Resguardo inicial

linux-7.2.3/security/loadpin/Kconfig

@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config SECURITY_LOADPIN
+	bool "Pin load of kernel files (modules, fw, etc) to one filesystem"
+	depends on SECURITY && BLOCK
+	help
+	  Any files read through the kernel file reading interface
+	  (kernel modules, firmware, kexec images, security policy)
+	  can be pinned to the first filesystem used for loading. When
+	  enabled, any files that come from other filesystems will be
+	  rejected. This is best used on systems without an initrd that
+	  have a root filesystem backed by a read-only device such as
+	  dm-verity or a CDROM.
+
+config SECURITY_LOADPIN_ENFORCE
+	bool "Enforce LoadPin at boot"
+	depends on SECURITY_LOADPIN
+	# Module compression breaks LoadPin unless modules are decompressed in
+	# the kernel.
+	depends on !MODULE_COMPRESS || MODULE_DECOMPRESS
+	help
+	  If selected, LoadPin will enforce pinning at boot. If not
+	  selected, it can be enabled at boot with the kernel parameter
+	  "loadpin.enforce=1".
+
+config SECURITY_LOADPIN_VERITY
+	bool "Allow reading files from certain other filesystems that use dm-verity"
+	depends on SECURITY_LOADPIN && DM_VERITY=y && SECURITYFS
+	help
+	  If selected LoadPin can allow reading files from filesystems
+	  that use dm-verity. LoadPin maintains a list of verity root
+	  digests it considers trusted. A verity backed filesystem is
+	  considered trusted if its root digest is found in the list
+	  of trusted digests.
+
+	  The list of trusted verity can be populated through an ioctl
+	  on the LoadPin securityfs entry 'dm-verity'. The ioctl
+	  expects a file descriptor of a file with verity digests as
+	  parameter. The file must be located on the pinned root and
+	  start with the line:
+
+	  # LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS
+
+	  This is followed by the verity digests, with one digest per
+	  line.

linux-7.2.3/security/loadpin/Makefile

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SECURITY_LOADPIN) += loadpin.o

