From patchwork Fri Jun 4 16:11:50 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kurz X-Patchwork-Id: 12300055 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 707F7C4708F for ; Fri, 4 Jun 2021 16:12:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 51CEF61405 for ; Fri, 4 Jun 2021 16:12:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231357AbhFDQOG convert rfc822-to-8bit (ORCPT ); Fri, 4 Jun 2021 12:14:06 -0400 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:23005 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230453AbhFDQOF (ORCPT ); Fri, 4 Jun 2021 12:14:05 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-441-qyATIiLGPKW1OSiO_cFJ0g-1; Fri, 04 Jun 2021 12:12:13 -0400 X-MC-Unique: qyATIiLGPKW1OSiO_cFJ0g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C26C5802938; Fri, 4 Jun 2021 16:12:11 +0000 (UTC) Received: from bahia.lan (ovpn-112-232.ams2.redhat.com [10.36.112.232]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2F2F7687CE; Fri, 4 Jun 2021 16:12:09 +0000 (UTC) From: Greg Kurz To: Miklos Szeredi Cc: linux-kernel@vger.kernel.org, Max Reitz , linux-fsdevel@vger.kernel.org, virtio-fs@redhat.com, Vivek Goyal , Greg Kurz , stable@vger.kernel.org Subject: [PATCH v2 1/7] fuse: Fix crash in fuse_dentry_automount() error path Date: Fri, 4 Jun 2021 18:11:50 +0200 Message-Id: <20210604161156.408496-2-groug@kaod.org> In-Reply-To: <20210604161156.408496-1-groug@kaod.org> References: <20210604161156.408496-1-groug@kaod.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=groug@kaod.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kaod.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org If fuse_fill_super_submount() returns an error, the error path triggers a crash: [ 26.206673] BUG: kernel NULL pointer dereference, address: 0000000000000000 [...] [ 26.226362] RIP: 0010:__list_del_entry_valid+0x25/0x90 [...] [ 26.247938] Call Trace: [ 26.248300] fuse_mount_remove+0x2c/0x70 [fuse] [ 26.248892] virtio_kill_sb+0x22/0x160 [virtiofs] [ 26.249487] deactivate_locked_super+0x36/0xa0 [ 26.250077] fuse_dentry_automount+0x178/0x1a0 [fuse] The crash happens because fuse_mount_remove() assumes that the FUSE mount was already added to list under the FUSE connection, but this only done after fuse_fill_super_submount() has returned success. This means that until fuse_fill_super_submount() has returned success, the FUSE mount isn't actually owned by the superblock. We should thus reclaim ownership by clearing sb->s_fs_info, which will skip the call to fuse_mount_remove(), and perform rollback, like virtio_fs_get_tree() already does for the root sb. Fixes: bf109c64040f ("fuse: implement crossmounts") Cc: mreitz@redhat.com Cc: stable@vger.kernel.org # v5.10+ Signed-off-by: Greg Kurz Reviewed-by: Max Reitz --- fs/fuse/dir.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index 1b6c001a7dd1..01559061cbfb 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -339,8 +339,12 @@ static struct vfsmount *fuse_dentry_automount(struct path *path) /* Initialize superblock, making @mp_fi its root */ err = fuse_fill_super_submount(sb, mp_fi); - if (err) + if (err) { + fuse_conn_put(fc); + kfree(fm); + sb->s_fs_info = NULL; goto out_put_sb; + } sb->s_flags |= SB_ACTIVE; fsc->root = dget(sb->s_root);