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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 B0D13C2B9F4 for ; Tue, 22 Jun 2021 16:35:47 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 038C860FE7 for ; Tue, 22 Jun 2021 16:35:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 038C860FE7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; 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bh=cuRKHgNJV30vvy+CRuy5M/GcKM3GzTdsx3lkTsJf8Ks=; b=e9kGjT4tY9BkHC4nBmu8aj2NOfcjl9O7qreru+ppcGnbQmw52dJLRUiyBKndKfHBwl4saJ /o/VFW0N2A1uE2lnUOEtEr3cfQpjczx+vuaP4hkHPV+BtYrzyIkELUK5a8qOPv8bYA6LCA WKBhiwH8i92pVq0CU5U1v02k0c0KCxc= 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-151-Zsvntp59Nw6TOxkXbk20eA-1; Tue, 22 Jun 2021 12:34:43 -0400 X-MC-Unique: Zsvntp59Nw6TOxkXbk20eA-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 553C7CC622; Tue, 22 Jun 2021 16:34:42 +0000 (UTC) Received: from redhat.com (ovpn-114-58.ams2.redhat.com [10.36.114.58]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5B3DB60854; Tue, 22 Jun 2021 16:34:41 +0000 (UTC) Date: Tue, 22 Jun 2021 18:34:39 +0200 From: Kevin Wolf To: Max Reitz Subject: Re: [PATCH 3/4] export/fuse: Let permissions be adjustable Message-ID: References: <20210614144407.134243-1-mreitz@redhat.com> <20210614144407.134243-4-mreitz@redhat.com> <8f2a3abb-4b42-6257-51b9-08982cd87cb4@redhat.com> MIME-Version: 1.0 In-Reply-To: <8f2a3abb-4b42-6257-51b9-08982cd87cb4@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.223, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 22.06.2021 um 17:22 hat Max Reitz geschrieben: > On 22.06.21 17:02, Kevin Wolf wrote: > > Am 14.06.2021 um 16:44 hat Max Reitz geschrieben: > > > Allow changing the file mode, UID, and GID through SETATTR. > > > > > > This only really makes sense with allow-other, though (because without > > > it, the effective access mode is fixed to be 0600 (u+rw) with qemu's > > > user being the file's owner), so changing these stat fields is not > > > allowed without allow-other. > > > > > > Signed-off-by: Max Reitz > > > --- > > > block/export/fuse.c | 48 ++++++++++++++++++++++++++++++++++----------- > > > 1 file changed, 37 insertions(+), 11 deletions(-) > > > > > > diff --git a/block/export/fuse.c b/block/export/fuse.c > > > index 1d54286d90..742e0af657 100644 > > > --- a/block/export/fuse.c > > > +++ b/block/export/fuse.c > > > @@ -47,6 +47,10 @@ typedef struct FuseExport { > > > bool writable; > > > bool growable; > > > bool allow_other; > > > + > > > + mode_t st_mode; > > > + uid_t st_uid; > > > + gid_t st_gid; > > > } FuseExport; > > > static GHashTable *exports; > > > @@ -120,6 +124,13 @@ static int fuse_export_create(BlockExport *blk_exp, > > > exp->growable = args->growable; > > > exp->allow_other = args->allow_other; > > > + exp->st_mode = S_IFREG | S_IRUSR; > > > + if (exp->writable) { > > > + exp->st_mode |= S_IWUSR; > > > + } > > > + exp->st_uid = getuid(); > > > + exp->st_gid = getgid(); > > > + > > > ret = setup_fuse_export(exp, args->mountpoint, errp); > > > if (ret < 0) { > > > goto fail; > > > @@ -329,7 +340,6 @@ static void fuse_getattr(fuse_req_t req, fuse_ino_t inode, > > > int64_t length, allocated_blocks; > > > time_t now = time(NULL); > > > FuseExport *exp = fuse_req_userdata(req); > > > - mode_t mode; > > > length = blk_getlength(exp->common.blk); > > > if (length < 0) { > > > @@ -344,17 +354,12 @@ static void fuse_getattr(fuse_req_t req, fuse_ino_t inode, > > > allocated_blocks = DIV_ROUND_UP(allocated_blocks, 512); > > > } > > > - mode = S_IFREG | S_IRUSR; > > > - if (exp->writable) { > > > - mode |= S_IWUSR; > > > - } > > > - > > > statbuf = (struct stat) { > > > .st_ino = inode, > > > - .st_mode = mode, > > > + .st_mode = exp->st_mode, > > > .st_nlink = 1, > > > - .st_uid = getuid(), > > > - .st_gid = getgid(), > > > + .st_uid = exp->st_uid, > > > + .st_gid = exp->st_gid, > > > .st_size = length, > > > .st_blksize = blk_bs(exp->common.blk)->bl.request_alignment, > > > .st_blocks = allocated_blocks, > > > @@ -400,15 +405,23 @@ static int fuse_do_truncate(const FuseExport *exp, int64_t size, > > > } > > > /** > > > - * Let clients set file attributes. Only resizing is supported. > > > + * Let clients set file attributes. With allow_other, only resizing and > > > + * changing permissions (st_mode, st_uid, st_gid) is allowed. Without > > > + * allow_other, only resizing is supported. > > > */ > > > static void fuse_setattr(fuse_req_t req, fuse_ino_t inode, struct stat *statbuf, > > > int to_set, struct fuse_file_info *fi) > > > { > > > FuseExport *exp = fuse_req_userdata(req); > > > + int supported_attrs; > > > int ret; > > > - if (to_set & ~FUSE_SET_ATTR_SIZE) { > > > + supported_attrs = FUSE_SET_ATTR_SIZE; > > > + if (exp->allow_other) { > > > + supported_attrs |= FUSE_SET_ATTR_MODE | FUSE_SET_ATTR_UID | > > > + FUSE_SET_ATTR_GID; > > > + } > > > + if (to_set & ~supported_attrs) { > > > fuse_reply_err(req, ENOTSUP); > > > return; > > > } > > > @@ -426,6 +439,19 @@ static void fuse_setattr(fuse_req_t req, fuse_ino_t inode, struct stat *statbuf, > > > } > > > } > > > + if (to_set & FUSE_SET_ATTR_MODE) { > > > + /* Only allow changing the file mode, not the type */ > > > + exp->st_mode = (statbuf->st_mode & 07777) | S_IFREG; > > > + } > > Should we check that the mode actually makes sense? Not sure if making > > an image executable has a good use case, and making it writable in the > > permissions for a read-only export isn't a good idea either. > > I mean, I don’t mind what the user does.  It doesn’t really faze us, I > believe.  If the image contains an executable ELF and the user wants to run > it directly from FUSE...  I don’t mind. > > As for +w on RO exports, I’m not sure.  This reminds me of `sudo chattr +i > $file`, which effectively makes any regular file read-only, too, and it can > still keep +w.  So the file permissions are basically just ACLs, getting > permission for something doesn’t mean you can actually do it. > > OTOH, the difference to `chattr +i` is that we’d allow opening the export > R/W, only writing would then fail.  `chattr +i` does give EPERM when opening > the file. > > So I’m not quite sure.  I don’t really want to prevent the user from setting > any access restrictions they want, but on the other hand, if writing can > never work, then there really is no point in allowing +w.  (Then I’m > wondering, if we don’t allow +w, should we silently drop it or return an > error?  I guess returning success but not actually succeeding is weird, so > we probably should return EROFS.) Yes, EROFS seems best. > But +x can technically work, so I wouldn’t disallow it. Fair enough. Kevin