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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C9FBC433F5 for ; Thu, 28 Oct 2021 10:39:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 19EE4610D2 for ; Thu, 28 Oct 2021 10:39:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230100AbhJ1KmW (ORCPT ); Thu, 28 Oct 2021 06:42:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:44308 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229775AbhJ1KmV (ORCPT ); Thu, 28 Oct 2021 06:42:21 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2607560296; Thu, 28 Oct 2021 10:39:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1635417594; bh=epjA4bOi3Sjz1EjfLxkcfhOD6RWiQGylAdLkk168yjE=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=KQUvorfuLNZn2YoO3IE4dCWiZLfYOdoLiMGEFcJ+R/rdKVS1tC4fo42BPsnWxbyFh XTzu9vFInZSK27Ur7BXjSfl3JKrMRYB0kwcgrmU8yFWNaeblv8yDAFOlSiX0HhO5qf 5JYKXYWVJ5AByuPtFl8YsyKjX2t5iNj4icAa88croVrmCCR+bw1OD3izv6Nd+r2kUf b5pcVrB9vZsWWUoCo1hFsz5QjyksFt9PtSpARswc/sf1ICEIQqiV5+McUUKynEXeny Y2P0RPTYtKHbIaJSw14Tdn9HBpC9nOfr9lyDrtKNU3OBU5CP3cUyN2xh+OUZKvZexD KanL+/Ftf4chw== Message-ID: Subject: Re: [PATCH] fscache: fix GPF in fscache_free_cookie From: Jeff Layton To: Dongliang Mu Cc: David Howells , linux-cachefs@redhat.com, linux-kernel Date: Thu, 28 Oct 2021 06:39:53 -0400 In-Reply-To: References: <20211027150732.4158273-1-mudongliangabcd@gmail.com> Content-Type: text/plain; charset="ISO-8859-15" User-Agent: Evolution 3.40.4 (3.40.4-2.fc34) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2021-10-28 at 10:20 +0800, Dongliang Mu wrote: > On Wed, Oct 27, 2021 at 11:16 PM Jeff Layton wrote: > > > > On Wed, 2021-10-27 at 23:07 +0800, Dongliang Mu wrote: > > > If fscache_alloc_cookie encounters memory allocation failure, it will > > > go to nomem label and invoke fscache_free_cookie. However, > > > fscache_alloc_cookie assumes current cookie is already linked into > > > fscache_cookies and directly calls list_del. This assumption does not > > > hold since list_add is not called in the above scenario. As a result, it > > > will lead to Null Pointer Dereference. The stack trace is in the > > > following. > > > > > > Call Trace: > > > __list_del_entry include/linux/list.h:132 [inline] > > > list_del include/linux/list.h:146 [inline] > > > fscache_free_cookie fs/fscache/cookie.c:71 [inline] > > > fscache_free_cookie+0x3f/0x100 fs/fscache/cookie.c:66 > > > fscache_alloc_cookie+0x2e2/0x300 fs/fscache/cookie.c:195 > > > __fscache_acquire_cookie fs/fscache/cookie.c:296 [inline] > > > __fscache_acquire_cookie+0x132/0x380 fs/fscache/cookie.c:257 > > > fscache_acquire_cookie include/linux/fscache.h:334 [inline] > > > v9fs_cache_session_get_cookie+0x74/0x120 fs/9p/cache.c:60 > > > v9fs_session_init+0x724/0xa90 fs/9p/v9fs.c:471 > > > v9fs_mount+0x56/0x450 fs/9p/vfs_super.c:126 > > > legacy_get_tree+0x2b/0x90 fs/fs_context.c:610 > > > vfs_get_tree+0x28/0x100 fs/super.c:1498 > > > do_new_mount fs/namespace.c:2988 [inline] > > > path_mount+0xb92/0xfe0 fs/namespace.c:3318 > > > do_mount+0xa1/0xc0 fs/namespace.c:3331 > > > __do_sys_mount fs/namespace.c:3539 [inline] > > > __se_sys_mount fs/namespace.c:3516 [inline] > > > __x64_sys_mount+0xf4/0x160 fs/namespace.c:3516 > > > > > > Fix this by moving the list_add_tail before goto statements. > > > > > > Fixes: 884a76881fc5 ("fscache: Procfile to display cookies") > > > Signed-off-by: Dongliang Mu > > > --- > > > fs/fscache/cookie.c | 8 +++++--- > > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > > > diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c > > > index cd42be646ed3..d101e212db74 100644 > > > --- a/fs/fscache/cookie.c > > > +++ b/fs/fscache/cookie.c > > > @@ -150,6 +150,11 @@ struct fscache_cookie *fscache_alloc_cookie( > > > if (!cookie) > > > return NULL; > > > > > > + /* move list_add_tail before any error handling code */ > > > + write_lock(&fscache_cookies_lock); > > > + list_add_tail(&cookie->proc_link, &fscache_cookies); > > > + write_unlock(&fscache_cookies_lock); > > > + > > > cookie->key_len = index_key_len; > > > cookie->aux_len = aux_data_len; > > > > > > @@ -186,9 +191,6 @@ struct fscache_cookie *fscache_alloc_cookie( > > > * told it may not wait */ > > > INIT_RADIX_TREE(&cookie->stores, GFP_NOFS & ~__GFP_DIRECT_RECLAIM); > > > > > > - write_lock(&fscache_cookies_lock); > > > - list_add_tail(&cookie->proc_link, &fscache_cookies); > > > - write_unlock(&fscache_cookies_lock); > > > return cookie; > > > > > > nomem: > > > > Nice catch! > > > > Reviewed-by: Jeff Layton > > Hi Jeff, > > fscache_free_cookie also has an issue in cookie->backing_objects, but > it does not affect the execution. The reason is in the following: > > At first, I observed that the cookie->backing_objects in > fscache_alloc_cookie is not initialized with INIT_HLIST_HEAD when an > error occurs. It may lead to some issues in the fscache_free_cookie, > e.g., WARN_ON. > > Actually, it does not due to the zero initialization of > kmem_cache_zalloc before. cookie->backing_objects is already with two > null pointers. It does not need INIT_HLIST_HEAD. > > And in the fscache_free_cookie, it actually does not trigger > WARN_ON(!hlist_empty()). > > So I wonder if we need to explicitly move INIT_HLIST_HEAD before any > error handling code. > > I don't think so. INIT_HLIST_HEAD just does this: #define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL) ...so I think it's unnecessary in this case, since the thing is zalloc'ed (like you said), it's already initialized. Probably we could just skip the INIT_HLIST_HEAD call altogether in the fscache_cookie_alloc, but David has a pile of patches in flight that rework this code substantially, so I wouldn't worry about it at the moment. -- Jeff Layton