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=-8.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham 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 1BA07C65BAE for ; Thu, 13 Dec 2018 06:58:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB5A32080F for ; Thu, 13 Dec 2018 06:58:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB5A32080F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726947AbeLMG6i (ORCPT ); Thu, 13 Dec 2018 01:58:38 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:40516 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726542AbeLMG6h (ORCPT ); Thu, 13 Dec 2018 01:58:37 -0500 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.91 #2 (Red Hat Linux)) id 1gXKx0-0006KL-8m; Thu, 13 Dec 2018 06:58:26 +0000 Date: Thu, 13 Dec 2018 06:58:26 +0000 From: Al Viro To: Ivan Delalande Cc: Luis Chamberlain , Kees Cook , Andrew Morton , "Eric W. Biederman" , Alexey Dobriyan , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] proc/sysctl: don't return ENOMEM on lookup when a table is unregistering Message-ID: <20181213065826.GL2217@ZenIV.linux.org.uk> References: <20181213015742.GA28776@visor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181213015742.GA28776@visor> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 12, 2018 at 05:57:43PM -0800, Ivan Delalande wrote: > proc_sys_lookup can fail with ENOMEM instead of ENOENT when the > corresponding sysctl table is being unregistered. In our case we see > this upon opening /proc/sys/net/*/conf files while network interfaces > are being removed, which confuses our configuration daemon. > > The problem was successfully reproduced and this fix tested on v4.9.122 > and v4.20-rc6. > > Fixes: ace0c791e6c3 ("proc/sysctl: Don't grab i_lock under sysctl_lock.") > Cc: stable@vger.kernel.org > Signed-off-by: Ivan Delalande > --- > fs/proc/proc_sysctl.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c > index 89921a0d2ebb..834be5bc3d07 100644 > --- a/fs/proc/proc_sysctl.c > +++ b/fs/proc/proc_sysctl.c > @@ -474,7 +474,7 @@ static struct inode *proc_sys_make_inode(struct super_block *sb, > if (unlikely(head->unregistering)) { > spin_unlock(&sysctl_lock); > iput(inode); > - inode = NULL; > + inode = ERR_PTR(-ENOENT); > goto out; > } > ei->sysctl = head; > @@ -549,10 +549,11 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry, > goto out; > } > > - err = ERR_PTR(-ENOMEM); > inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p); > - if (!inode) > + if (IS_ERR_OR_NULL(inode)) { > + err = inode ? ERR_CAST(inode) : ERR_PTR(-ENOMEM); *gags* If you want to return specific errors, do just that and for pity sake, do *NOT* invent such hybrids. "Pointer to object on success, ERR_PTR(-E...) on failure, NULL means ERR_PTR(-ENOMEM)" is a bitch to reason about and prone to breakage. "Return NULL on error" and "return ERR_PTR() on error" do not mix. Just make proc_sys_make_inode() return ERR_PTR(-ENOMEM) on allocation failures and update the callers (as you have to, anyway). IS_ERR_OR_NULL() is usually a sign of bad calling conventions and it certainly is just that in this case. Just do inode = new_inode(sb); if (!inode) return ERR_PTR(-ENOMEM); in there, in addition to your return of ERR_PTR(-ENOENT), and lose those IS_ERR_OR_NULL() things. Make those IS_ERR() and turn the assignment to err into straight ERR_CAST(). All there is to it...