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=-9.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 3EA6CC282C2 for ; Wed, 23 Jan 2019 11:06:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2DE421019 for ; Wed, 23 Jan 2019 11:06:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548241594; bh=1feXq55a+tjAd8GPP3+j0e4i97UqMAOmFaFkijc0wTM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=UdD9ODaZWsP6Mz9mZGNCj5PxbcoalN07tPJDqHe5YjOK2d4nNYavynikUqgAihmtQ 9TbllYftAIKO3oKlYR74rwTpEnunuqz1085ig0XeBmcpUFwC+wd3IM837eHpSEBRUz D3hMLvwupZkRv1C/pXGNi3cpHhagOEpZ6KroThNc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727430AbfAWLGc (ORCPT ); Wed, 23 Jan 2019 06:06:32 -0500 Received: from mx2.suse.de ([195.135.220.15]:55480 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726207AbfAWLGc (ORCPT ); Wed, 23 Jan 2019 06:06:32 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 2257FAF4F; Wed, 23 Jan 2019 11:06:30 +0000 (UTC) Date: Wed, 23 Jan 2019 12:06:28 +0100 From: Michal Hocko To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, Masami Hiramatsu , Ulf Hansson , Gary R Hook , Heiko Carstens Subject: Re: [PATCH 2/2] debugfs: return error values, not NULL Message-ID: <20190123110628.GV4087@dhcp22.suse.cz> References: <20190123102702.GA17123@kroah.com> <20190123102814.GB17123@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190123102814.GB17123@kroah.com> 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 23-01-19 11:28:14, Greg KH wrote: > When an error happens, debugfs should return an error pointer value, not > NULL. This will prevent the totally theoretical error where a debugfs > call fails due to lack of memory, returning NULL, and that dentry value > is then passed to another debugfs call, which would end up succeeding, > creating a file at the root of the debugfs tree, but would then be > impossible to remove (because you can not remove the directory NULL). > > So, to make everyone happy, always return errors, this makes the users > of debugfs much simpler (they do not have to ever check the return > value), and everyone can rest easy. How come this is safe at all? Say you are creating a directory by debugfs_create_dir and then feed the return value to debugfs_create_files as a parent. In case of error you are giving it an invalid pointer and likely blow up unless I miss something. I do agree that reporting errors is better than a simple catch all NULL but this should have been done when introduced rather than now when most callers simply check for NULL as a failure. > Reported-by: Masami Hiramatsu > Reported-by: Ulf Hansson > Reported-by: Gary R Hook > Reported-by: Heiko Carstens > Cc: stable > Signed-off-by: Greg Kroah-Hartman > --- > fs/debugfs/inode.c | 39 ++++++++++++++++++++++----------------- > 1 file changed, 22 insertions(+), 17 deletions(-) > > diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c > index 41ef452c1fcf..b16f8035b1af 100644 > --- a/fs/debugfs/inode.c > +++ b/fs/debugfs/inode.c > @@ -254,8 +254,8 @@ MODULE_ALIAS_FS("debugfs"); > * @parent: a pointer to the parent dentry of the file. > * > * This function will return a pointer to a dentry if it succeeds. If the file > - * doesn't exist or an error occurs, %NULL will be returned. The returned > - * dentry must be passed to dput() when it is no longer needed. > + * doesn't exist or an error occurs, %ERR_PTR(-ERROR) will be returned. The > + * returned dentry must be passed to dput() when it is no longer needed. > * > * If debugfs is not enabled in the kernel, the value -%ENODEV will be > * returned. > @@ -265,17 +265,17 @@ struct dentry *debugfs_lookup(const char *name, struct dentry *parent) > struct dentry *dentry; > > if (IS_ERR(parent)) > - return NULL; > + return parent; > > if (!parent) > parent = debugfs_mount->mnt_root; > > dentry = lookup_one_len_unlocked(name, parent, strlen(name)); > if (IS_ERR(dentry)) > - return NULL; > + return dentry; > if (!d_really_is_positive(dentry)) { > dput(dentry); > - return NULL; > + return