[PATCH v3 07/13] diglim: Interfaces - digest_list_add, digest_list_del

[Roberto Sassu]

Introduce <securityfs>/integrity/diglim/digest_list_add, which can be used
to upload a digest list and add the digests to the hash table; passed data
are interpreted as file path if the first byte is / or as the digest list
itself otherwise.

diglim_ima_get_info() is called to retrieve from IMA the digest of the
passed digest list (file or buffer), and the actions performed (measure/
appraise/appraise with signature).

Also introduce <securityfs>/integrity/diglim/digest_list_del, which can be
used to upload a digest list and delete the digests from the hash table;
data are interpreted in the same way as described for digest_list_add.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
 .../security/diglim/implementation.rst        |   9 +
 MAINTAINERS                                   |   1 +
 include/linux/kernel_read_file.h              |   1 +
 security/integrity/diglim/Makefile            |   2 +-
 security/integrity/diglim/diglim.h            |   2 +
 security/integrity/diglim/fs.c                | 276 ++++++++++++++++++
 6 files changed, 290 insertions(+), 1 deletion(-)
 create mode 100644 security/integrity/diglim/fs.c

diff --git a/Documentation/security/diglim/implementation.rst b/Documentation/security/diglim/implementation.rst
index 626af0d245ef..f7b48c093f39 100644
--- a/Documentation/security/diglim/implementation.rst
+++ b/Documentation/security/diglim/implementation.rst
@@ -217,3 +217,12 @@ back when one of the steps fails.
 
 #. digest_list_parse() deletes the struct digest_list_item on unsuccessful
    add or successful delete.
+
+
+Interfaces
+----------
+
+This section introduces the interfaces in
+``<securityfs>/integrity/diglim`` necessary to interact with DIGLIM.
+
+.. kernel-doc:: security/integrity/diglim/fs.c
diff --git a/MAINTAINERS b/MAINTAINERS
index f10690dda734..826f628f4fab 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5514,6 +5514,7 @@ F:	Documentation/security/diglim/introduction.rst
 F:	include/linux/diglim.h
 F:	include/uapi/linux/diglim.h
 F:	security/integrity/diglim/diglim.h
+F:	security/integrity/diglim/fs.c
 F:	security/integrity/diglim/ima.c
 F:	security/integrity/diglim/methods.c
 F:	security/integrity/diglim/parser.c
diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
index 575ffa1031d3..636ecdfdc616 100644
--- a/include/linux/kernel_read_file.h
+++ b/include/linux/kernel_read_file.h
@@ -14,6 +14,7 @@
 	id(KEXEC_INITRAMFS, kexec-initramfs)	\
 	id(POLICY, security-policy)		\
 	id(X509_CERTIFICATE, x509-certificate)	\
+	id(DIGEST_LIST, digest-list)	\
 	id(MAX_ID, )
 
 #define __fid_enumify(ENUM, dummy) READING_ ## ENUM,
diff --git a/security/integrity/diglim/Makefile b/security/integrity/diglim/Makefile
index 880dc5300792..5cb1a8bfa0fc 100644
--- a/security/integrity/diglim/Makefile
+++ b/security/integrity/diglim/Makefile
@@ -5,4 +5,4 @@
 
