Now we have everything in place and we can allow idmapped mounts by setting the FS_ALLOW_IDMAP flag. Notice that real availability of idmapped mounts will depend on the fuse daemon. Fuse daemon have to set FUSE_ALLOW_IDMAP flag in the FUSE_INIT reply. To discuss: - we enable idmapped mounts support only if "default_permissions" mode is enabled, because otherwise we would need to deal with UID/GID mappings in the userspace side OR provide the userspace with idmapped req->in.h.uid/req->in.h.gid values which is not something that we probably want to. Idmapped mounts phylosophy is not about faking caller uid/gid. - We have a small offlist discussion with Christian around adding fs_type->allow_idmap hook. Christian pointed that it would be nice to have a superblock flag instead like SB_I_NOIDMAP and we can set this flag during mount time if we see that filesystem does not support idmappings. But, unfortunately I didn't succeed here because the kernel will know if the filesystem supports idmapping or not after FUSE_INIT request, but FUSE_INIT request is being sent at the end of mounting process, so mount and superblock will exist and visible by the userspace in that time. It seems like setting SB_I_NOIDMAP flag in this case is too late as user may do the trick with creating a idmapped mount while it wasn't restricted by SB_I_NOIDMAP. Alternatively, we can introduce a "positive" version SB_I_ALLOWIDMAP and "weak" version of FS_ALLOW_IDMAP like FS_MAY_ALLOW_IDMAP. So if FS_MAY_ALLOW_IDMAP is set, then SB_I_ALLOWIDMAP has to be set on the superblock to allow creation of an idmapped mount. But that's a matter of our discussion. Some extra links and examples: - libfuse support https://github.com/mihalicyn/libfuse/commits/idmap_support - fuse-overlayfs support: https://github.com/mihalicyn/fuse-overlayfs/commits/idmap_support - cephfs-fuse conversion example https://github.com/mihalicyn/ceph/commits/fuse_idmap - glusterfs conversion example https://github.com/mihalicyn/glusterfs/commits/fuse_idmap Cc: Christian Brauner <brauner@xxxxxxxxxx> Cc: Seth Forshee <sforshee@xxxxxxxxxx> Cc: Miklos Szeredi <miklos@xxxxxxxxxx> Cc: Amir Goldstein <amir73il@xxxxxxxxx> Cc: Bernd Schubert <bschubert@xxxxxxx> Cc: <linux-fsdevel@xxxxxxxxxxxxxxx> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx> --- fs/fuse/fuse_i.h | 3 +++ fs/fuse/inode.c | 13 ++++++++++--- include/uapi/linux/fuse.h | 5 ++++- 3 files changed, 17 insertions(+), 4 deletions(-) diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index 883151a44d72..b2780ab59069 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -848,6 +848,9 @@ struct fuse_conn { /* Add owner_{u,g}id info when creating a new inode */ unsigned int owner_uid_gid_ext:1; + /* Allow creation of idmapped mounts */ + unsigned int allow_idmap:1; + /* Does the filesystem support per inode DAX? */ unsigned int inode_dax:1; diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index 6c205731c844..ed4c2688047f 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -1345,6 +1345,12 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args, fm->sb->s_export_op = &fuse_export_fid_operations; if (flags & FUSE_OWNER_UID_GID_EXT) fc->owner_uid_gid_ext = 1; + if (flags & FUSE_ALLOW_IDMAP) { + if (fc->owner_uid_gid_ext && fc->default_permissions) + fc->allow_idmap = 1; + else + ok = false; + } } else { ra_pages = fc->max_read / PAGE_SIZE; fc->no_lock = 1; @@ -1392,7 +1398,8 @@ void fuse_send_init(struct fuse_mount *fm) FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT | FUSE_INIT_EXT | FUSE_SECURITY_CTX | FUSE_CREATE_SUPP_GROUP | FUSE_HAS_EXPIRE_ONLY | FUSE_DIRECT_IO_ALLOW_MMAP | - FUSE_NO_EXPORT_SUPPORT | FUSE_HAS_RESEND | FUSE_OWNER_UID_GID_EXT; + FUSE_NO_EXPORT_SUPPORT | FUSE_HAS_RESEND | FUSE_OWNER_UID_GID_EXT | + FUSE_ALLOW_IDMAP; #ifdef CONFIG_FUSE_DAX if (fm->fc->dax) flags |= FUSE_MAP_ALIGNMENT; @@ -1981,7 +1988,7 @@ static void fuse_kill_sb_anon(struct super_block *sb) static struct file_system_type fuse_fs_type = { .owner = THIS_MODULE, .name = "fuse", - .fs_flags = FS_HAS_SUBTYPE | FS_USERNS_MOUNT, + .fs_flags = FS_HAS_SUBTYPE | FS_USERNS_MOUNT | FS_ALLOW_IDMAP, .init_fs_context = fuse_init_fs_context, .parameters = fuse_fs_parameters, .kill_sb = fuse_kill_sb_anon, @@ -2002,7 +2009,7 @@ static struct file_system_type fuseblk_fs_type = { .init_fs_context = fuse_init_fs_context, .parameters = fuse_fs_parameters, .kill_sb = fuse_kill_sb_blk, - .fs_flags = FS_REQUIRES_DEV | FS_HAS_SUBTYPE, + .fs_flags = FS_REQUIRES_DEV | FS_HAS_SUBTYPE | FS_ALLOW_IDMAP, }; MODULE_ALIAS_FS("fuseblk"); diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index d9ecc17fd13b..b23e8247ce43 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -221,6 +221,7 @@ * 7.41 * - add FUSE_EXT_OWNER_UID_GID * - add FUSE_OWNER_UID_GID_EXT + * - add FUSE_ALLOW_IDMAP */ #ifndef _LINUX_FUSE_H @@ -256,7 +257,7 @@ #define FUSE_KERNEL_VERSION 7 /** Minor version number of this interface */ -#define FUSE_KERNEL_MINOR_VERSION 40 +#define FUSE_KERNEL_MINOR_VERSION 41 /** The node ID of the root inode */ #define FUSE_ROOT_ID 1 @@ -427,6 +428,7 @@ struct fuse_file_lock { * of the request ID indicates resend requests * FUSE_OWNER_UID_GID_EXT: add inode owner UID/GID info to create, mkdir, * symlink and mknod + * FUSE_ALLOW_IDMAP: allow creation of idmapped mounts */ #define FUSE_ASYNC_READ (1 << 0) #define FUSE_POSIX_LOCKS (1 << 1) @@ -473,6 +475,7 @@ struct fuse_file_lock { /* Obsolete alias for FUSE_DIRECT_IO_ALLOW_MMAP */ #define FUSE_DIRECT_IO_RELAX FUSE_DIRECT_IO_ALLOW_MMAP #define FUSE_OWNER_UID_GID_EXT (1ULL << 40) +#define FUSE_ALLOW_IDMAP (1ULL << 41) /** * CUSE INIT request/reply flags -- 2.34.1
