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From:   Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
To:     xiubli@redhat.com
Cc:     brauner@kernel.org, stgraber@ubuntu.com,
        linux-fsdevel@vger.kernel.org, Jeff Layton <jlayton@kernel.org>,
        Ilya Dryomov <idryomov@gmail.com>, ceph-devel@vger.kernel.org,
        Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH v7 03/11] ceph: handle idmapped mounts in create_request_message()
Date:   Wed, 26 Jul 2023 16:10:18 +0200
Message-Id: <20230726141026.307690-4-aleksandr.mikhalitsyn@canonical.com>
In-Reply-To: <20230726141026.307690-1-aleksandr.mikhalitsyn@canonical.com>
References: <20230726141026.307690-1-aleksandr.mikhalitsyn@canonical.com>
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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.

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.

This change uses a new cephfs protocol extension CEPHFS_FEATURE_HAS_OWNER_UIDGID
which adds two new fields (owner_{u,g}id) to the request head structure.
So, we need to ensure that MDS supports it otherwise we need to fail
any IO that comes through an idmapped mount because we can't process it
in a proper way. MDS server without such an extension will use caller_{u,g}id
fields to set a new inode owner UID/GID which is incorrect because caller_{u,g}id
values are unmapped. At the same time we can't map these fields with an
idmapping as it can break UID/GID-based permission checks logic on the
MDS side. This problem was described with a lot of details at [1], [2].

[1] https://lore.kernel.org/lkml/CAEivzxfw1fHO2TFA4dx3u23ZKK6Q+EThfzuibrhA3RKM=ZOYLg@mail.gmail.com/
[2] https://lore.kernel.org/all/20220104140414.155198-3-brauner@kernel.org/

Cc: Xiubo Li <xiubli@redhat.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: ceph-devel@vger.kernel.org
Co-Developed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
---
v7:
	- reworked to use two new fields for owner UID/GID (https://github.com/ceph/ceph/pull/52575)
---
 fs/ceph/mds_client.c         | 20 ++++++++++++++++++++
 fs/ceph/mds_client.h         |  5 ++++-
 include/linux/ceph/ceph_fs.h |  4 +++-
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index c641ab046e98..ac095a95f3d0 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2923,6 +2923,7 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 {
 	int mds = session->s_mds;
 	struct ceph_mds_client *mdsc = session->s_mdsc;
+	struct ceph_client *cl = mdsc->fsc->client;
 	struct ceph_msg *msg;
 	struct ceph_mds_request_head_legacy *lhead;
 	const char *path1 = NULL;
@@ -3028,6 +3029,16 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 	lhead = find_legacy_request_head(msg->front.iov_base,
 					 session->s_con.peer_features);
 
+	if ((req->r_mnt_idmap != &nop_mnt_idmap) &&
+	    !test_bit(CEPHFS_FEATURE_HAS_OWNER_UIDGID, &session->s_features)) {
+		pr_err_ratelimited_client(cl,
+			"idmapped mount is used and CEPHFS_FEATURE_HAS_OWNER_UIDGID"
+			" is not supported by MDS. Fail request with -EIO.\n");
+
+		ret = -EIO;
+		goto out_err;
+	}
+
 	/*
 	 * The ceph_mds_request_head_legacy didn't contain a version field, and
 	 * one was added when we moved the message version from 3->4.
@@ -3043,10 +3054,19 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 		p = msg->front.iov_base + sizeof(*ohead);
 	} else {
 		struct ceph_mds_request_head *nhead = msg->front.iov_base;
+		kuid_t owner_fsuid;
+		kgid_t owner_fsgid;
 
 		msg->hdr.version = cpu_to_le16(6);
 		nhead->version = cpu_to_le16(CEPH_MDS_REQUEST_HEAD_VERSION);
 		p = msg->front.iov_base + sizeof(*nhead);
+
+		owner_fsuid = from_vfsuid(req->r_mnt_idmap, &init_user_ns,
+					  VFSUIDT_INIT(req->r_cred->fsuid));
+		owner_fsgid = from_vfsgid(req->r_mnt_idmap, &init_user_ns,
+					  VFSGIDT_INIT(req->r_cred->fsgid));
+		nhead->owner_uid = cpu_to_le32(from_kuid(&init_user_ns, owner_fsuid));
+		nhead->owner_gid = cpu_to_le32(from_kgid(&init_user_ns, owner_fsgid));
 	}
 
 	end = msg->front.iov_base + msg->front.iov_len;
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index e3bbf3ba8ee8..8f683e8203bd 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -33,8 +33,10 @@ enum ceph_feature_type {
 	CEPHFS_FEATURE_NOTIFY_SESSION_STATE,
 	CEPHFS_FEATURE_OP_GETVXATTR,
 	CEPHFS_FEATURE_32BITS_RETRY_FWD,
+	CEPHFS_FEATURE_NEW_SNAPREALM_INFO,
+	CEPHFS_FEATURE_HAS_OWNER_UIDGID,
 
-	CEPHFS_FEATURE_MAX = CEPHFS_FEATURE_32BITS_RETRY_FWD,
+	CEPHFS_FEATURE_MAX = CEPHFS_FEATURE_HAS_OWNER_UIDGID,
 };
 
 #define CEPHFS_FEATURES_CLIENT_SUPPORTED {	\
@@ -49,6 +51,7 @@ enum ceph_feature_type {
 	CEPHFS_FEATURE_NOTIFY_SESSION_STATE,	\
 	CEPHFS_FEATURE_OP_GETVXATTR,		\
 	CEPHFS_FEATURE_32BITS_RETRY_FWD,	\
+	CEPHFS_FEATURE_HAS_OWNER_UIDGID,	\
 }
 
 /*
diff --git a/include/linux/ceph/ceph_fs.h b/include/linux/ceph/ceph_fs.h
index 5f2301ee88bc..6eb83a51341c 100644
--- a/include/linux/ceph/ceph_fs.h
+++ b/include/linux/ceph/ceph_fs.h
@@ -499,7 +499,7 @@ struct ceph_mds_request_head_legacy {
 	union ceph_mds_request_args args;
 } __attribute__ ((packed));
 
-#define CEPH_MDS_REQUEST_HEAD_VERSION  2
+#define CEPH_MDS_REQUEST_HEAD_VERSION  3
 
 struct ceph_mds_request_head_old {
 	__le16 version;                /* struct version */
@@ -530,6 +530,8 @@ struct ceph_mds_request_head {
 
 	__le32 ext_num_retry;          /* new count retry attempts */
 	__le32 ext_num_fwd;            /* new count fwd attempts */
+
+	__le32 owner_uid, owner_gid;   /* used for OPs which create inodes */
 } __attribute__ ((packed));
 
 /* cap/lease release record */
-- 
2.34.1