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 X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC6E3C43461 for ; Wed, 19 May 2021 00:51:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3B7F6135D for ; Wed, 19 May 2021 00:51:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233400AbhESAwn (ORCPT ); Tue, 18 May 2021 20:52:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234642AbhESAu5 (ORCPT ); Tue, 18 May 2021 20:50:57 -0400 Received: from zeniv-ca.linux.org.uk (zeniv-ca.linux.org.uk [IPv6:2607:5300:60:148a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDFB6C06175F; Tue, 18 May 2021 17:49:37 -0700 (PDT) Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94 #2 (Red Hat Linux)) id 1ljAOT-00G4FY-K4; Wed, 19 May 2021 00:49:01 +0000 From: Al Viro To: Linus Torvalds Cc: Jia He , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes , Jonathan Corbet , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , "Eric W . Biederman" , "Darrick J. Wong" , "Peter Zijlstra (Intel)" , Ira Weiny , Eric Biggers , "Ahmed S. Darwish" , "open list:DOCUMENTATION" , Linux Kernel Mailing List , linux-s390 , linux-fsdevel Subject: [PATCH 03/14] d_path: regularize handling of root dentry in __dentry_path() Date: Wed, 19 May 2021 00:48:50 +0000 Message-Id: <20210519004901.3829541-3-viro@zeniv.linux.org.uk> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210519004901.3829541-1-viro@zeniv.linux.org.uk> References: <20210519004901.3829541-1-viro@zeniv.linux.org.uk> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org All path-forming primitives boil down to sequence of prepend_name() on dentries encountered along the way toward root. Each time we prepend / + dentry name to the buffer. Normally that does exactly what we want, but there's a corner case when we don't call prepend_name() at all (in case of __dentry_path() that happens if we are given root dentry). We obviously want to end up with "/", rather than "", so this corner case needs to be handled. __dentry_path() used to manually put '/' in the end of buffer before doing anything else, to be overwritten by the first call of prepend_name() if one happens and to be left in place if we don't call prepend_name() at all. That required manually checking that we had space in the buffer (prepend_name() and prepend() take care of such checks themselves) and lead to clumsy keeping track of return value. A better approach is to check if the main loop has added anything into the buffer and prepend "/" if it hasn't. A side benefit of using prepend() is that it does the right thing if we'd already run out of buffer, making the overflow-handling logics simpler. Signed-off-by: Al Viro --- fs/d_path.c | 21 +++++---------------- 1 file changed, 5 insertions(+), 16 deletions(-) diff --git a/fs/d_path.c b/fs/d_path.c index 1a1cf05e7780..b3324ae7cfe2 100644 --- a/fs/d_path.c +++ b/fs/d_path.c @@ -329,31 +329,22 @@ char *simple_dname(struct dentry *dentry, char *buffer, int buflen) static char *__dentry_path(const struct dentry *d, char *p, int buflen) { const struct dentry *dentry; - char *end, *retval; + char *end; int len, seq = 0; - int error = 0; - - if (buflen < 1) - goto Elong; rcu_read_lock(); restart: dentry = d; end = p; len = buflen; - /* Get '/' right */ - retval = end-1; - *retval = '/'; read_seqbegin_or_lock(&rename_lock, &seq); while (!IS_ROOT(dentry)) { const struct dentry *parent = dentry->d_parent; prefetch(parent); - error = prepend_name(&end, &len, &dentry->d_name); - if (error) + if (unlikely(prepend_name(&end, &len, &dentry->d_name) < 0)) break; - retval = end; dentry = parent; } if (!(seq & 1)) @@ -363,11 +354,9 @@ static char *__dentry_path(const struct dentry *d, char *p, int buflen) goto restart; } done_seqretry(&rename_lock, seq); - if (error) - goto Elong; - return retval; -Elong: - return ERR_PTR(-ENAMETOOLONG); + if (len == buflen) + prepend(&end, &len, "/", 1); + return len >= 0 ? end : ERR_PTR(-ENAMETOOLONG); } char *dentry_path_raw(const struct dentry *dentry, char *buf, int buflen) -- 2.11.0