[PATCH v1 2/9] fs/fuse: add FUSE_OWNER_UID_GID_EXT extension

[Alexander Mikhalitsyn]

To properly support vfs idmappings we need to provide
a fuse daemon with the correct owner uid/gid for
inode creation requests like mkdir, mknod, atomic_open,
symlink.

Right now, fuse daemons use req->in.h.uid/req->in.h.gid
to set inode owner. These fields contain fsuid/fsgid of the
syscall's caller. And that's perfectly fine, because inode
owner have to be set to these values. But, for idmapped mounts
it's not the case and caller fsuid/fsgid != inode owner, because
idmapped mounts do nothing with the caller fsuid/fsgid, but
affect inode owner uid/gid. It means that we can't apply vfsid
mapping to caller fsuid/fsgid, but instead we have to introduce
a new fields to store inode owner uid/gid which will be appropriately
transformed.

Christian and I have done the same to support idmapped mounts in
the cephfs recently [1].

[1] 5ccd8530 ("ceph: handle idmapped mounts in create_request_message()")

Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Seth Forshee <sforshee@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/dir.c             | 34 +++++++++++++++++++++++++++++++---
 fs/fuse/fuse_i.h          |  3 +++
 fs/fuse/inode.c           |  4 +++-
 include/uapi/linux/fuse.h | 19 +++++++++++++++++++
 4 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 6f5f9ff95380..e78ad4742aef 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -568,7 +568,33 @@ static int get_create_supp_group(struct inode *dir, struct fuse_in_arg *ext)
 	return 0;
 }
 
-static int get_create_ext(struct fuse_args *args,
+static int get_owner_uid_gid(struct mnt_idmap *idmap, struct fuse_conn *fc, struct fuse_in_arg *ext)
+{
+	struct fuse_ext_header *xh;
+	struct fuse_owner_uid_gid *owner_creds;
+	u32 owner_creds_len = fuse_ext_size(sizeof(*owner_creds));
+	kuid_t owner_fsuid;
+	kgid_t owner_fsgid;
+
+	xh = extend_arg(ext, owner_creds_len);
+	if (!xh)
+		return -ENOMEM;
+
+	xh->size = owner_creds_len;
+	xh->type = FUSE_EXT_OWNER_UID_GID;
+
+	owner_creds = (struct fuse_owner_uid_gid *) &xh[1];
+
+	owner_fsuid = mapped_fsuid(idmap, fc->user_ns);
+	owner_fsgid = mapped_fsgid(idmap, fc->user_ns);
+	owner_creds->uid = from_kuid(fc->user_ns, owner_fsuid);
+	owner_creds->gid = from_kgid(fc->user_ns, owner_fsgid);
+
+	return 0;
+}
+
+static int get_create_ext(struct mnt_idmap *idmap,
+			  struct fuse_args *args,
 			  struct inode *dir, struct dentry *dentry,
 			  umode_t mode)
 {
@@ -580,6 +606,8 @@ static int get_create_ext(struct fuse_args *args,
 		err = get_security_context(dentry, mode, &ext);
 	if (!err && fc->create_supp_group)
 		err = get_create_supp_group(dir, &ext);
+	if (!err && fc->owner_uid_gid_ext)
+		err = get_owner_uid_gid(idmap, fc, &ext);
 
 	if (!err && ext.size) {
 		WARN_ON(args->in_numargs >= ARRAY_SIZE(args->in_args));
@@ -662,7 +690,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	args.out_args[1].size = sizeof(outopen);
 	args.out_args[1].value = &outopen;
 
-	err = get_create_ext(&args, dir, entry, mode);
+	err = get_create_ext(&nop_mnt_idmap, &args, dir, entry, mode);
 	if (err)
 		goto out_put_forget_req;
 
@@ -790,7 +818,7 @@ static int create_new_entry(struct fuse_mount *fm, struct fuse_args *args,
 	args->out_args[0].value = &outarg;
 
 	if (args->opcode != FUSE_LINK) {
-		err = get_create_ext(args, dir, entry, mode);
+		err = get_create_ext(&nop_mnt_idmap, args, dir, entry, mode);
 		if (err)
 			goto out_put_forget_req;
 	}
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 1df83eebda92..15ec95dea276 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -806,6 +806,9 @@ struct fuse_conn {
 	/* Add supplementary group info when creating a new inode */
 	unsigned int create_supp_group:1;
 
+	/* Add owner_{u,g}id info when creating a new inode */
+	unsigned int owner_uid_gid_ext: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 ab824a8908b7..08cd3714b32d 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1284,6 +1284,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
 				fc->create_supp_group = 1;
 			if (flags & FUSE_DIRECT_IO_ALLOW_MMAP)
 				fc->direct_io_allow_mmap = 1;
+			if (flags & FUSE_OWNER_UID_GID_EXT)
+				fc->owner_uid_gid_ext = 1;
 		} else {
 			ra_pages = fc->max_read / PAGE_SIZE;
 			fc->no_lock = 1;
@@ -1330,7 +1332,7 @@ void fuse_send_init(struct fuse_mount *fm)
 		FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA |
 		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_HAS_EXPIRE_ONLY | FUSE_DIRECT_IO_ALLOW_MMAP | FUSE_OWNER_UID_GID_EXT;
 #ifdef CONFIG_FUSE_DAX
 	if (fm->fc->dax)
 		flags |= FUSE_MAP_ALIGNMENT;
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index e7418d15fe39..ebe82104b172 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -211,6 +211,10 @@
  *  7.39
  *  - add FUSE_DIRECT_IO_ALLOW_MMAP
  *  - add FUSE_STATX and related structures
+ *
+ *  7.40
+ *  - add FUSE_EXT_OWNER_UID_GID
+ *  - add FUSE_OWNER_UID_GID_EXT
  */
 
 #ifndef _LINUX_FUSE_H
@@ -410,6 +414,8 @@ struct fuse_file_lock {
  *			symlink and mknod (single group that matches parent)
  * FUSE_HAS_EXPIRE_ONLY: kernel supports expiry-only entry invalidation
  * FUSE_DIRECT_IO_ALLOW_MMAP: allow shared mmap in FOPEN_DIRECT_IO mode.
+ * FUSE_OWNER_UID_GID_EXT: add inode owner UID/GID info to create, mkdir,
+ *			   symlink and mknod
  */
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
@@ -452,6 +458,7 @@ 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 << 37)
 
 /**
  * CUSE INIT request/reply flags
@@ -561,11 +568,13 @@ struct fuse_file_lock {
  * extension type
  * FUSE_MAX_NR_SECCTX: maximum value of &fuse_secctx_header.nr_secctx
  * FUSE_EXT_GROUPS: &fuse_supp_groups extension
+ * FUSE_EXT_OWNER_UID_GID: &fuse_owner_uid_gid extension
  */
 enum fuse_ext_type {
 	/* Types 0..31 are reserved for fuse_secctx_header */
 	FUSE_MAX_NR_SECCTX	= 31,
 	FUSE_EXT_GROUPS		= 32,
+	FUSE_EXT_OWNER_UID_GID	= 33,
 };
 
 enum fuse_opcode {
@@ -1153,4 +1162,14 @@ struct fuse_supp_groups {
 	uint32_t	groups[];
 };
 
+/**
+ * struct fuse_owner_uid_gid - Inode owner UID/GID extension
+ * @uid: inode owner UID
+ * @gid: inode owner GID
+ */
+struct fuse_owner_uid_gid {
+	uint32_t	uid;
+	uint32_t	gid;
+};
+
 #endif /* _LINUX_FUSE_H */
-- 
2.34.1