fuse: add request extension

Will need to add supplementary groups to create messages, so add the
general concept of a request extension.  A request extension is appended to
the end of the main request.  It has a header indicating the size and type
of the extension.

The create security context (fuse_secctx_*) is similar to the generic
request extension, so include that as well in a backward compatible manner.

Add the total extension length to the request header.  The offset of the
extension block within the request can be calculated by:

  inh->len - inh->total_extlen * 8

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dev.c

@@ -476,6 +476,8 @@ static void fuse_args_to_req(struct fuse_req *req, struct fuse_args *args)
 	req->in.h.opcode = args->opcode;
 	req->in.h.nodeid = args->nodeid;
 	req->args = args;
+	if (args->is_ext)
+		req->in.h.total_extlen = args->in_args[args->ext_idx].size / 8;
 	if (args->end)
 		__set_bit(FR_ASYNC, &req->flags);
 }

fs/fuse/dir.c

@@ -466,7 +466,7 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
 }
 
 static int get_security_context(struct dentry *entry, umode_t mode,
-				void **security_ctx, u32 *security_ctxlen)
+				struct fuse_in_arg *ext)
 {
 	struct fuse_secctx *fctx;
 	struct fuse_secctx_header *header;
@@ -513,14 +513,42 @@ static int get_security_context(struct dentry *entry, umode_t mode,
 
 		memcpy(ptr, ctx, ctxlen);
 	}
-	*security_ctxlen = total_len;
-	*security_ctx = header;
+	ext->size = total_len;
+	ext->value = header;
 	err = 0;
 out_err:
 	kfree(ctx);
 	return err;
 }
 
+static int get_create_ext(struct fuse_args *args, struct dentry *dentry,
+			  umode_t mode)
+{
+	struct fuse_conn *fc = get_fuse_conn_super(dentry->d_sb);
+	struct fuse_in_arg ext = { .size = 0, .value = NULL };
+	int err = 0;
+
+	if (fc->init_security)
+		err = get_security_context(dentry, mode, &ext);
+
+	if (!err && ext.size) {
+		WARN_ON(args->in_numargs >= ARRAY_SIZE(args->in_args));
+		args->is_ext = true;
+		args->ext_idx = args->in_numargs++;
+		args->in_args[args->ext_idx] = ext;
+	} else {
+		kfree(ext.value);
+	}
+
+	return err;
+}
+
+static void free_ext_value(struct fuse_args *args)
+{
+	if (args->is_ext)
+		kfree(args->in_args[args->ext_idx].value);
+}
+
 /*
  * Atomic create+open operation
  *
@@ -541,8 +569,6 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	struct fuse_entry_out outentry;
 	struct fuse_inode *fi;
 	struct fuse_file *ff;
-	void *security_ctx = NULL;
-	u32 security_ctxlen;
 	bool trunc = flags & O_TRUNC;
 
 	/* Userspace expects S_IFREG in create mode */
@@ -586,19 +612,12 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	args.out_args[1].size = sizeof(outopen);
 	args.out_args[1].value = &outopen;
 
-	if (fm->fc->init_security) {
-		err = get_security_context(entry, mode, &security_ctx,
-					   &security_ctxlen);
-		if (err)
-			goto out_put_forget_req;
-
-		args.in_numargs = 3;
-		args.in_args[2].size = security_ctxlen;
-		args.in_args[2].value = security_ctx;
-	}
+	err = get_create_ext(&args, entry, mode);
+	if (err)
+		goto out_put_forget_req;
 
 	err = fuse_simple_request(fm, &args);
-	kfree(security_ctx);
+	free_ext_value(&args);
 	if (err)
 		goto out_free_ff;
 
@@ -705,8 +724,6 @@ static int create_new_entry(struct fuse_mount *fm, struct fuse_args *args,
 	struct dentry *d;
 	int err;
 	struct fuse_forget_link *forget;
-	void *security_ctx = NULL;
-	u32 security_ctxlen;
 
 	if (fuse_is_bad(dir))
 		return -EIO;
@@ -721,21 +738,14 @@ static int create_new_entry(struct fuse_mount *fm, struct fuse_args *args,
 	args->out_args[0].size = sizeof(outarg);
 	args->out_args[0].value = &outarg;
 
-	if (fm->fc->init_security && args->opcode != FUSE_LINK) {
-		err = get_security_context(entry, mode, &security_ctx,
-					   &security_ctxlen);
+	if (args->opcode != FUSE_LINK) {
+		err = get_create_ext(args, entry, mode);
 		if (err)
 			goto out_put_forget_req;
-
-		BUG_ON(args->in_numargs != 2);
-
-		args->in_numargs = 3;
-		args->in_args[2].size = security_ctxlen;
-		args->in_args[2].value = security_ctx;
 	}
 
 	err = fuse_simple_request(fm, args);
-	kfree(security_ctx);
+	free_ext_value(args);
 	if (err)
 		goto out_put_forget_req;
 

fs/fuse/fuse_i.h

@@ -249,8 +249,9 @@ struct fuse_page_desc {
 struct fuse_args {
 	uint64_t nodeid;
 	uint32_t opcode;
-	unsigned short in_numargs;
-	unsigned short out_numargs;
+	uint8_t in_numargs;
+	uint8_t out_numargs;
+	uint8_t ext_idx;
 	bool force:1;
 	bool noreply:1;
 	bool nocreds:1;
@@ -261,6 +262,7 @@ struct fuse_args {
 	bool page_zeroing:1;
 	bool page_replace:1;
 	bool may_block:1;
+	bool is_ext:1;
 	struct fuse_in_arg in_args[3];
 	struct fuse_arg out_args[2];
 	void (*end)(struct fuse_mount *fm, struct fuse_args *args, int error);

include/uapi/linux/fuse.h

@@ -201,6 +201,9 @@
  *  7.38
  *  - add FUSE_EXPIRE_ONLY flag to fuse_notify_inval_entry
  *  - add FOPEN_PARALLEL_DIRECT_WRITES
+ *  - add total_extlen to fuse_in_header
+ *  - add FUSE_MAX_NR_SECCTX
+ *  - add extension header
  */
 
 #ifndef _LINUX_FUSE_H
@@ -503,6 +506,15 @@ struct fuse_file_lock {
  */
 #define FUSE_EXPIRE_ONLY		(1 << 0)
 
+/**
+ * extension type
+ * FUSE_MAX_NR_SECCTX: maximum value of &fuse_secctx_header.nr_secctx
+ */
+enum fuse_ext_type {
+	/* Types 0..31 are reserved for fuse_secctx_header */
+	FUSE_MAX_NR_SECCTX	= 31,
+};
+
 enum fuse_opcode {
 	FUSE_LOOKUP		= 1,
 	FUSE_FORGET		= 2,  /* no reply */
@@ -886,7 +898,8 @@ struct fuse_in_header {
 	uint32_t	uid;
 	uint32_t	gid;
 	uint32_t	pid;
-	uint32_t	padding;
+	uint16_t	total_extlen; /* length of extensions in 8byte units */
+	uint16_t	padding;
 };
 
 struct fuse_out_header {
@@ -1047,4 +1060,17 @@ struct fuse_secctx_header {
 	uint32_t	nr_secctx;
 };
 
+/**
+ * struct fuse_ext_header - extension header
+ * @size: total size of this extension including this header
+ * @type: type of extension
+ *
+ * This is made compatible with fuse_secctx_header by using type values >
+ * FUSE_MAX_NR_SECCTX
+ */
+struct fuse_ext_header {
+	uint32_t	size;
+	uint32_t	type;
+};
+
 #endif /* _LINUX_FUSE_H */