fuse: support idmapped FUSE_EXT_GROUPS

We don't need to remap parent_gid, but have to adjust
group membership checks and take idmapping into account.
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dir.c

@@ -545,17 +545,21 @@ static u32 fuse_ext_size(size_t size)
 /*
  * This adds just a single supplementary group that matches the parent's group.
  */
-static int get_create_supp_group(struct inode *dir, struct fuse_in_arg *ext)
+static int get_create_supp_group(struct mnt_idmap *idmap,
+				 struct inode *dir,
+				 struct fuse_in_arg *ext)
 {
 	struct fuse_conn *fc = get_fuse_conn(dir);
 	struct fuse_ext_header *xh;
 	struct fuse_supp_groups *sg;
 	kgid_t kgid = dir->i_gid;
+	vfsgid_t vfsgid = make_vfsgid(idmap, fc->user_ns, kgid);
 	gid_t parent_gid = from_kgid(fc->user_ns, kgid);
+
 	u32 sg_len = fuse_ext_size(sizeof(*sg) + sizeof(sg->groups[0]));
 
-	if (parent_gid == (gid_t) -1 || gid_eq(kgid, current_fsgid()) ||
-	    !in_group_p(kgid))
+	if (parent_gid == (gid_t) -1 || vfsgid_eq_kgid(vfsgid, current_fsgid()) ||
+	    !vfsgid_in_group_p(vfsgid))
 		return 0;
 
 	xh = extend_arg(ext, sg_len);
@@ -572,7 +576,8 @@ 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_create_ext(struct mnt_idmap *idmap,
+			  struct fuse_args *args,
 			  struct inode *dir, struct dentry *dentry,
 			  umode_t mode)
 {
@@ -583,7 +588,7 @@ static int get_create_ext(struct fuse_args *args,
 	if (fc->init_security)
 		err = get_security_context(dentry, mode, &ext);
 	if (!err && fc->create_supp_group)
-		err = get_create_supp_group(dir, &ext);
+		err = get_create_supp_group(idmap, dir, &ext);
 
 	if (!err && ext.size) {
 		WARN_ON(args->in_numargs >= ARRAY_SIZE(args->in_args));
@@ -668,7 +673,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	args.out_args[1].size = sizeof(*outopenp);
 	args.out_args[1].value = outopenp;
 
-	err = get_create_ext(&args, dir, entry, mode);
+	err = get_create_ext(&nop_mnt_idmap, &args, dir, entry, mode);
 	if (err)
 		goto out_free_ff;
 
@@ -798,7 +803,7 @@ 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;
 	}