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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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261110_021440_235177_5DD49A24 X-CRM114-Status: GOOD ( 19.38 ) X-Spam-Score: -2.1 (--) X-Mailman-Approved-At: Wed, 11 Nov 2026 13:17:03 -0800 X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 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