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Wong" , Miklos Szeredi , linux-fsdevel@vger.kernel.org, Joanne Koong , John Groves , Bernd Schubert , Amir Goldstein , Luis Henriques , Horst Birthelmer , Gao Xiang , lsf-pc@lists.linux-foundation.org Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Where is fuse going? API cleanup, restructuring and more Message-ID: References: <20260221004752.GE11076@frogsfrogsfrogs> <7de8630d-b6f5-406e-809a-bc2a2d945afb@linux.alibaba.com> <20260318215140.GL1742010@frogsfrogsfrogs> <361d312b-9706-45ca-8943-b655a75c765b@gmail.com> <390cd031-742b-4f1b-99c4-8ee41a259744@linux.alibaba.com> <72eaaed1-24a0-4c98-a7c0-ea249d541f2d@linux.alibaba.com> <9af9ad0e-8070-4aaa-9f64-7d72074bd948@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9af9ad0e-8070-4aaa-9f64-7d72074bd948@linux.alibaba.com> X-Spamd-Result: default: False [-4.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; RCVD_COUNT_THREE(0.00)[3]; URIBL_BLOCKED(0.00)[suse.cz:dkim,suse.com:email,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[14]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TO_DN_SOME(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:dkim,suse.com:email,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_TLS_LAST(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; MISSING_XM_UA(0.00)[]; FREEMAIL_CC(0.00)[suse.cz,gmail.com,kernel.org,szeredi.hu,vger.kernel.org,groves.net,bsbernd.com,igalia.com,birthelmer.de,lists.linux-foundation.org]; SUBJECT_HAS_QUESTION(0.00)[] X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Score: -4.01 X-Spam-Level: X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: A28DC5BCDF On Mon 23-03-26 20:01:32, Gao Xiang wrote: > On 2026/3/23 19:42, Gao Xiang wrote: > > > for example, you could audit the file permission with > > e2fsprogs/xfsprogs without a full fsck scan. > > > > In order to make the userspace programs best-effort, they > > should open for write and fstat the permission bits > > before writing sensitive informations, it avoids TOCTOU > > attacks as much as possible as userspace programs. > > > > > > Container users use namespaces of course, namespace can > > only provide isolations, that is the only security > > guarantees namespace can provide, no question of that. > > > > Let's just strictly speaking, as you mentioned, both ways > > ensure the isolation (if namespaces are used) and kernel > > stability (let's not nitpick about this).  And let's not > > talk about malicious block devices or likewise, because > > it's not a typical setup (maybe it could be a typical > > setup for some cases, but it should be another system-wide > > security design) and should be clarified by system admins > > for example. > > > > What I just want to say is that: FUSE mount approach _might_ > > give more incorrect security guarantees than the real users > > expect: I think other than avoiding system crashes etc, many > > users should expect that they could use the generic writable > > filesystem directly with FUSE without full-scan fsck > > in advance and keep their sensitive data directly, I don't > > > If you think that is still the corner cases that users expect > incorrectly, For example, I think double freeing issues can > make any useful write stuffs lost just out of inconsistent > filesystem -- that may be totally unrelated to the security. > > What I want to say is that, the users' interest of new FUSE > approch is "no full fsck"; Otherwise, if full fsck is used, > why not they mount in the kernel then (I do think kernel > filesystems should fix all bugs out of normal consistent > usage)? > > However, "no fsck" and FUSE mounts bring many incorrect > assumption that users can never expect: it's still unreliable, > maybe cannot keep any useful data in that storage. > > Hopefully I explain my idea. I see and I agree that for some cases FUSE access to the untrusted filesystem needn't be enough > > think that is the corner cases if you don't claim the > > limitation of FUSE approaches. > > > > If none expects that, that is absolute be fine, as I said, > > it provides strong isolation and stability, but I really > > suspect this approach could be abused to mount totally > > untrusted remote filesystems (Actually as I said, some > > business of ours already did: fetching EXT4 filesystems > > with unknown status and mount without fscking, that is > > really disappointing.) Yes, someone downloading untrusted ext4 image, mounting in read-write and using it for sensitive application, that falls to "insane" category for me :) We agree on that. And I agree that depending on the application using FUSE to access such filesystem needn't be safe enough and immutable fs + overlayfs writeable layer may provide better guarantees about fs behavior. I would still consider such design highly suspicious but without more detailed knowledge about the application I cannot say it's outright broken :). Honza -- Jan Kara SUSE Labs, CR