[PATCH v2 2/6] configfd: add generic file descriptor based configuration parser

[James Bottomley <James.Bottomley@HansenPartnership.com>]

This code is based on the original filesystem context based
configuration parser by David Howells, but lifted up so it can apply
to anything rather than only filesystem contexts.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 fs/Makefile                   |   3 +-
 fs/configfd.c                 | 450 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/configfd.h      |  61 ++++++
 include/uapi/linux/configfd.h |  20 ++
 4 files changed, 533 insertions(+), 1 deletion(-)
 create mode 100644 fs/configfd.c
 create mode 100644 include/linux/configfd.h
 create mode 100644 include/uapi/linux/configfd.h

diff --git a/fs/Makefile b/fs/Makefile
index 1148c555c4d3..de83671ce80d 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -13,7 +13,8 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o splice.o sync.o utimes.o d_path.o \
 		stack.o fs_struct.o statfs.o fs_pin.o nsfs.o \
-		fs_types.o fs_context.o fs_parser.o fsopen.o
+		fs_types.o fs_context.o fs_parser.o fsopen.o \
+		configfd.o
 
 ifeq ($(CONFIG_BLOCK),y)
 obj-y +=	buffer.o block_dev.o direct-io.o mpage.o
diff --git a/fs/configfd.c b/fs/configfd.c
new file mode 100644
index 000000000000..7f2c750ac7e3
--- /dev/null
+++ b/fs/configfd.c
@@ -0,0 +1,450 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Generic configuration file descriptor handling
+ *
+ * Copyright (C) 2019 James.Bottomley@HansenPartnership.com
+ */
+
+#include <linux/anon_inodes.h>
+#include <linux/configfd.h>
+#include <linux/namei.h>
+#include <linux/slab.h>
+#include <linux/syscalls.h>
+#include <linux/rwlock.h>
+#include <linux/uaccess.h>
+
+
+static struct configfd_type *configfds;
+static DEFINE_RWLOCK(configfds_lock);
+
+static ssize_t configfd_read(struct file *file,
+			     char __user *buf, size_t len, loff_t *pos)
+{
+	struct configfd_context *cfc = file->private_data;
+
+	return logger_read(cfc->log, buf, len);
+}
+
+static void configfd_type_put(const struct configfd_type *cft)
+{
+	module_put(cft->owner);
+}
+
+static void configfd_context_free(struct configfd_context *cfc)
+{
+	if (cfc->cft->ops->free)
+		cfc->cft->ops->free(cfc);
+	logger_put(&cfc->log);
+	configfd_type_put(cfc->cft);
+	kfree(cfc);
+}
+
+static int configfd_release(struct inode *inode, struct file *file)
+{
+	struct configfd_context *cfc = file->private_data;
+
+	if (cfc) {
+		file->private_data = NULL;
+		configfd_context_free(cfc);
+	}
+	return 0;
+}
+
+const struct file_operations configfd_context_fops = {
+	.read		= configfd_read,
+	.release	= configfd_release,
+	.llseek		= no_llseek,
+};
+
+static int configfd_create_fd(struct configfd_context *cfc,
+			      unsigned int flags)
+{
+	int fd;
+
+	fd = anon_inode_getfd("[configfd]", &configfd_context_fops, cfc,
+			      O_RDWR | flags);
+	if (fd < 0)
+		configfd_context_free(cfc);
+	return fd;
+}
+
+static struct configfd_type **configfd_type_find(const char *name)
+{
+	struct configfd_type **c;
+
+	for (c = &configfds; *c; c = &(*c)->next) {
+		if (strcmp((*c)->name, name) == 0)
+			break;
+	}
+
+	return c;
+}
+
+static struct configfd_type *configfd_type_get(const char *name)
+{
+	struct configfd_type *cft;
+
+	read_lock(&configfds_lock);
+	cft = *(configfd_type_find(name));
+	if (cft && !try_module_get(cft->owner))
