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 X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 169B8C433E6 for ; Fri, 5 Feb 2021 09:27:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B9F5064FBF for ; Fri, 5 Feb 2021 09:27:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230324AbhBEJ1F (ORCPT ); Fri, 5 Feb 2021 04:27:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44068 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230258AbhBEJYs (ORCPT ); Fri, 5 Feb 2021 04:24:48 -0500 Received: from mail-pg1-x52f.google.com (mail-pg1-x52f.google.com [IPv6:2607:f8b0:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C52F2C061793; Fri, 5 Feb 2021 01:24:07 -0800 (PST) Received: by mail-pg1-x52f.google.com with SMTP id n10so4110648pgl.10; Fri, 05 Feb 2021 01:24:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=q2XdoJkLIugwL6PyCTK0JiidlqGVW8dYDvt5+f3iTgo=; b=HbEpzL/prLHZw4lsA0c+8XxX5cS+ZWm4/dPyLpy8GWitl401Md5AGB2JzjYrcTEkwL 5pZ0HXj79jg2ghQPjH3IIp/GY3y2vzaiz7EnF6LZg3scLvN8K9qBb0sT/SxIFZ1vliFm jwa8tTekHufDnt7jBbdj3JI34ny6/e4bBJqYkCIs3mrl+ckS/ft7xFwc2bIpY8p8SMz0 ciIDbw1aNo0YPdOBJAwlyULFn4ZjwKNMZn7gCpf/aP0kIYlpUZFNJnbmZcwJqoSLR2Zn iFmk2oXY9KzU+4AMBi+UWpFunMMymDUM5zjay+NK2jy+DATH4crNVAk/dQCjeBmiuw/c SnHA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=q2XdoJkLIugwL6PyCTK0JiidlqGVW8dYDvt5+f3iTgo=; b=aAMPxB8tnc6+039fb1QIDw/l7aCrz7+D8NPOd7T9zNq5M47LyNVkEMrUCQGZ8tEse8 x0qE0iYp/8Zaw90KTok5lXAX5zRyvwjN2Uz6dvXLSJ6qS37DLdmdXNPfVOhZmInXhxwY 3L5TSxHL+k/+2+iDKzccT31cZ/wLH5Pxq7QWRyNacORXCulyc/cZ8qPixJP/AMnFY1mC YFnvfwnS9UpKjspqCF556DemEcPD45tQ1XBphm9qrfTg+syojdy3Qz2UAuTRRdArNZcl q+PLDY2y7U7fKV38Gp6oMf9PBiVDuoGC1acn0V2g0eu+v+zM1VdfJR42pzJ7sx06PNxh 15EQ== X-Gm-Message-State: AOAM532kVwz9ufCLxQk25dsTZ3oo4c43WUvIBGg+dxD9CKU9e6PXnbt4 SpefU1zVJj7B44xOK1PfiHtDX/72MukNFe4VTyg= X-Google-Smtp-Source: ABdhPJx0l70MIZqD5qtN1LAQxR401emhKr9GK5VLLauOP1OVKdj7bASNmX6cF8xvawt83I5j0x3CcDaNZjzFPPhqamM= X-Received: by 2002:a65:678b:: with SMTP id e11mr3480265pgr.140.1612517047283; Fri, 05 Feb 2021 01:24:07 -0800 (PST) MIME-Version: 1.0 References: <20210125153057.3623715-1-balsini@android.com> <20210125153057.3623715-8-balsini@android.com> In-Reply-To: <20210125153057.3623715-8-balsini@android.com> From: Peng Tao Date: Fri, 5 Feb 2021 17:23:56 +0800 Message-ID: Subject: Re: [PATCH RESEND V12 7/8] fuse: Use daemon creds in passthrough mode To: Alessio Balsini Cc: Miklos Szeredi , Akilesh Kailash , Amir Goldstein , Antonio SJ Musumeci , David Anderson , Giuseppe Scrivano , Jann Horn , Jens Axboe , Martijn Coenen , Palmer Dabbelt , Paul Lawrence , Stefano Duo , Zimuzo Ezeozue , wuyan , fuse-devel@lists.sourceforge.net, kernel-team@android.com, "linux-fsdevel@vger.kernel.org" , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Jan 25, 2021 at 11:31 PM Alessio Balsini wrote: > > When using FUSE passthrough, read/write operations are directly > forwarded to the lower file system file through VFS, but there is no > guarantee that the process that is triggering the request has the right > permissions to access the lower file system. This would cause the > read/write access to fail. > > In passthrough file systems, where the FUSE daemon is responsible for > the enforcement of the lower file system access policies, often happens > that the process dealing with the FUSE file system doesn't have access > to the lower file system. > Being the FUSE daemon in charge of implementing the FUSE file > operations, that in the case of read/write operations usually simply > results in the copy of memory buffers from/to the lower file system > respectively, these operations are executed with the FUSE daemon > privileges. > > This patch adds a reference to the FUSE daemon credentials, referenced > at FUSE_DEV_IOC_PASSTHROUGH_OPEN ioctl() time so that they can be used > to temporarily raise the user credentials when accessing lower file > system files in passthrough. > The process accessing the FUSE file with passthrough enabled temporarily > receives the privileges of the FUSE daemon while performing read/write > operations. Similar behavior is implemented in overlayfs. > These privileges will be reverted as soon as the IO operation completes. > This feature does not provide any higher security privileges to those > processes accessing the FUSE file system with passthrough enabled. This > is because it is still the FUSE daemon responsible for enabling or not > the passthrough feature at file open time, and should enable the feature > only after appropriate access policy checks. > > Signed-off-by: Alessio Balsini > --- > fs/fuse/fuse_i.h | 5 ++++- > fs/fuse/passthrough.c | 11 +++++++++++ > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index c4730d893324..815af1845b16 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -182,10 +182,13 @@ struct fuse_release_args; > > /** > * Reference to lower filesystem file for read/write operations handled in > - * passthrough mode > + * passthrough mode. > + * This struct also tracks the credentials to be used for handling read/write > + * operations. > */ > struct fuse_passthrough { > struct file *filp; > + struct cred *cred; > }; > > /** FUSE specific file data */ > diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c > index c7fa1eeb7639..24866c5fe7e2 100644 > --- a/fs/fuse/passthrough.c > +++ b/fs/fuse/passthrough.c > @@ -52,6 +52,7 @@ ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse, > struct iov_iter *iter) > { > ssize_t ret; > + const struct cred *old_cred; > struct file *fuse_filp = iocb_fuse->ki_filp; > struct fuse_file *ff = fuse_filp->private_data; > struct file *passthrough_filp = ff->passthrough.filp; > @@ -59,6 +60,7 @@ ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse, > if (!iov_iter_count(iter)) > return 0; > > + old_cred = override_creds(ff->passthrough.cred); > if (is_sync_kiocb(iocb_fuse)) { > ret = vfs_iter_read(passthrough_filp, iter, &iocb_fuse->ki_pos, > iocb_to_rw_flags(iocb_fuse->ki_flags, > @@ -77,6 +79,7 @@ ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse, > if (ret != -EIOCBQUEUED) > fuse_aio_cleanup_handler(aio_req); > } > + revert_creds(old_cred); cred should be reverted when kmalloc() fails above. Cheers, Tao -- Into Sth. Rich & Strange