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[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-Archived-By: 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> X-Rspamd-Queue-Id: 9D12E40003 X-Rspamd-Server: rspam12 X-Stat-Signature: 71xwcorjfkc3yjsinouzc3w3wt9n1pk1 X-Rspam-User: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794305679-767070 X-HE-Meta: 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 ltx4LdML 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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