.199]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c504a593eacsm90433466b.36.2026.11.10.02.14.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Nov 2026 02:14:36 -0800 (PST) Date: Tue, 10 Nov 2026 11:14:35 +0100 From: Amir Goldstein To: Christian Brauner Cc: linux-fsdevel@vger.kernel.org, Jann Horn , Chris Mason , Josef Bacik , Christoph Hellwig , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, Alexander Viro , Jan Kara , linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, driver-core@lists.linux.dev, linux-mm@kvack.org, bpf@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, apparmor@lists.ubuntu.com, linux-nfs@vger.kernel.org, netdev@vger.kernel.org, fuse-devel@lists.linux.dev, linux-efi@vger.kernel.org, xen-devel@lists.xenproject.org, ocfs2-devel@lists.linux.dev, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-usb@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC 38/41] fuse: refuse files on pseudo filesystems as passthrough backing files Message-ID: References: <20261110-work-loop-pseudo-v1-0-4c998976c6c7@kernel.org> <20261110-work-loop-pseudo-v1-38-4c998976c6c7@kernel.org> X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261110-work-loop-pseudo-v1-38-4c998976c6c7@kernel.org> On Tue, Nov 10, 2026 at 10:14:54AM +0100, Christian Brauner wrote: > The fuse server can register any regular file as a backing file. procfs > and binfmt_misc files are already refused by the stacking depth check as > both set s_stack_depth to FILESYSTEM_MAX_STACK_DEPTH. sysfs and the > other pseudo filesystems aren't. Reads and writes of the fuse file would > then be done on the pseudo file with the fuse server's credentials. > Refuse files on pseudo filesystems just like loop does. > > Signed-off-by: Christian Brauner (Amutable) > --- > fs/fuse/backing.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c > index 8c21a8a74efb..4e4fb810ddaa 100644 > --- a/fs/fuse/backing.c > +++ b/fs/fuse/backing.c > @@ -147,6 +147,9 @@ static int fuse_backing_open_file(struct fuse_conn *fc, struct fuse_backing *fb, > if (inode->i_sb->s_stack_depth >= fc->max_stack_depth) > return -ELOOP; > > + if (file_is_pseudo(file)) > + return -EINVAL; > + > fb->type = FUSE_BACKING_PATH; > fb->path = file->f_path; > path_get(&fb->path); > > -- > 2.53.0 > Reviewed-by: Amir Goldstein