 obj-$(CONFIG_DIGLIM) += diglim.o
 
-diglim-y := methods.o parser.o ima.o
+diglim-y := methods.o parser.o ima.o fs.o
diff --git a/security/integrity/diglim/diglim.h b/security/integrity/diglim/diglim.h
index ebe8936520b5..c597c2e7a52a 100644
--- a/security/integrity/diglim/diglim.h
+++ b/security/integrity/diglim/diglim.h
@@ -227,4 +227,6 @@ int digest_list_parse(loff_t size, void *buf, enum ops op, u8 actions,
 int diglim_ima_get_info(struct file *file, u8 *buffer, size_t buffer_len,
 			char *event_name, u8 *digest, size_t digest_len,
 			enum hash_algo *algo, u8 *actions);
+
+ssize_t digest_list_read(struct path *root, char *path, enum ops op);
 #endif /*__DIGLIM_INTERNAL_H*/
diff --git a/security/integrity/diglim/fs.c b/security/integrity/diglim/fs.c
new file mode 100644
index 000000000000..5698afd2d18a
--- /dev/null
+++ b/security/integrity/diglim/fs.c
@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2005,2006,2007,2008 IBM Corporation
+ * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
+ *
+ * Functions for the interfaces exposed in securityfs.
+ */
+
+#include <linux/fcntl.h>
+#include <linux/kernel_read_file.h>
+#include <linux/module_signature.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/seq_file.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>
+#include <linux/parser.h>
+#include <linux/vmalloc.h>
+#include <linux/namei.h>
+#include <linux/ima.h>
+
+#include "diglim.h"
+
+#define MAX_DIGEST_LIST_SIZE (64 * 1024 * 1024 - 1)
+
+static struct dentry *diglim_dir;
+/**
+ * DOC: digest_list_add
+ *
+ * digest_list_add can be used to upload a digest list and add the digests
+ * to the hash table; passed data are interpreted as file path if the first
+ * byte is ``/`` or as the digest list itself otherwise.
+ *
+ * diglim_ima_get_info() is called to retrieve from IMA the digest of the passed
+ * digest list (file or buffer), and the actions performed (measure/appraise/
+ * appraise with signature).
+ */
+static struct dentry *digest_list_add_dentry;
+/**
+ * DOC: digest_list_del
+ *
+ * digest_list_del can be used to upload a digest list and delete the
+ * digests from the hash table; data are interpreted in the same way as
+ * described for digest_list_add.
+ */
+static struct dentry *digest_list_del_dentry;
+char digest_list_label[NAME_MAX + 1];
+
+/*
+ * check_modsig: detect appended signature
+ */
+static int check_modsig(u8 *buf, size_t buf_len)
+{
+	const size_t marker_len = strlen(MODULE_SIG_STRING);
+	const struct module_signature *sig;
+	size_t sig_len;
+	const void *p;
+
+	if (buf_len <= marker_len + sizeof(*sig))
+		return -ENOENT;
+
+	p = buf + buf_len - marker_len;
+	if (memcmp(p, MODULE_SIG_STRING, marker_len))
+		return -ENOENT;
+
+	sig = (const struct module_signature *)(p - sizeof(*sig));
+	sig_len = be32_to_cpu(sig->sig_len);
+	return marker_len + sig_len + sizeof(*sig);
+}
+
+/*
+ * digest_list_read: read and parse the digest list from the path
+ */
+ssize_t digest_list_read(struct path *root, char *path, enum ops op)
+{
+	void *data = NULL;
+	char *datap;
+	size_t size;
+	u8 actions = 0;
+	struct file *file;
+	char event_name[NAME_MAX + 9 + 1];
+	u8 digest[IMA_MAX_DIGEST_SIZE] = { 0 };
+	enum hash_algo algo;
+	int rc, pathlen = strlen(path);
+
+	/* Remove \n. */
+	datap = path;
+	strsep(&datap, "\n");
+
+	if (root)
+		file = file_open_root(root, path, O_RDONLY, 0);
+	else
+		file = filp_open(path, O_RDONLY, 0);
+	if (IS_ERR(file)) {
+		pr_err("unable to open file: %s (%ld)", path, PTR_ERR(file));
+		return PTR_ERR(file);
+	}
+
+	/* Deny writes to the file to obtain stable information from IMA. */
+	rc = deny_write_access(file);
+	if (rc < 0) {
+		pr_err("unable to deny write access to file: %s (%d)", path,
+			rc);
+		goto out;
+	}
+
+	rc = kernel_read_file(file, 0, &data, INT_MAX, NULL,
+			      READING_DIGEST_LIST);
+	if (rc < 0) {
+		pr_err("unable to read file: %s (%d)", path, rc);
