From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8DFC0C41513 for ; Mon, 14 Aug 2023 14:51:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230497AbjHNOul (ORCPT ); Mon, 14 Aug 2023 10:50:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232574AbjHNOuV (ORCPT ); Mon, 14 Aug 2023 10:50:21 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A041A10E3; Mon, 14 Aug 2023 07:50:16 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 556941FD60; Mon, 14 Aug 2023 14:50:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1692024615; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=B6QIsNcUwY8iaBQqkPm5CJUyjIlEcOaJL8XUAsTGurs=; b=d0ip1fpopDbZZIpEG2n3ugzEJDCgNjtoWycFPUrAgciZqLVQXjz5vH9T/jrLsIVIpoCg0w D4JrQl8IX/TT6mKO6w11eu6jZgcP39M/xI2ZdgkATpnKJEFFwNIdLqmRn+Yu61RA5PBVsA qSWnEpZ4P+rDioQqbjMVhBdJBGy1Pso= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1692024615; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=B6QIsNcUwY8iaBQqkPm5CJUyjIlEcOaJL8XUAsTGurs=; b=EMCLmF8DPJ4gucLOmtGbdPWovgTA592tSqk9udFjlxy6BE/iRLBkhKYf01o3XmDnF04e8h qOFz+0n8e9NifWCA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 01810138EE; Mon, 14 Aug 2023 14:50:14 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id AG+pMCY/2mT+BQAAMHmgww (envelope-from ); Mon, 14 Aug 2023 14:50:14 +0000 From: Gabriel Krisman Bertazi To: Eric Biggers Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, tytso@mit.edu, jaegeuk@kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Gabriel Krisman Bertazi Subject: Re: [PATCH v5 06/10] libfs: Validate negative dentries in case-insensitive directories In-Reply-To: <20230812024145.GD971@sol.localdomain> (Eric Biggers's message of "Fri, 11 Aug 2023 19:41:45 -0700") Organization: SUSE References: <20230812004146.30980-1-krisman@suse.de> <20230812004146.30980-7-krisman@suse.de> <20230812024145.GD971@sol.localdomain> Date: Mon, 14 Aug 2023 10:50:13 -0400 Message-ID: <87a5ut7k62.fsf@suse.de> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org Eric Biggers writes: > On Fri, Aug 11, 2023 at 08:41:42PM -0400, Gabriel Krisman Bertazi wrote: >> + /* >> + * Filesystems will call into d_revalidate without setting >> + * LOOKUP_ flags even for file creation (see lookup_one* >> + * variants). Reject negative dentries in this case, since we >> + * can't know for sure it won't be used for creation. >> + */ >> + if (!flags) >> + return 0; >> + >> + /* >> + * If the lookup is for creation, then a negative dentry can >> + * only be reused if it's a case-sensitive match, not just a >> + * case-insensitive one. This is needed to make the new file be >> + * created with the name the user specified, preserving case. >> + */ >> + if (flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET)) { >> + /* >> + * ->d_name won't change from under us in the creation >> + * path only, since d_revalidate during creation and >> + * renames is always called with the parent inode >> + * locked. It isn't the case for all lookup callpaths, >> + * so ->d_name must not be touched outside >> + * (LOOKUP_CREATE|LOOKUP_RENAME_TARGET) context. >> + */ >> + if (dentry->d_name.len != name->len || >> + memcmp(dentry->d_name.name, name->name, name->len)) >> + return 0; >> + } > > This is still really confusing to me. Can you consider the below? The code is > the same except for the reordering, but the explanation is reworked to be much > clearer (IMO). Anything I am misunderstanding? > > /* > * If the lookup is for creation, then a negative dentry can only be > * reused if it's a case-sensitive match, not just a case-insensitive > * one. This is needed to make the new file be created with the name > * the user specified, preserving case. > * > * LOOKUP_CREATE or LOOKUP_RENAME_TARGET cover most creations. In these > * cases, ->d_name is stable and can be compared to 'name' without > * taking ->d_lock because the caller holds dir->i_rwsem for write. > * (This is because the directory lock blocks the dentry from being > * concurrently instantiated, and negative dentries are never moved.) > * > * All other creations actually use flags==0. These come from the edge > * case of filesystems calling functions like lookup_one() that do a > * lookup without setting the lookup flags at all. Such lookups might > * or might not be for creation, and if not don't guarantee stable > * ->d_name. Therefore, invalidate all negative dentries when flags==0. > */ > if (flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET)) { > if (dentry->d_name.len != name->len || > memcmp(dentry->d_name.name, name->name, name->len)) > return 0; > } > if (!flags) > return 0; I don't see it as particularly better or less confusing than the original. but I also don't mind taking it into the next iteration. -- Gabriel Krisman Bertazi