From nobody Sun Nov 24 17:03:30 2024 Received: from szxga07-in.huawei.com (szxga07-in.huawei.com [45.249.212.35]) (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 508555FDA7 for ; Mon, 4 Nov 2024 02:09:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.35 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730686168; cv=none; b=b7f40/BdI27dJJD7lnO0S/IxDEEqwiYZ3HMDDjmzyKjG8du6seOqZyKUtGg/GyTqeWI2hcZCqBCfRpT4FuPmUfeIHKFanc5OlkU5FJoyRVTqIgQjhDKp7xkVhwrQOUioyCRRl8p05pXeI4pDg4mpXOPyMIPkMQb0Lf2LHKEMaf8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730686168; c=relaxed/simple; bh=lVxzjs7sMv1wywKzBC5Zik+yLp5gMPmiFROLjLQUuko=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=Tl0PReuN3iiu2h0qh2KmIPWWyA32lltmJTf1vgGwOiXMU0sut/pW59d/nox6gsy3gZZ93UHhxZcuSkOkA3L9VT8T40NaA0WlDbI13XfUnbF4ezA7Nvd1lGlS7EAsE0Ux4TVUNfu8c0fbplUgEpXTSxRr9eCtYevn7jyYRnKX9JY= 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=45.249.212.35 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 [172.19.163.17]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4XhZc806H9z1SDqG; Mon, 4 Nov 2024 10:07:36 +0800 (CST) Received: from dggpemf500017.china.huawei.com (unknown [7.185.36.126]) by mail.maildlp.com (Postfix) with ESMTPS id A2A131A0188; Mon, 4 Nov 2024 10:09:14 +0800 (CST) Received: from huawei.com (10.175.104.67) 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 10:09:14 +0800 From: Long Li To: , CC: , , , , , Subject: [PATCH v2] f2fs: fix race in concurrent f2fs_stop_gc_thread Date: Mon, 4 Nov 2024 10:05:42 +0800 Message-ID: <20241104020542.2603607-1-leo.lilong@huawei.com> X-Mailer: git-send-email 2.39.2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemf500017.china.huawei.com (7.185.36.126) Content-Type: text/plain; charset="utf-8" In my test case, concurrent calls to f2fs shutdown report the following stack trace: Oops: general protection fault, probably for non-canonical address 0xc6cff= f63bb5513fc: 0000 [#1] PREEMPT SMP PTI CPU: 0 UID: 0 PID: 678 Comm: f2fs_rep_shutdo Not tainted 6.12.0-rc5-next-2= 0241029-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 =3D sbi->gc_thread gc_th =3D sbi->gc_thread kfree(gc_th) sbi->gc_thread =3D NULL < gc_th !=3D NULL > kthread_stop(gc_th->f2fs_gc_task) //UAF 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 it fails to prevent all race conditions. Fix it by converting to write lock of s_umount in f2fs_do_shutdown(). Fixes: 7950e9ac638e ("f2fs: stop gc/discard thread after fs shutdown") Signed-off-by: Long Li Reviewed-by: Chao Yu --- fs/f2fs/file.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index 75a8b22da664..703cfccc6b7e 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -2365,9 +2365,12 @@ int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsig= ned int flag, if (readonly) goto out; =20 - /* grab sb->s_umount to avoid racing w/ remount() */ + /* + * grab sb->s_umount to avoid racing w/ remount() and other shutdown + * paths. + */ if (need_lock) - down_read(&sbi->sb->s_umount); + down_write(&sbi->sb->s_umount); =20 f2fs_stop_gc_thread(sbi); f2fs_stop_discard_thread(sbi); @@ -2376,7 +2379,7 @@ int f2fs_do_shutdown(struct f2fs_sb_info *sbi, unsign= ed int flag, clear_opt(sbi, DISCARD); =20 if (need_lock) - up_read(&sbi->sb->s_umount); + up_write(&sbi->sb->s_umount); =20 f2fs_update_time(sbi, REQ_TIME); out: --=20 2.39.2