+		goto out_allow_write;
+	}
+
+	size = rc;
+	rc = check_modsig(data, size);
+	if (rc > 0)
+		size -= rc;
+
+	snprintf(event_name, sizeof(event_name), "%s_file_%s",
+		 op == DIGEST_LIST_ADD ? "add" : "del",
+		 file_dentry(file)->d_name.name);
+
+	rc = diglim_ima_get_info(file, data, size, event_name, digest,
+				 sizeof(digest), &algo, &actions);
+	if (rc < 0) {
+		pr_err("unable to retrieve IMA info for %s (%d)\n", path, rc);
+		goto out_vfree;
+	}
+
+	rc = digest_list_parse(size, data, op, actions, digest, algo, "");
+	if (rc < 0 && rc != -EEXIST)
+		pr_err("unable to upload digest list %s (%d)\n", path, rc);
+out_vfree:
+	vfree(data);
+out_allow_write:
+	allow_write_access(file);
+out:
+	fput(file);
+
+	if (rc < 0)
+		return rc;
+
+	return pathlen;
+}
+
+/*
+ * digest_list_write: write the digest list path or the digest list itself
+ */
+static ssize_t digest_list_write(struct file *file, const char __user *buf,
+				 size_t datalen, loff_t *ppos)
+{
+	char *data;
+	char *digest_list_label_ptr;
+	ssize_t result;
+	enum ops op = DIGEST_LIST_ADD;
+	struct dentry *dentry = file_dentry(file);
+	u8 digest[IMA_MAX_DIGEST_SIZE];
+	char event_name[NAME_MAX + 11 + 1];
+	enum hash_algo algo;
+	u8 actions = 0;
+
+	/* No partial writes. */
+	result = -EINVAL;
+	if (*ppos != 0)
+		goto out;
+
+	result = -EFBIG;
+	if (datalen > MAX_DIGEST_LIST_SIZE)
+		goto out;
+
+	data = memdup_user_nul(buf, datalen);
+	if (IS_ERR(data)) {
+		result = PTR_ERR(data);
+		goto out;
+	}
+
+	if (dentry == digest_list_del_dentry)
+		op = DIGEST_LIST_DEL;
+
+	result = -EPERM;
+
+	if (data[0] == '/') {
+		result = digest_list_read(NULL, data, op);
+	} else {
+		/* Remove \n. */
+		digest_list_label_ptr = digest_list_label;
+		strsep(&digest_list_label_ptr, "\n");
+
+		snprintf(event_name, sizeof(event_name), "%s_buffer_%s",
+			 op == DIGEST_LIST_ADD ? "add" : "del",
+			 digest_list_label);
+
+		result = diglim_ima_get_info(NULL, data, datalen, event_name,
+					     digest, sizeof(digest), &algo,
+					     &actions);
+		if (result < 0) {
+			pr_err("unable to retrieve IMA info for buffer (%ld)\n",
+			       result);
+			goto out_kfree;
+		}
+
+		memset(digest_list_label, 0, sizeof(digest_list_label));
+
+		result = digest_list_parse(datalen, data, op, actions, digest,
+					   algo, "");
+		if (result < 0 && result != -EEXIST)
+			pr_err("unable to upload generated digest list\n");
+	}
+out_kfree:
+	kfree(data);
+out:
+	return result;
+}
+
+static unsigned long flags;
+
+/*
+ * digest_list_open: sequentialize access to the add/del files
+ */
+static int digest_list_open(struct inode *inode, struct file *filp)
+{
+	if ((filp->f_flags & O_ACCMODE) != O_WRONLY)
+		return -EACCES;
+
+	if (test_and_set_bit(0, &flags))
+		return -EBUSY;
+
+	return 0;
+}
+
+/*
+ * digest_list_release - release the add/del files
+ */
+static int digest_list_release(struct inode *inode, struct file *file)
+{
+	clear_bit(0, &flags);
+	return 0;
+}
+
+static const struct file_operations digest_list_upload_ops = {
+	.open = digest_list_open,
+	.write = digest_list_write,
+	.read = seq_read,
+	.release = digest_list_release,
+	.llseek = generic_file_llseek,
+};
+
+static int __init diglim_fs_init(void)
+{
+	diglim_dir = securityfs_create_dir("diglim", integrity_dir);
+	if (IS_ERR(diglim_dir))
+		return -1;
+
+	digest_list_add_dentry = securityfs_create_file("digest_list_add", 0200,
+						diglim_dir, NULL,
+						&digest_list_upload_ops);
+	if (IS_ERR(digest_list_add_dentry))
+		goto out;
+
+	digest_list_del_dentry = securityfs_create_file("digest_list_del", 0200,
+						diglim_dir, NULL,
+						&digest_list_upload_ops);
+	if (IS_ERR(digest_list_del_dentry))
+		goto out;
+
+	return 0;
+out:
+	securityfs_remove(digest_list_del_dentry);
+	securityfs_remove(digest_list_add_dentry);
+	securityfs_remove(diglim_dir);
+	return -1;
+}
+
+late_initcall(diglim_fs_init);
-- 
2.25.1