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 48F1CC433EF for ; Sat, 26 Mar 2022 03:16:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230123AbiCZDS2 (ORCPT ); Fri, 25 Mar 2022 23:18:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37558 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229893AbiCZDS0 (ORCPT ); Fri, 25 Mar 2022 23:18:26 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 94065139871 for ; Fri, 25 Mar 2022 20:16:50 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 410CDB82B03 for ; Sat, 26 Mar 2022 03:16:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD24EC004DD; Sat, 26 Mar 2022 03:16:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1648264608; bh=dHJWpreyfBpL+3sjTnmiaJlC5+wD5lu1Qm+7kzu6LXo=; h=Date:To:From:Subject:From; b=q5k5QsDuG+7Z2cek9yGAh92M1kMnFUjOFBf6fHpMfEGXDiGWbYgri+7G+FyAilfC1 a0BRNsB9bHmpuZ6UIG5bXXK6Plo8cLRl/YzDakxhOHloRwFYn+OVa0zTsn+n0BrGYE 2Mpq6Iw9Qp8PUopAb6atBgfebgognCNZxg+uzICo= Date: Fri, 25 Mar 2022 20:16:47 -0700 To: mm-commits@vger.kernel.org, viro@zeniv.linux.org.uk, sridhar.samudrala@intel.com, soheil@google.com, kuni1840@gmail.com, dave@stgolabs.net, alexander.h.duyck@intel.com, akpm@linux-foundation.org, kuniyu@amazon.co.jp, akpm@linux-foundation.org From: Andrew Morton Subject: + list-fix-a-data-race-around-ep-rdllist.patch added to -mm tree Message-Id: <20220326031647.DD24EC004DD@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: list: fix a data-race around ep->rdllist has been added to the -mm tree. Its filename is list-fix-a-data-race-around-ep-rdllist.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/list-fix-a-data-race-around-ep-rdllist.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/list-fix-a-data-race-around-ep-rdllist.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Kuniyuki Iwashima Subject: list: fix a data-race around ep->rdllist ep_poll() first calls ep_events_available() with no lock held and checks if ep->rdllist is empty by list_empty_careful(), which reads rdllist->prev. Thus all accesses to it need some protection to avoid store/load-tearing. Note INIT_LIST_HEAD_RCU() already has the annotation for both prev and next. Commit bf3b9f6372c4 ("epoll: Add busy poll support to epoll with socket fds.") added the first lockless ep_events_available(), and commit c5a282e9635e ("fs/epoll: reduce the scope of wq lock in epoll_wait()") made some ep_events_available() calls lockless and added single call under a lock, finally commit e59d3c64cba6 ("epoll: eliminate unnecessary lock for zero timeout") made the last ep_events_available() lockless. BUG: KCSAN: data-race in do_epoll_wait / do_epoll_wait write to 0xffff88810480c7d8 of 8 bytes by task 1802 on cpu 0: INIT_LIST_HEAD include/linux/list.h:38 [inline] list_splice_init include/linux/list.h:492 [inline] ep_start_scan fs/eventpoll.c:622 [inline] ep_send_events fs/eventpoll.c:1656 [inline] ep_poll fs/eventpoll.c:1806 [inline] do_epoll_wait+0x4eb/0xf40 fs/eventpoll.c:2234 do_epoll_pwait fs/eventpoll.c:2268 [inline] __do_sys_epoll_pwait fs/eventpoll.c:2281 [inline] __se_sys_epoll_pwait+0x12b/0x240 fs/eventpoll.c:2275 __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2275 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae read to 0xffff88810480c7d8 of 8 bytes by task 1799 on cpu 1: list_empty_careful include/linux/list.h:329 [inline] ep_events_available fs/eventpoll.c:381 [inline] ep_poll fs/eventpoll.c:1797 [inline] do_epoll_wait+0x279/0xf40 fs/eventpoll.c:2234 do_epoll_pwait fs/eventpoll.c:2268 [inline] __do_sys_epoll_pwait fs/eventpoll.c:2281 [inline] __se_sys_epoll_pwait+0x12b/0x240 fs/eventpoll.c:2275 __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2275 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae value changed: 0xffff88810480c7d0 -> 0xffff888103c15098 Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 1799 Comm: syz-fuzzer Tainted: G W 5.17.0-rc7-syzkaller-dirty #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Link: https://lkml.kernel.org/r/20220322002653.33865-3-kuniyu@amazon.co.jp Fixes: e59d3c64cba6 ("epoll: eliminate unnecessary lock for zero timeout") Fixes: c5a282e9635e ("fs/epoll: reduce the scope of wq lock in epoll_wait()") Fixes: bf3b9f6372c4 ("epoll: Add busy poll support to epoll with socket fds.") Signed-off-by: Kuniyuki Iwashima Reported-by: syzbot+bdd6e38a1ed5ee58d8bd@syzkaller.appspotmail.com Cc: Al Viro , Andrew Morton Cc: Kuniyuki Iwashima Cc: Kuniyuki Iwashima Cc: "Soheil Hassas Yeganeh" Cc: Davidlohr Bueso Cc: "Sridhar Samudrala" Cc: Alexander Duyck Signed-off-by: Andrew Morton --- include/linux/list.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/include/linux/list.h~list-fix-a-data-race-around-ep-rdllist +++ a/include/linux/list.h @@ -35,7 +35,7 @@ static inline void INIT_LIST_HEAD(struct list_head *list) { WRITE_ONCE(list->next, list); - list->prev = list; + WRITE_ONCE(list->prev, list); } #ifdef CONFIG_DEBUG_LIST @@ -306,7 +306,7 @@ static inline int list_empty(const struc static inline void list_del_init_careful(struct list_head *entry) { __list_del_entry(entry); - entry->prev = entry; + WRITE_ONCE(entry->prev, entry); smp_store_release(&entry->next, entry); } @@ -326,7 +326,7 @@ static inline void list_del_init_careful static inline int list_empty_careful(const struct list_head *head) { struct list_head *next = smp_load_acquire(&head->next); - return list_is_head(next, head) && (next == head->prev); + return list_is_head(next, head) && (next == READ_ONCE(head->prev)); } /** _ Patches currently in -mm which might be from kuniyu@amazon.co.jp are pipe-make-poll_usage-boolean-and-annotate-its-access.patch list-fix-a-data-race-around-ep-rdllist.patch