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Mon, 19 Oct 2026 15:05:05 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id OmfsJqEx1mpmEQAAD6G6ig (envelope-from ); Mon, 19 Oct 2026 15:05:05 +0000 Date: Mon, 19 Oct 2026 17:05:04 +0200 From: David Sterba To: guolingxing Cc: David Sterba , Qu Wenruo , Chris Mason , Marcos Paulo de Souza , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] btrfs: prevent deleting the wrong subvolume by ID Message-ID: <20261019150504.GD1310987@twin.jikos.cz> Reply-To: dsterba@suse.cz References: <20261018073709.1586733-1-guolingxing@tju.edu.cn> <20261018153810.2692021-1-guolingxing@tju.edu.cn> X-Mailing-List: linux-kernel@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: <20261018153810.2692021-1-guolingxing@tju.edu.cn> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Spam-Flag: NO X-Spam-Score: -4.00 X-Spam-Level: X-Spamd-Result: default: False [-4.00 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; HAS_REPLYTO(0.30)[dsterba@suse.cz]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; RCVD_COUNT_TWO(0.00)[2]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; REPLYTO_ADDR_EQ_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:replyto,imap1.dmz-prg2.suse.org:helo,suse.com:email] On Sun, Oct 18, 2026 at 03:38:10PM +0000, guolingxing wrote: > When deleting a subvolume by ID, btrfs_ioctl_snap_destroy() first > resolves the requested ID to a name, then looks up that name again > under the parent directory lock. > > A concurrent rename can change which subvolume is associated with > the name between these operations. Since the deletion path does not > verify the ID of the resolved subvolume, it can delete a different > subvolume while leaving the requested one intact. > > This was reproduced by repeatedly exchanging the names of two > subvolumes using renameat2(RENAME_EXCHANGE) while deleting one of > them by ID. The wrong subvolume was deleted in 9 out of 14 independent > tests. > > Fix this by checking that the resolved subvolume ID matches the > requested ID while holding the parent directory lock. Return -EAGAIN > on a mismatch so that userspace can retry the operation instead of > being told that the requested subvolume does not exist. > > Fixes: 949964c92843 ("btrfs: add new BTRFS_IOC_SNAP_DESTROY_V2 ioctl") > Cc: stable@vger.kernel.org > Signed-off-by: guolingxing > --- > Changes since v1: > - Return -EAGAIN instead of -ENOENT on a subvolume ID mismatch, > as suggested by Qu Wenruo. EAGAIN is a good choice here, usually used for restartable operations, which in this case it is and allows user to see what happened. Reviewed-by: David Sterba