ERR_PTR(-EINVAL); > } > return dentry; > } > @@ -324,7 +324,7 @@ static struct dentry *failed_creating(struct dentry *dentry) > inode_unlock(d_inode(dentry->d_parent)); > dput(dentry); > simple_release_fs(&debugfs_mount, &debugfs_mount_count); > - return NULL; > + return ERR_PTR(-ENOMEM); > } > > static struct dentry *end_creating(struct dentry *dentry) > @@ -347,7 +347,7 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode, > dentry = start_creating(name, parent); > > if (IS_ERR(dentry)) > - return NULL; > + return dentry; > > inode = debugfs_get_inode(dentry->d_sb); > if (unlikely(!inode)) > @@ -386,7 +386,8 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode, > * This function will return a pointer to a dentry if it succeeds. This > * pointer must be passed to the debugfs_remove() function when the file is > * to be removed (no automatic cleanup happens if your module is unloaded, > - * you are responsible here.) If an error occurs, %NULL will be returned. > + * you are responsible here.) If an error occurs, %ERR_PTR(-ERROR) will be > + * returned. > * > * If debugfs is not enabled in the kernel, the value -%ENODEV will be > * returned. > @@ -464,7 +465,8 @@ EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe); > * This function will return a pointer to a dentry if it succeeds. This > * pointer must be passed to the debugfs_remove() function when the file is > * to be removed (no automatic cleanup happens if your module is unloaded, > - * you are responsible here.) If an error occurs, %NULL will be returned. > + * you are responsible here.) If an error occurs, %ERR_PTR(-ERROR) will be > + * returned. > * > * If debugfs is not enabled in the kernel, the value -%ENODEV will be > * returned. > @@ -495,7 +497,8 @@ EXPORT_SYMBOL_GPL(debugfs_create_file_size); > * This function will return a pointer to a dentry if it succeeds. This > * pointer must be passed to the debugfs_remove() function when the file is > * to be removed (no automatic cleanup happens if your module is unloaded, > - * you are responsible here.) If an error occurs, %NULL will be returned. > + * you are responsible here.) If an error occurs, %ERR_PTR(-ERROR) will be > + * returned. > * > * If debugfs is not enabled in the kernel, the value -%ENODEV will be > * returned. > @@ -506,7 +509,7 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent) > struct inode *inode; > > if (IS_ERR(dentry)) > - return NULL; > + return dentry; > > inode = debugfs_get_inode(dentry->d_sb); > if (unlikely(!inode)) > @@ -545,7 +548,7 @@ struct dentry *debugfs_create_automount(const char *name, > struct inode *inode; > > if (IS_ERR(dentry)) > - return NULL; > + return dentry; > > inode = debugfs_get_inode(dentry->d_sb); > if (unlikely(!inode)) > @@ -581,8 +584,8 @@ EXPORT_SYMBOL(debugfs_create_automount); > * This function will return a pointer to a dentry if it succeeds. This > * pointer must be passed to the debugfs_remove() function when the symbolic > * link is to be removed (no automatic cleanup happens if your module is > - * unloaded, you are responsible here.) If an error occurs, %NULL will be > - * returned. > + * unloaded, you are responsible here.) If an error occurs, %ERR_PTR(-ERROR) > + * will be returned. > * > * If debugfs is not enabled in the kernel, the value -%ENODEV will be > * returned. > @@ -594,12 +597,12 @@ struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent, > struct inode *inode; > char *link = kstrdup(target, GFP_KERNEL); > if (!link) > - return NULL; > + return ERR_PTR(-ENOMEM); > > dentry = start_creating(name, parent); > if (IS_ERR(dentry)) { > kfree(link); > - return NULL; > + return dentry; > } > > inode = debugfs_get_inode(dentry->d_sb); > @@ -827,7 +830,9 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry, > if (dentry && !IS_ERR(dentry)) > dput(dentry); > unlock_rename(new_dir, old_dir); > - return NULL; > + if (IS_ERR(dentry)) > + return dentry; > + return ERR_PTR(-EINVAL); > } > EXPORT_SYMBOL_GPL(debugfs_rename); > > -- > 2.20.1 -- Michal Hocko SUSE Labs