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[2.205.64.187]) by smtp.gmail.com with ESMTPSA id y8-20020aa7c248000000b005164ae1c482sm678387edo.11.2023.06.08.08.43.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Jun 2023 08:43:28 -0700 (PDT) From: Alexander Mikhalitsyn To: xiubli@redhat.com Cc: brauner@kernel.org, stgraber@ubuntu.com, linux-fsdevel@vger.kernel.org, Jeff Layton , Ilya Dryomov , ceph-devel@vger.kernel.org, Christian Brauner , Alexander Mikhalitsyn , linux-kernel@vger.kernel.org Subject: [PATCH v5 03/14] ceph: handle idmapped mounts in create_request_message() Date: Thu, 8 Jun 2023 17:42:44 +0200 Message-Id: <20230608154256.562906-4-aleksandr.mikhalitsyn@canonical.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230608154256.562906-1-aleksandr.mikhalitsyn@canonical.com> References: <20230608154256.562906-1-aleksandr.mikhalitsyn@canonical.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org From: Christian Brauner Inode operations that create a new filesystem object such as ->mknod, ->create, ->mkdir() and others don't take a {g,u}id argument explicitly. Instead the caller's fs{g,u}id is used for the {g,u}id of the new filesystem object. Cephfs mds creation request argument structures mirror this filesystem behavior. They don't encode a {g,u}id explicitly. Instead the caller's fs{g,u}id that is always sent as part of any mds request is used by the servers to set the {g,u}id of the new filesystem object. In order to ensure that the correct {g,u}id is used map the caller's fs{g,u}id for creation requests. This doesn't require complex changes. It suffices to pass in the relevant idmapping recorded in the request message. If this request message was triggered from an inode operation that creates filesystem objects it will have passed down the relevant idmaping. If this is a request message that was triggered from an inode operation that doens't need to take idmappings into account the initial idmapping is passed down which is an identity mapping and thus is guaranteed to leave the caller's fs{g,u}id unchanged.,u}id is sent. The last few weeks before Christmas 2021 I have spent time not just reading and poking the cephfs kernel code but also took a look at the ceph mds server userspace to ensure I didn't miss some subtlety. This made me aware of one complication to solve. All requests send the caller's fs{g,u}id over the wire. The caller's fs{g,u}id matters for the server in exactly two cases: 1. to set the ownership for creation requests 2. to determine whether this client is allowed access on this server Case 1. we already covered and explained. Case 2. is only relevant for servers where an explicit uid access restriction has been set. That is to say the mds server restricts access to requests coming from a specific uid. Servers without uid restrictions will grant access to requests from any uid by setting MDS_AUTH_UID_ANY. Case 2. introduces the complication because the caller's fs{g,u}id is not just used to record ownership but also serves as the {g,u}id used when checking access to the server. Consider a user mounting a cephfs client and creating an idmapped mount from it that maps files owned by uid 1000 to be owned uid 0: mount -t cephfs -o [...] /unmapped mount-idmapped --map-mount 1000:0:1 /idmapped That is to say if the mounted cephfs filesystem contains a file "file1" which is owned by uid 1000: - looking at it via /unmapped/file1 will report it as owned by uid 1000 (One can think of this as the on-disk value.) - looking at it via /idmapped/file1 will report it as owned by uid 0 Now, consider creating new files via the idmapped mount at /idmapped. When a caller with fs{g,u}id 1000 creates a file "file2" by going through the idmapped mount mounted at /idmapped it will create a file that is owned by uid 1000 on-disk, i.e.: - looking at it via /unmapped/file2 will report it as owned by uid 1000 - looking at it via /idmapped/file2 will report it as owned by uid 0 Now consider an mds server that has a uid access restriction set and only grants access to requests from uid 0. If the client sends a creation request for a file e.g. /idmapped/file2 it will send the caller's fs{g,u}id idmapped according to the idmapped mount. So if the caller has fs{g,u}id 1000 it will be mapped to {g,u}id 0 in the idmapped mount and will be sent over the wire allowing the caller access to the mds server. However, if the caller is not issuing a creation request the caller's fs{g,u}id will be send without the mount's idmapping applied. So if the caller that just successfully created a new file on the restricted mds server sends a request as fs{g,u}id 1000 access will be refused. This however is inconsistent. From my perspective the root of the problem lies in the fact that creation requests implicitly infer the ownership from the {g,u}id that gets sent along with every mds request. I have thought of multiple ways of addressing this problem but the one I prefer is to give all mds requests that create a filesystem object a proper, separate {g,u}id field entry in the argument struct. This is, for example how ->setattr mds requests work. This way the caller's fs{g,u}id can be used consistenly for server access checks and is separated from the ownership for new filesystem objects. Servers could then be updated to refuse creation requests whenever the {g,u}id used for access checking doesn't match the {g,u}id used for creating the filesystem object just as is done for setattr requests on a uid restricted server. But I am, of course, open to other suggestions. Cc: Xiubo Li Cc: Jeff Layton Cc: Ilya Dryomov Cc: ceph-devel@vger.kernel.org Signed-off-by: Christian Brauner Signed-off-by: Alexander Mikhalitsyn --- fs/ceph/mds_client.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index 05a99a8eb292..8826be3c209f 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -2581,6 +2581,8 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session, void *p, *end; int ret; bool legacy = !(session->s_con.peer_features & CEPH_FEATURE_FS_BTIME); + kuid_t caller_fsuid; + kgid_t caller_fsgid; ret = set_request_path_attr(req->r_inode, req->r_dentry, req->r_parent, req->r_path1, req->r_ino1.ino, @@ -2649,10 +2651,22 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session, head->mdsmap_epoch = cpu_to_le32(mdsc->mdsmap->m_epoch); head->op = cpu_to_le32(req->r_op); - head->caller_uid = cpu_to_le32(from_kuid(&init_user_ns, - req->r_cred->fsuid)); - head->caller_gid = cpu_to_le32(from_kgid(&init_user_ns, - req->r_cred->fsgid)); + /* + * Inode operations that create filesystem objects based on the + * caller's fs{g,u}id like ->mknod(), ->create(), ->mkdir() etc. don't + * have separate {g,u}id fields in their respective structs in the + * ceph_mds_request_args union. Instead the caller_{g,u}id field is + * used to set ownership of the newly created inode by the mds server. + * For these inode operations we need to send the mapped fs{g,u}id over + * the wire. For other cases we simple set req->r_mnt_idmap to the + * initial idmapping meaning the unmapped fs{g,u}id is sent. + */ + caller_fsuid = from_vfsuid(req->r_mnt_idmap, &init_user_ns, + VFSUIDT_INIT(req->r_cred->fsuid)); + caller_fsgid = from_vfsgid(req->r_mnt_idmap, &init_user_ns, + VFSGIDT_INIT(req->r_cred->fsgid)); + head->caller_uid = cpu_to_le32(from_kuid(&init_user_ns, caller_fsuid)); + head->caller_gid = cpu_to_le32(from_kgid(&init_user_ns, caller_fsgid)); head->ino = cpu_to_le64(req->r_deleg_ino); head->args = req->r_args;