From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3E50079FD for ; Mon, 4 Nov 2024 01:17:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730683073; cv=none; b=haHkZlnaLhwbg7WeXrJBVatgcw9cdJlQ5pjfRweX6te/rv6BZrzksm0UtWTjtRRiCgUKMlqJwmkkfMR/JXHUtVAz3qadzXycuQBMqBHMA5ZBvRtIsnNi5ikwlwiCb3M35O5/qO//a+TenbluvKgws5cx8rHesM8TON11Bx2szZM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730683073; c=relaxed/simple; bh=CHiz6ZQayHQ6uynSbdUX/cooiDXuv6Hc8hz/kwPQvVM=; h=Date:From:To:CC:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QQxFMB4swzvF66uESR0uncQUpeMa3jQQf+gS3AOmsM3hI+mtymX7FSkXNvxVS05gaowOgJs19hPwc0129TPrvKbjQA3ii6hPqzg9ky4xun+ymksemjzGHNbVgwOIYXrN4PN8kMTWv1PThx7Rj/es3Cbd2J12Rwi11RUQsPTg1bs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.194]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4XhYRY43vjzfdBH; Mon, 4 Nov 2024 09:15:05 +0800 (CST) Received: from dggpemf500017.china.huawei.com (unknown [7.185.36.126]) by mail.maildlp.com (Postfix) with ESMTPS id 55DA11402CB; Mon, 4 Nov 2024 09:17:41 +0800 (CST) Received: from localhost (10.175.127.227) by dggpemf500017.china.huawei.com (7.185.36.126) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 4 Nov 2024 09:17:41 +0800 Date: Mon, 4 Nov 2024 09:31:47 +0800 From: Long Li To: Chao Yu , CC: , , , , Subject: Re: [PATCH 1/2] f2fs: fix race in concurrent f2fs_stop_gc_thread Message-ID: <20241104013147.GA892643@ceph-admin> References: <20241031064553.55283-1-leo.lilong@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemf500017.china.huawei.com (7.185.36.126) On Fri, Nov 01, 2024 at 10:56:59AM +0800, Chao Yu wrote: > On 2024/10/31 14:45, Long Li wrote: > > In my test case, concurrent calls to f2fs shutdown report the following > > stack trace: > > > > Oops: general protection fault, probably for non-canonical address 0xc6cfff63bb5513fc: 0000 [#1] PREEMPT SMP PTI > > CPU: 0 UID: 0 PID: 678 Comm: f2fs_rep_shutdo Not tainted 6.12.0-rc5-next-20241029-g6fb2fa9805c5-dirty #85 > > Call Trace: > > > > ? show_regs+0x8b/0xa0 > > ? __die_body+0x26/0xa0 > > ? die_addr+0x54/0x90 > > ? exc_general_protection+0x24b/0x5c0 > > ? asm_exc_general_protection+0x26/0x30 > > ? kthread_stop+0x46/0x390 > > f2fs_stop_gc_thread+0x6c/0x110 > > f2fs_do_shutdown+0x309/0x3a0 > > f2fs_ioc_shutdown+0x150/0x1c0 > > __f2fs_ioctl+0xffd/0x2ac0 > > f2fs_ioctl+0x76/0xe0 > > vfs_ioctl+0x23/0x60 > > __x64_sys_ioctl+0xce/0xf0 > > x64_sys_call+0x2b1b/0x4540 > > do_syscall_64+0xa7/0x240 > > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > > > The root cause is a race condition in f2fs_stop_gc_thread() called from > > different f2fs shutdown paths: > > > > [CPU0] [CPU1] > > ---------------------- ----------------------- > > f2fs_stop_gc_thread f2fs_stop_gc_thread > > gc_th = sbi->gc_thread > > gc_th = sbi->gc_thread > > kfree(gc_th) > > sbi->gc_thread = NULL > > < gc_th != NULL > > > kthread_stop(gc_th->f2fs_gc_task) //UAF > > Hi Long, > > Thanks for catching this. > > Can we cover f2fs_stop_gc_thread() w/ write lock of s_umount in > f2fs_do_shutdown()? > > Thanks, > Hi Chao, If you think holding write lock inf2fs_do_shutdown() is better, I'll send v2 with this change. Thanks, Long Li > > > > The commit c7f114d864ac ("f2fs: fix to avoid use-after-free in > > f2fs_stop_gc_thread()") attempted to fix this issue by using a read > > semaphore to prevent races between shutdown and remount threads, but > > itfails to prevent all race conditions. > > > > While upgrading to s_umount write lock in f2fs_do_shutdown() would fix > > the current issue, however, using s_umount lock requires extreme caution > > to avoid lock recursion. A better solution is to introduce a semaphore > > to prevent races between concurrent f2fs_stop_gc_thread calls. > > > > Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown") > > Signed-off-by: Long Li > > --- > > fs/f2fs/f2fs.h | 1 + > > fs/f2fs/gc.c | 9 +++++++-- > > fs/f2fs/super.c | 1 + > > 3 files changed, 9 insertions(+), 2 deletions(-) > > > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h > > index 3c6f3cce5779..7ae1e2a4789f 100644 > > --- a/fs/f2fs/f2fs.h > > +++ b/fs/f2fs/f2fs.h > > @@ -1679,6 +1679,7 @@ struct f2fs_sb_info { > > * race between GC and GC or CP > > */ > > struct f2fs_gc_kthread *gc_thread; /* GC thread */ > > + struct semaphore gc_clean_lock; /* semaphore for clean GC thread */ > > struct atgc_management am; /* atgc management */ > > unsigned int cur_victim_sec; /* current victim section num */ > > unsigned int gc_mode; /* current GC state */ > > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c > > index e40bdd12e36d..e1b8bf98b5fa 100644 > > --- a/fs/f2fs/gc.c > > +++ b/fs/f2fs/gc.c > > @@ -232,14 +232,19 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi) > > void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi) > > { > > - struct f2fs_gc_kthread *gc_th = sbi->gc_thread; > > + struct f2fs_gc_kthread *gc_th; > > - if (!gc_th) > > + down(&sbi->gc_clean_lock); > > + gc_th = sbi->gc_thread; > > + if (!gc_th) { > > + up(&sbi->gc_clean_lock); > > return; > > + } > > kthread_stop(gc_th->f2fs_gc_task); > > wake_up_all(&gc_th->fggc_wq); > > kfree(gc_th); > > sbi->gc_thread = NULL; > > + up(&sbi->gc_clean_lock); > > } > > static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type) > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c > > index 80a53dbf1c38..47a15050ea9c 100644 > > --- a/fs/f2fs/super.c > > +++ b/fs/f2fs/super.c > > @@ -4419,6 +4419,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent) > > /* initialize locks within allocated memory */ > > init_f2fs_rwsem(&sbi->gc_lock); > > + sema_init(&sbi->gc_clean_lock, 1); > > mutex_init(&sbi->writepages); > > init_f2fs_rwsem(&sbi->cp_global_sem); > > init_f2fs_rwsem(&sbi->node_write); >