+		cft = NULL;
+	read_unlock(&configfds_lock);
+
+	return cft;
+}
+
+struct configfd_context *configfd_context_alloc(const struct configfd_type *cft,
+						unsigned int op)
+{
+	struct configfd_context *cfc;
+	struct logger *log;
+	int ret;
+
+	cfc = kzalloc(sizeof(*cfc) + cft->data_size, GFP_KERNEL);
+	if (!cfc)
+		return ERR_PTR(-ENOMEM);
+
+	if (cft->data_size)
+		cfc->data = &cfc[1];
+
+	cfc->cft = cft;
+	cfc->op = op;
+	log = logger_alloc(cft->owner);
+	if (IS_ERR(log)) {
+		ret = PTR_ERR(log);
+		goto out_free;
+	}
+
+	cfc->log = log;
+	if (cft->ops->alloc) {
+		ret = cft->ops->alloc(cfc);
+		if (ret)
+			goto out_put;
+	}
+
+	return cfc;
+ out_put:
+	logger_put(&cfc->log);
+ out_free:
+	kfree(cfc);
+	return ERR_PTR(ret);
+}
+
+int kern_configfd_open(const char *config_name, unsigned int flags,
+			unsigned int op)
+{
+	const struct configfd_type *cft;
+	struct configfd_context *cfc;
+
+	if (flags & ~O_CLOEXEC)
+		return -EINVAL;
+	if (op != CONFIGFD_CMD_CREATE && op != CONFIGFD_CMD_RECONFIGURE)
+		return -EINVAL;
+
+	cft = configfd_type_get(config_name);
+	if (!cft)
+		return -ENODEV;
+	cfc = configfd_context_alloc(cft, op);
+	if (IS_ERR(cfc)) {
+		configfd_type_put(cft);
+		return PTR_ERR(cfc);
+	}
+
+	return configfd_create_fd(cfc, flags);
+}
+
+long ksys_configfd_open(const char __user *_config_name, unsigned int flags,
+			unsigned int op)
+{
+	const char *config_name = strndup_user(_config_name, PAGE_SIZE);
+	int ret;
+
+	if (IS_ERR(config_name))
+		return PTR_ERR(config_name);
+	ret = kern_configfd_open(config_name, flags, op);
+	kfree(config_name);
+
+	return ret;
+}
+
+SYSCALL_DEFINE3(configfd_open,
+		const char __user *, _config_name,
+		unsigned int, flags,
+		unsigned int, op)
+{
+	return ksys_configfd_open(_config_name, flags, op);
+}
+
+int kern_configfd_action(int fd, struct configfd_param *p)
+{
+	struct fd f = fdget(fd);
+	struct configfd_context *cfc;
+	const struct configfd_ops *ops;
+	int ret = -EINVAL;
+	/* upper 24 bits are available to consumers */
+	u8 our_cmd = p->cmd & 0xff;
+
+	if (!f.file)
+		return -EBADF;
+	if (f.file->f_op != &configfd_context_fops)
+		goto out_f;
+	cfc = f.file->private_data;
+
+	ops = cfc->cft->ops;
+
+	/* check allowability */
+	ret = -EOPNOTSUPP;
+	switch (our_cmd) {
+	case CONFIGFD_SET_FLAG:
+	case CONFIGFD_SET_STRING:
+	case CONFIGFD_SET_BINARY:
+	case CONFIGFD_SET_PATH:
+	case CONFIGFD_SET_PATH_EMPTY:
+	case CONFIGFD_SET_INT:
+		if (!ops->set)
+			goto out_f;
+		break;
+	case CONFIGFD_GET_FD:
+		if (!ops->get)
+			goto out_f;
+		break;
+	case CONFIGFD_CMD_CREATE:
+	case CONFIGFD_CMD_RECONFIGURE:
+		if (our_cmd != cfc->op) {
+			logger_err(cfc->log, "Wrong operation, we were opened for %d", cfc->op);
+			goto out_f;
+		}
+		if (!ops->act)
+			goto out_f;
+		break;
+	default:
+		break;
+	}
+
+	/*
+	 * Execute
+	 */
+	switch (our_cmd) {
+	case CONFIGFD_SET_STRING:
+	case CONFIGFD_SET_BINARY:
+	case CONFIGFD_SET_PATH:
+	case CONFIGFD_SET_PATH_EMPTY:
+	case CONFIGFD_SET_FD:
+	case CONFIGFD_SET_FLAG:
+	case CONFIGFD_SET_INT:
+		ret = ops->set(cfc, p);
+		break;
+	case CONFIGFD_GET_FD:
+		ret = ops->get(cfc, p);
+		if (ret == 0) {
+			int fd;
+
+			fd = get_unused_fd_flags(p->aux & O_CLOEXEC);
+			if (fd < 0) {
+				ret = fd;
+				break;
+			}
+			fd_install(fd, p->file);
+			p->file = NULL; /* consume the file */
+			p->aux = fd;
+		}
+		break;
+	case CONFIGFD_CMD_RECONFIGURE:
