Re: [PATCH v9 03/12] ceph: handle idmapped mounts in create_request_message()

[Aleksandr Mikhalitsyn]

On Mon, Aug 7, 2023 at 3:25 AM Xiubo Li <xiubli@xxxxxxxxxx> wrote:
>
>
> On 8/4/23 16:48, Alexander Mikhalitsyn wrote:
> > From: Christian Brauner <brauner@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxx/
> > [2] https://lore.kernel.org/all/20220104140414.155198-3-brauner@xxxxxxxxxx/
> >
> > Link: https://github.com/ceph/ceph/pull/52575
> > Link: https://tracker.ceph.com/issues/62217
> > Cc: Xiubo Li <xiubli@xxxxxxxxxx>
> > Cc: Jeff Layton <jlayton@xxxxxxxxxx>
> > Cc: Ilya Dryomov <idryomov@xxxxxxxxx>
> > Cc: ceph-devel@xxxxxxxxxxxxxxx
> > Co-Developed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> > Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> > ---
> > v7:
> >       - reworked to use two new fields for owner UID/GID (https://github.com/ceph/ceph/pull/52575)
> > v8:
> >       - properly handled case when old MDS used with new kernel client
> > ---
> >   fs/ceph/mds_client.c         | 47 +++++++++++++++++++++++++++++++++---
> >   fs/ceph/mds_client.h         |  5 +++-
> >   include/linux/ceph/ceph_fs.h |  5 +++-
> >   3 files changed, 52 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> > index 8829f55103da..41e4bf3811c4 100644
> > --- a/fs/ceph/mds_client.c
> > +++ b/fs/ceph/mds_client.c
> > @@ -2902,6 +2902,17 @@ static void encode_mclientrequest_tail(void **p, const struct ceph_mds_request *
> >       }
> >   }
> >
> > +static inline u16 mds_supported_head_version(struct ceph_mds_session *session)
> > +{
> > +     if (!test_bit(CEPHFS_FEATURE_32BITS_RETRY_FWD, &session->s_features))
> > +             return 1;
> > +
> > +     if (!test_bit(CEPHFS_FEATURE_HAS_OWNER_UIDGID, &session->s_features))
> > +             return 2;
> > +
> > +     return CEPH_MDS_REQUEST_HEAD_VERSION;
> > +}
> > +
> >   static struct ceph_mds_request_head_legacy *
> >   find_legacy_request_head(void *p, u64 features)
> >   {
> > @@ -2923,6 +2934,7 @@ 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;
> > @@ -2936,7 +2948,7 @@ 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);
> > -     bool old_version = !test_bit(CEPHFS_FEATURE_32BITS_RETRY_FWD, &session->s_features);
> > +     u16 request_head_version = mds_supported_head_version(session);
> >
> >       ret = set_request_path_attr(mdsc, req->r_inode, req->r_dentry,
> >                             req->r_parent, req->r_path1, req->r_ino1.ino,
> > @@ -2977,8 +2989,10 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
> >        */
> >       if (legacy)
> >               len = sizeof(struct ceph_mds_request_head_legacy);
> > -     else if (old_version)
> > +     else if (request_head_version == 1)
> >               len = sizeof(struct ceph_mds_request_head_old);
> > +     else if (request_head_version == 2)
> > +             len = offsetofend(struct ceph_mds_request_head, ext_num_fwd);
> >       else
> >               len = sizeof(struct ceph_mds_request_head);
> >
> > @@ -3028,6 +3042,16 @@ 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.
> > @@ -3035,17 +3059,34 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
> >       if (legacy) {
> >               msg->hdr.version = cpu_to_le16(3);
> >               p = msg->front.iov_base + sizeof(*lhead);
> > -     } else if (old_version) {
> > +     } else if (request_head_version == 1) {
> >               struct ceph_mds_request_head_old *ohead = msg->front.iov_base;
> >
> >               msg->hdr.version = cpu_to_le16(4);
> >               ohead->version = cpu_to_le16(1);
> >               p = msg->front.iov_base + sizeof(*ohead);
> > +     } else if (request_head_version == 2) {
> > +             struct ceph_mds_request_head *nhead = msg->front.iov_base;
> > +
> > +             msg->hdr.version = cpu_to_le16(6);
> > +             nhead->version = cpu_to_le16(2);
> > +
> > +             p = msg->front.iov_base + offsetofend(struct ceph_mds_request_head, ext_num_fwd);
> >       } 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);
> > +             nhead->struct_len = sizeof(struct ceph_mds_request_head);
> > +
> > +             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));
> >               p = msg->front.iov_base + sizeof(*nhead);
> >       }
> >
> > 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..b91699b08f26 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 +530,9 @@ struct ceph_mds_request_head {
> >
> >       __le32 ext_num_retry;          /* new count retry attempts */
> >       __le32 ext_num_fwd;            /* new count fwd attempts */
> > +
> > +     __le32 struct_len;             /* to store size of struct ceph_mds_request_head */
> > +     __le32 owner_uid, owner_gid;   /* used for OPs which create inodes */
>
> Let's also initialize them to -1 for all the other requests as we do in
> your PR.

They are always initialized already. As you can see from the code we
don't have any extra conditions
on filling these fields. We always fill them with an appropriate
UID/GID. If mount is not idmapped then it's just == caller_uid/gid,
if mount idmapped then it's idmapped caller_uid/gid.

Kind regards,
Alex

>
> Thanks
>
> - Xiubo
>
>
>
> >   } __attribute__ ((packed));
> >
> >   /* cap/lease release record */
>