From patchwork Thu Aug 22 05:16:33 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 11108431 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 8E4FB184E for ; Thu, 22 Aug 2019 05:17:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C75B233A0 for ; Thu, 22 Aug 2019 05:17:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566451024; bh=yzhaukcaSnL+omUgwfIeGfqDRR+hnWkwJeBkb+A7NYk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=eQ2iMvZ6jOTRnhlQ/+SZx1sFyWLBydsTLMlX3o0AU14Xii7iuW30i9dbAxSkJMOcO jGmGwl+zt+Y6fGfZSGiQqL2wC5VHEk9xelyZmVlT044SOtma5S9E30EH4bhyQtA/rN 4RR0gvgjuzPxha4tBJYGNirBfMablMG9Ii0jj68I= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729069AbfHVFRD (ORCPT ); Thu, 22 Aug 2019 01:17:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:35718 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729050AbfHVFRD (ORCPT ); Thu, 22 Aug 2019 01:17:03 -0400 Received: from zzz.localdomain (unknown [67.218.105.90]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1F83B21848; Thu, 22 Aug 2019 05:17:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566451022; bh=yzhaukcaSnL+omUgwfIeGfqDRR+hnWkwJeBkb+A7NYk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aSKbDNVhKd27nMAHowOYVdU6WAz2q5R41mh4QzA0oPuEKuv/0cELUDt1irTEMU8H6 KOpUB4xMcZ4lv+IeurXOcF67FIBQSborUCE8ZB9Nb8dpUe2Kiqwmtf5clAGkAJ0Pmo ZhL3kZjwguJbeN6/mbJwgRGyQZ70PxjCGAzYQJQw= From: Eric Biggers To: Alexander Viro , linux-fsdevel@vger.kernel.org Cc: syzkaller-bugs@googlegroups.com, syzbot+7d6a57304857423318a5@syzkaller.appspotmail.com, David Howells , Miklos Szeredi Subject: [PATCH] vfs: set fs_context::user_ns for reconfigure Date: Wed, 21 Aug 2019 22:16:33 -0700 Message-Id: <20190822051633.12980-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.22.1 In-Reply-To: <0000000000007bc3a0058e460627@google.com> References: <0000000000007bc3a0058e460627@google.com> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Eric Biggers fs_context::user_ns is used by fuse_parse_param(), even during remount, so it needs to be set to the existing value for reconfigure. Reproducer: #include #include int main() { char opts[128]; int fd = open("/dev/fuse", O_RDWR); sprintf(opts, "fd=%d,rootmode=040000,user_id=0,group_id=0", fd); mkdir("mnt", 0777); mount("foo", "mnt", "fuse.foo", 0, opts); mount("foo", "mnt", "fuse.foo", MS_REMOUNT, opts); } Crash: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP CPU: 0 PID: 129 Comm: syz_make_kuid Not tainted 5.3.0-rc5-next-20190821 #3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014 RIP: 0010:map_id_range_down+0xb/0xc0 kernel/user_namespace.c:291 [...] Call Trace: map_id_down kernel/user_namespace.c:312 [inline] make_kuid+0xe/0x10 kernel/user_namespace.c:389 fuse_parse_param+0x116/0x210 fs/fuse/inode.c:523 vfs_parse_fs_param+0xdb/0x1b0 fs/fs_context.c:145 vfs_parse_fs_string+0x6a/0xa0 fs/fs_context.c:188 generic_parse_monolithic+0x85/0xc0 fs/fs_context.c:228 parse_monolithic_mount_data+0x1b/0x20 fs/fs_context.c:708 do_remount fs/namespace.c:2525 [inline] do_mount+0x39a/0xa60 fs/namespace.c:3107 ksys_mount+0x7d/0xd0 fs/namespace.c:3325 __do_sys_mount fs/namespace.c:3339 [inline] __se_sys_mount fs/namespace.c:3336 [inline] __x64_sys_mount+0x20/0x30 fs/namespace.c:3336 do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe Reported-by: syzbot+7d6a57304857423318a5@syzkaller.appspotmail.com Fixes: 408cbe695350 ("vfs: Convert fuse to use the new mount API") Cc: David Howells Cc: Miklos Szeredi Signed-off-by: Eric Biggers --- fs/fs_context.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/fs/fs_context.c b/fs/fs_context.c index cc61d305dc4b..44c4174b250a 100644 --- a/fs/fs_context.c +++ b/fs/fs_context.c @@ -279,10 +279,8 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type, fc->user_ns = get_user_ns(reference->d_sb->s_user_ns); break; case FS_CONTEXT_FOR_RECONFIGURE: - /* We don't pin any namespaces as the superblock's - * subscriptions cannot be changed at this point. - */ atomic_inc(&reference->d_sb->s_active); + fc->user_ns = get_user_ns(reference->d_sb->s_user_ns); fc->root = dget(reference); break; }