+	case CONFIGFD_CMD_CREATE:
+		ret = ops->act(cfc, p->cmd);
+		break;
+	default:
+		break;
+	}
+out_f:
+	fdput(f);
+	return ret;
+}
+
+long ksys_configfd_action(int fd, unsigned int cmd, const char __user *_key,
+			  void __user *_value, int aux)
+{
+	struct configfd_param param = {
+		.cmd = cmd,
+	};
+	u8 our_cmd = cmd & 0xff;
+	int ret;
+
+	/* check parameters required for action */
+	switch (our_cmd) {
+	case CONFIGFD_SET_FLAG:
+		if (!_key || _value || aux)
+			return -EINVAL;
+		break;
+	case CONFIGFD_SET_STRING:
+	case CONFIGFD_GET_FD:
+		if (!_key || !_value)
+			return -EINVAL;
+		break;
+	case CONFIGFD_SET_BINARY:
+		if (!_key || !_value || aux <= 0 || aux > 1024 * 1024)
+			return -EINVAL;
+		break;
+	case CONFIGFD_SET_PATH:
+	case CONFIGFD_SET_PATH_EMPTY:
+		if (!_key || !_value || (aux != AT_FDCWD && aux < 0))
+			return -EINVAL;
+		break;
+	case CONFIGFD_SET_FD:
+		if (!_key || _value || aux < 0)
+			return -EINVAL;
+		break;
+	case CONFIGFD_SET_INT:
+		if (!_key)
+			return -EINVAL;
+		break;
+	case CONFIGFD_CMD_CREATE:
+	case CONFIGFD_CMD_RECONFIGURE:
+		if (_key || _value || aux)
+			return -EINVAL;
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	if (_key) {
+		param.key = strndup_user(_key, 256);
+		if (IS_ERR(param.key))
+			return PTR_ERR(param.key);
+	}
+
+	/* now pull the parameters into the kernel */
+	switch (our_cmd) {
+	case CONFIGFD_SET_STRING:
+		param.string = strndup_user(_value, 256);
+		if (IS_ERR(param.string)) {
+			ret = PTR_ERR(param.string);
+			goto out_key;
+		}
+		param.size = strlen(param.string);
+		break;
+	case CONFIGFD_SET_BINARY:
+		param.size = aux;
+		param.blob = memdup_user_nul(_value, aux);
+		if (IS_ERR(param.blob)) {
+			ret = PTR_ERR(param.blob);
+			goto out_key;
+		}
+		break;
+	case CONFIGFD_SET_PATH:
+		param.name = getname_flags(_value, 0, NULL);
+		if (IS_ERR(param.name)) {
+			ret = PTR_ERR(param.name);
+			goto out_key;
+		}
+		param.aux = aux;
+		param.size = strlen(param.name->name);
+		break;
+	case CONFIGFD_SET_PATH_EMPTY:
+		param.name = getname_flags(_value, LOOKUP_EMPTY, NULL);
+		if (IS_ERR(param.name)) {
+			ret = PTR_ERR(param.name);
+			goto out_key;
+		}
+		param.aux = aux;
+		param.size = strlen(param.name->name);
+		break;
+	case CONFIGFD_SET_FD:
+		ret = -EBADF;
+		param.file = fget_raw(aux);
+		if (!param.file)
+			goto out_key;
+		break;
+	case CONFIGFD_SET_INT:
+		param.aux = aux;
+		break;
+	default:
+		break;
+	}
+	ret = kern_configfd_action(fd, &param);
+	/* clean up unconsumed parameters */
+	switch (our_cmd) {
+	case CONFIGFD_SET_STRING:
+	case CONFIGFD_SET_BINARY:
+		kfree(param.string);
+		break;
+	case CONFIGFD_SET_PATH:
+	case CONFIGFD_SET_PATH_EMPTY:
+		if (param.name)
+			putname(param.name);
+		break;
+	case CONFIGFD_GET_FD:
+		if (!ret)
+			ret = put_user(param.aux, (int __user *)_value);
+		/* FALL THROUGH */
+	case CONFIGFD_SET_FD:
+		if (param.file)
+			fput(param.file);
+		break;
+	default:
+		break;
+	}
+ out_key:
+	kfree(param.key);
+
+	return ret;
+}
+
+
+SYSCALL_DEFINE5(configfd_action,
+		int, fd, unsigned int, cmd,
+		const char __user *, _key,
+		void __user *, _value,
+		int, aux)
+{
+	return ksys_configfd_action(fd, cmd, _key, _value, aux);
+}
+
+int configfd_type_register(struct configfd_type *cft)
+{
+	int ret = 0;
+	struct configfd_type **c;
+
+	if (WARN(cft->next,
