security: define kernel_read_file hook

The kernel_read_file security hook is called prior to reading the file
into memory.

Changelog v4+:
- export security_kernel_read_file()
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Luis R. Rodriguez <mcgrof@kernel.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>

fs/exec.c

@@ -842,6 +842,10 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
 	if (!S_ISREG(file_inode(file)->i_mode) || max_size < 0)
 		return -EINVAL;
 
+	ret = security_kernel_read_file(file, id);
+	if (ret)
+		return ret;
+
 	i_size = i_size_read(file_inode(file));
 	if (max_size > 0 && i_size > max_size)
 		return -EFBIG;

include/linux/ima.h

@@ -19,6 +19,7 @@ extern int ima_file_check(struct file *file, int mask, int opened);
 extern void ima_file_free(struct file *file);
 extern int ima_file_mmap(struct file *file, unsigned long prot);
 extern int ima_module_check(struct file *file);
+extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
 
@@ -48,6 +49,11 @@ static inline int ima_module_check(struct file *file)
 	return 0;
 }
 
+static inline int ima_read_file(struct file *file, enum kernel_read_file_id id)
+{
+	return 0;
+}
+
 static inline int ima_post_read_file(struct file *file, void *buf, loff_t size,
 				     enum kernel_read_file_id id)
 {

include/linux/lsm_hooks.h

@@ -552,6 +552,12 @@
  *	the kernel module to load. If the module is being loaded from a blob,
  *	this argument will be NULL.
  *	Return 0 if permission is granted.
+ * @kernel_read_file:
+ *	Read a file specified by userspace.
+ *	@file contains the file structure pointing to the file being read
+ *	by the kernel.
+ *	@id kernel read file identifier
+ *	Return 0 if permission is granted.
  * @kernel_post_read_file:
  *	Read a file specified by userspace.
  *	@file contains the file structure pointing to the file being read
@@ -1455,6 +1461,7 @@ union security_list_options {
 	int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
 	int (*kernel_module_request)(char *kmod_name);
 	int (*kernel_module_from_file)(struct file *file);
+	int (*kernel_read_file)(struct file *file, enum kernel_read_file_id id);
 	int (*kernel_post_read_file)(struct file *file, char *buf, loff_t size,
 				     enum kernel_read_file_id id);
 	int (*task_fix_setuid)(struct cred *new, const struct cred *old,
@@ -1715,6 +1722,7 @@ struct security_hook_heads {
 	struct list_head cred_transfer;
 	struct list_head kernel_act_as;
 	struct list_head kernel_create_files_as;
+	struct list_head kernel_read_file;
 	struct list_head kernel_post_read_file;
 	struct list_head kernel_module_request;
 	struct list_head kernel_module_from_file;

include/linux/security.h

@@ -302,6 +302,7 @@ int security_kernel_act_as(struct cred *new, u32 secid);
 int security_kernel_create_files_as(struct cred *new, struct inode *inode);
 int security_kernel_module_request(char *kmod_name);
 int security_kernel_module_from_file(struct file *file);
+int security_kernel_read_file(struct file *file, enum kernel_read_file_id id);
 int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
 				   enum kernel_read_file_id id);
 int security_task_fix_setuid(struct cred *new, const struct cred *old,
@@ -863,6 +864,12 @@ static inline int security_kernel_module_from_file(struct file *file)
 	return 0;
 }
 
+static inline int security_kernel_read_file(struct file *file,
+					    enum kernel_read_file_id id)
+{
+	return 0;
+}
+
 static inline int security_kernel_post_read_file(struct file *file,
 						 char *buf, loff_t size,
 						 enum kernel_read_file_id id)

security/integrity/ima/ima_main.c

@@ -337,6 +337,22 @@ int ima_module_check(struct file *file)
 	return process_measurement(file, NULL, 0, MAY_EXEC, MODULE_CHECK, 0);
 }
 
+/**
+ * ima_read_file - pre-measure/appraise hook decision based on policy
+ * @file: pointer to the file to be measured/appraised/audit
+ * @read_id: caller identifier
+ *
+ * Permit reading a file based on policy. The policy rules are written
+ * in terms of the policy identifier.  Appraising the integrity of
+ * a file requires a file descriptor.
+ *
+ * For permission return 0, otherwise return -EACCES.
+ */
+int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
+{
+	return 0;
+}
+
 /**
  * ima_post_read_file - in memory collect/appraise/audit measurement
  * @file: pointer to the file to be measured/appraised/audit

security/security.c

@@ -899,6 +899,17 @@ int security_kernel_module_from_file(struct file *file)
 	return ima_module_check(file);
 }
 
+int security_kernel_read_file(struct file *file, enum kernel_read_file_id id)
+{
+	int ret;
+
+	ret = call_int_hook(kernel_read_file, 0, file, id);
+	if (ret)
+		return ret;
+	return ima_read_file(file, id);
+}
+EXPORT_SYMBOL_GPL(security_kernel_read_file);
+
 int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
 				   enum kernel_read_file_id id)
 {
@@ -1696,6 +1707,8 @@ struct security_hook_heads security_hook_heads = {
 		LIST_HEAD_INIT(security_hook_heads.kernel_module_request),
 	.kernel_module_from_file =
 		LIST_HEAD_INIT(security_hook_heads.kernel_module_from_file),
+	.kernel_read_file =
+		LIST_HEAD_INIT(security_hook_heads.kernel_read_file),
 	.kernel_post_read_file =
 		LIST_HEAD_INIT(security_hook_heads.kernel_post_read_file),
 	.task_fix_setuid =