ima: Define new template fields xattrnames, xattrlengths and xattrvalues

This patch defines the new template fields xattrnames, xattrlengths and
xattrvalues, which contain respectively a list of xattr names (strings,
separated by |), lengths (u32, hex) and values (hex). If an xattr is not
present, the name and length are not displayed in the measurement list.

Reported-by: kernel test robot <[e-mail]> (Missing prototype def)
Signed-off-by: Roberto Sassu <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>

Documentation/security/IMA-templates.rst

···
  - 'iuid': the inode UID;
  - 'igid': the inode GID;
  - 'imode': the inode mode;
+ - 'xattrnames': a list of xattr names (separated by |), only if the xattr is
+    present;
+ - 'xattrlengths': a list of xattr lengths (u32), only if the xattr is present;
+ - 'xattrvalues': a list of xattr values;
 
 
 Below, there is the list of defined template descriptors:

include/linux/evm.h

···
 				   struct xattr *evm);
 extern bool evm_revalidate_status(const char *xattr_name);
 extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
+extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
+				     int buffer_size, char type,
+				     bool canonical_fmt);
 #ifdef CONFIG_FS_POSIX_ACL
 extern int posix_xattr_acl(const char *xattrname);
 #else
···
 static inline int evm_protected_xattr_if_enabled(const char *req_xattr_name)
 {
 	return false;
+}
+
+static inline int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
+					    int buffer_size, char type,
+					    bool canonical_fmt)
+{
+	return -EOPNOTSUPP;
 }
 
 #endif /* CONFIG_EVM */

security/integrity/evm/evm_main.c

···
 }
 
 /**
+ * evm_read_protected_xattrs - read EVM protected xattr names, lengths, values
+ * @dentry: dentry of the read xattrs
+ * @inode: inode of the read xattrs
+ * @buffer: buffer xattr names, lengths or values are copied to
+ * @buffer_size: size of buffer
+ * @type: n: names, l: lengths, v: values
+ * @canonical_fmt: data format (true: little endian, false: native format)
+ *
+ * Read protected xattr names (separated by |), lengths (u32) or values for a
+ * given dentry and return the total size of copied data. If buffer is NULL,
+ * just return the total size.
+ *
+ * Returns the total size on success, a negative value on error.
+ */
+int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
+			      int buffer_size, char type, bool canonical_fmt)
+{
+	struct xattr_list *xattr;
+	int rc, size, total_size = 0;
+
+	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
+		rc = __vfs_getxattr(dentry, d_backing_inode(dentry),
+				    xattr->name, NULL, 0);
+		if (rc < 0 && rc == -ENODATA)
+			continue;
+		else if (rc < 0)
+			return rc;
+
+		switch (type) {
+		case 'n':
+			size = strlen(xattr->name) + 1;
+			if (buffer) {
+				if (total_size)
+					*(buffer + total_size - 1) = '|';
+
+				memcpy(buffer + total_size, xattr->name, size);
+			}
+			break;
+		case 'l':
+			size = sizeof(u32);
+			if (buffer) {
+				if (canonical_fmt)
+					rc = cpu_to_le32(rc);
+
+				*(u32 *)(buffer + total_size) = rc;
+			}
+			break;
+		case 'v':
+			size = rc;
+			if (buffer) {
+				rc = __vfs_getxattr(dentry,
+					d_backing_inode(dentry), xattr->name,
+					buffer + total_size,
+					buffer_size - total_size);
+				if (rc < 0)
+					return rc;
+			}
+			break;
+		default:
+			return -EINVAL;
+		}
+
+		total_size += size;
+	}
+
+	return total_size;
+}
+
+/**
  * evm_verifyxattr - verify the integrity of the requested xattr
  * @dentry: object of the verify xattr
  * @xattr_name: requested xattr

security/integrity/ima/ima_template.c

···
 	 .field_show = ima_show_template_uint},
 	{.field_id = "imode", .field_init = ima_eventinodemode_init,
 	 .field_show = ima_show_template_uint},
+	{.field_id = "xattrnames",
+	 .field_init = ima_eventinodexattrnames_init,
+	 .field_show = ima_show_template_string},
+	{.field_id = "xattrlengths",
+	 .field_init = ima_eventinodexattrlengths_init,
+	 .field_show = ima_show_template_sig},
+	{.field_id = "xattrvalues",
+	 .field_init = ima_eventinodexattrvalues_init,
+	 .field_show = ima_show_template_sig},
 };
 
 /*

security/integrity/ima/ima_template_lib.c

···
 
 #include "ima_template_lib.h"
 #include <linux/xattr.h>
+#include <linux/evm.h>
 
 static bool ima_template_hash_algo_allowed(u8 algo)
 {
···
 
 	return ima_write_template_field_data((char *)&mode, sizeof(mode),
 					     DATA_FMT_UINT, field_data);
+}
+
+static int ima_eventinodexattrs_init_common(struct ima_event_data *event_data,
+					    struct ima_field_data *field_data,
+					    char type)
+{
+	u8 *buffer = NULL;
+	int rc;
+
+	if (!event_data->file)
+		return 0;
+
+	rc = evm_read_protected_xattrs(file_dentry(event_data->file), NULL, 0,
+				       type, ima_canonical_fmt);
+	if (rc < 0)
+		return 0;
+
+	buffer = kmalloc(rc, GFP_KERNEL);
+	if (!buffer)
+		return 0;
+
+	rc = evm_read_protected_xattrs(file_dentry(event_data->file), buffer,
+				       rc, type, ima_canonical_fmt);
+	if (rc < 0) {
+		rc = 0;
+		goto out;
+	}
+
+	rc = ima_write_template_field_data((char *)buffer, rc, DATA_FMT_HEX,
+					   field_data);
+out:
+	kfree(buffer);
+	return rc;
+}
+
+/*
+ *  ima_eventinodexattrnames_init - include a list of xattr names as part of the
+ *  template data
+ */
+int ima_eventinodexattrnames_init(struct ima_event_data *event_data,
+				  struct ima_field_data *field_data)
+{
+	return ima_eventinodexattrs_init_common(event_data, field_data, 'n');
+}
+
+/*
+ *  ima_eventinodexattrlengths_init - include a list of xattr lengths as part of
+ *  the template data
+ */
+int ima_eventinodexattrlengths_init(struct ima_event_data *event_data,
+				    struct ima_field_data *field_data)
+{
+	return ima_eventinodexattrs_init_common(event_data, field_data, 'l');
+}
+
+/*
+ *  ima_eventinodexattrvalues_init - include a list of xattr values as part of
+ *  the template data
+ */
+int ima_eventinodexattrvalues_init(struct ima_event_data *event_data,
+				   struct ima_field_data *field_data)
+{
+	return ima_eventinodexattrs_init_common(event_data, field_data, 'v');
 }

security/integrity/ima/ima_template_lib.h

···
 			   struct ima_field_data *field_data);
 int ima_eventinodemode_init(struct ima_event_data *event_data,
 			    struct ima_field_data *field_data);
+int ima_eventinodexattrnames_init(struct ima_event_data *event_data,
+				  struct ima_field_data *field_data);
+int ima_eventinodexattrlengths_init(struct ima_event_data *event_data,
+				    struct ima_field_data *field_data);
+int ima_eventinodexattrvalues_init(struct ima_event_data *event_data,
+				   struct ima_field_data *field_data);
 #endif /* __LINUX_IMA_TEMPLATE_LIB_H */