+		 "BUG: registering already registered configfd_type: %s",
+		 cft->name))
+		return -EBUSY;
+
+	if (WARN(cft->ops == NULL,
+		 "BUG: configfd_type has no ops set: %s", cft->name))
+		return -EINVAL;
+
+	if (WARN(cft->ops->alloc && (!cft->ops->free),
+		 "BUG: if configfd ops alloc is set, free must also be"))
+		return -EINVAL;
+
+	if (WARN(cft->name == NULL || cft->name[0] == '\0',
+		 "BUG: configfd_type has no name"))
+		return -EINVAL;
+
+	write_lock(&configfds_lock);
+	c = configfd_type_find(cft->name);
+	if (WARN(*c, "BUG: configfd_type name already exists: %s",
+		 cft->name))
+		ret = -EBUSY;
+	else
+		*c = cft;
+	write_unlock(&configfds_lock);
+
+	return ret;
+}
+
+void configfd_type_unregister(struct configfd_type *cft)
+{
+	struct configfd_type **c;
+
+	write_lock(&configfds_lock);
+	c = configfd_type_find(cft->name);
+	if (WARN(*c != cft, "BUG: trying to register %s from wrong structure",
+		 cft->name))
+		goto out;
+	*c = cft->next;
+	cft->next = NULL;
+ out:
+	write_unlock(&configfds_lock);
+}
diff --git a/include/linux/configfd.h b/include/linux/configfd.h
new file mode 100644
index 000000000000..2a2efd7eabe2
--- /dev/null
+++ b/include/linux/configfd.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _LINUX_CONFIGFD_H
+#define _LINUX_CONFIGFD_H
+
+#include <linux/logger.h>
+
+#include <uapi/linux/configfd.h>
+
+struct configfd_context;
+
+struct configfd_param {
+	const char			*key;
+	union {
+		char			*string;
+		void			*blob;
+		struct filename		*name;
+		struct file		*file;
+	};
+	int				aux;
+	unsigned int			cmd;
+	size_t				size;
+};
+
+struct configfd_ops {
+	int (*alloc)(struct configfd_context *cfc);
+	void (*free)(const struct configfd_context *cfc);
+	int (*set)(const struct configfd_context *cfc,
+		   struct configfd_param *p);
+	int (*get)(const struct configfd_context *cfc,
+		   struct configfd_param *p);
+	int (*act)(const struct configfd_context *cfc, unsigned int cmd);
+};
+
+struct configfd_type {
+	const char		*name;
+	size_t			data_size;
+	struct module		*owner;
+	struct configfd_ops	*ops;
+	struct configfd_type	*next;
+};
+
+struct configfd_context {
+	const struct configfd_type	*cft;
+	struct logger			*log;
+	void				*data;
+	unsigned int			op;
+};
+
+int configfd_type_register(struct configfd_type *cft);
+void configfd_type_unregister(struct configfd_type *cft);
+
+long ksys_configfd_open(const char __user *config_name, unsigned int flags,
+			unsigned int op);
+long ksys_configfd_action(int fd, unsigned int cmd, const char __user *key,
+			  void __user *value, int aux);
+int kern_configfd_action(int fd, struct configfd_param *p);
+int kern_configfd_open(const char *name, unsigned int flags,
+		       unsigned int op);
+
+#endif
diff --git a/include/uapi/linux/configfd.h b/include/uapi/linux/configfd.h
new file mode 100644
index 000000000000..3e54cfef0182
--- /dev/null
+++ b/include/uapi/linux/configfd.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later WITH Linux-syscall-note */
+
+#ifndef _UAPI_LINUX_CONFIGFD_H
+#define _UAPI_LINUX_CONFIGFD_H
+
+enum configfd_cmd {
+	CONFIGFD_SET_FLAG		= 0,
+	CONFIGFD_SET_STRING		= 1,
+	CONFIGFD_SET_BINARY		= 2,
+	CONFIGFD_SET_PATH		= 3,
+	CONFIGFD_SET_PATH_EMPTY		= 4,
+	CONFIGFD_SET_FD			= 5,
+	CONFIGFD_CMD_CREATE		= 6,
+	CONFIGFD_CMD_RECONFIGURE	= 7,
+	/* gap for 30 other commands */
+	CONFIGFD_SET_INT		= 38,
+	CONFIGFD_GET_FD			= 39,
+};
+
+#endif
-- 
2.16.4