linux-7.2.3/security/loadpin/loadpin.c

@@ -0,0 +1,442 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Module and Firmware Pinning Security Module
+ *
+ * Copyright 2011-2016 Google Inc.
+ *
+ * Author: Kees Cook <keescook@chromium.org>
+ */
+
+#define pr_fmt(fmt) "LoadPin: " fmt
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/hex.h>
+#include <linux/kernel_read_file.h>
+#include <linux/lsm_hooks.h>
+#include <linux/mount.h>
+#include <linux/blkdev.h>
+#include <linux/path.h>
+#include <linux/sched.h>	/* current */
+#include <linux/string_helpers.h>
+#include <linux/dm-verity-loadpin.h>
+#include <uapi/linux/loadpin.h>
+#include <uapi/linux/lsm.h>
+
+#define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS"
+
+static void report_load(const char *origin, struct file *file, char *operation)
+{
+	char *cmdline, *pathname;
+
+	pathname = kstrdup_quotable_file(file, GFP_KERNEL);
+	cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
+
+	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
+		  origin, operation,
+		  (pathname && pathname[0] != '<') ? "\"" : "",
+		  pathname,
+		  (pathname && pathname[0] != '<') ? "\"" : "",
+		  task_pid_nr(current),
+		  cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
+
+	kfree(cmdline);
+	kfree(pathname);
+}
+
+static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
+static char *exclude_read_files[READING_MAX_ID];
+static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
+static struct super_block *pinned_root;
+static DEFINE_SPINLOCK(pinned_root_spinlock);
+#ifdef CONFIG_SECURITY_LOADPIN_VERITY
+static bool deny_reading_verity_digests;
+#endif
+
+// initialized to false
+static bool loadpin_root_writable;
+#ifdef CONFIG_SYSCTL
+
+static int proc_handler_loadpin(const struct ctl_table *table, int dir,
+				void *buffer, size_t *lenp, loff_t *ppos)
+{
+	if (!loadpin_root_writable && SYSCTL_USER_TO_KERN(dir))
+		return -EINVAL;
+	return proc_dointvec_minmax(table, dir, buffer, lenp, ppos);
+}
+
+static const struct ctl_table loadpin_sysctl_table[] = {
+	{
+		.procname       = "enforce",
+		.data           = &enforce,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_handler_loadpin,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = SYSCTL_ONE,
+	},
+};
+#endif
+
+static void report_writable(struct super_block *mnt_sb, bool writable)
+{
+	if (mnt_sb->s_bdev) {
+		pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
+			MAJOR(mnt_sb->s_bdev->bd_dev),
+			MINOR(mnt_sb->s_bdev->bd_dev),
+			writable ? "writable" : "read-only");
+	} else
+		pr_info("mnt_sb lacks block device, treating as: writable\n");
+
+	if (!writable)
+		pr_info("load pinning engaged.\n");
+}
+
+/*
+ * This must be called after early kernel init, since then the rootdev
+ * is available.
+ */
+static bool sb_is_writable(struct super_block *mnt_sb)
+{
+	bool writable = true;
+
+	if (mnt_sb->s_bdev)
+		writable = !bdev_read_only(mnt_sb->s_bdev);
+
+	return writable;
+}
+
+static void loadpin_sb_free_security(struct super_block *mnt_sb)
+{
+	/*
+	 * When unmounting the filesystem we were using for load
+	 * pinning, we acknowledge the superblock release, but make sure
+	 * no other modules or firmware can be loaded when we are in
+	 * enforcing mode. Otherwise, allow the root to be reestablished.
+	 */
+	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
+		if (enforce) {
+			pinned_root = ERR_PTR(-EIO);
+			pr_info("umount pinned fs: refusing further loads\n");
+		} else {
+			pinned_root = NULL;
+		}
+	}
+}
+
+static int loadpin_check(struct file *file, enum kernel_read_file_id id)
+{
+	struct super_block *load_root;
+	const char *origin = kernel_read_file_id_str(id);
+	bool first_root_pin = false;
+
+	/* If the file id is excluded, ignore the pinning. */
+	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
+	    ignore_read_file_id[id]) {
+		report_load(origin, file, "pinning-excluded");
+		return 0;
+	}
+
+	/* This handles the older init_module API that has a NULL file. */
+	if (!file) {
+		if (!enforce) {
+			report_load(origin, NULL, "old-api-pinning-ignored");
+			return 0;
+		}
+
+		report_load(origin, NULL, "old-api-denied");
+		return -EPERM;
+	}
+
+	load_root = file->f_path.mnt->mnt_sb;
+
+	/* First loaded module/firmware defines the root for all others. */
+	spin_lock(&pinned_root_spinlock);
+	/*
+	 * pinned_root is only NULL at startup or when the pinned root has
+	 * been unmounted while we are not in enforcing mode. Otherwise, it
+	 * is either a valid reference, or an ERR_PTR.
+	 */
+	if (!pinned_root) {
+		pinned_root = load_root;
+		first_root_pin = true;
+	}
+	spin_unlock(&pinned_root_spinlock);
+
+	if (first_root_pin) {
+		loadpin_root_writable = sb_is_writable(pinned_root);
+		report_writable(pinned_root, loadpin_root_writable);
+		report_load(origin, file, "pinned");
+	}
+
+	if (IS_ERR_OR_NULL(pinned_root) ||
+	    ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
+		if (unlikely(!enforce)) {
+			report_load(origin, file, "pinning-ignored");
+			return 0;
+		}
+
+		report_load(origin, file, "denied");
+		return -EPERM;
+	}
+
+	return 0;
+}
+
+static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
+			     bool contents)
+{
+	/*
+	 * LoadPin only cares about the _origin_ of a file, not its
+	 * contents, so we can ignore the "are full contents available"
+	 * argument here.
+	 */
+	return loadpin_check(file, id);
+}
+
+static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
+{
+	/*
+	 * LoadPin only cares about the _origin_ of a file, not its
+	 * contents, so a NULL file is passed, and we can ignore the
+	 * state of "contents".
+	 */
+	return loadpin_check(NULL, (enum kernel_read_file_id) id);
+}
+
+static const struct lsm_id loadpin_lsmid = {
+	.name = "loadpin",
+	.id = LSM_ID_LOADPIN,
+};
+
+static struct security_hook_list loadpin_hooks[] __ro_after_init = {
+	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
+	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
+	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
+};
+
+static void __init parse_exclude(void)
+{
+	int i, j;
+	char *cur;
+
+	/*
+	 * Make sure all the arrays stay within expected sizes. This
+	 * is slightly weird because kernel_read_file_str[] includes
+	 * READING_MAX_ID, which isn't actually meaningful here.
+	 */
+	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
+		     ARRAY_SIZE(ignore_read_file_id));
+	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
+		     ARRAY_SIZE(ignore_read_file_id));
+
+	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
+		cur = exclude_read_files[i];
+		if (!cur)
+			break;
+		if (*cur == '\0')
+			continue;
+
+		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
+			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
+				pr_info("excluding: %s\n",
+					kernel_read_file_str[j]);
+				ignore_read_file_id[j] = 1;
+				/*
+				 * Can not break, because one read_file_str
+				 * may map to more than on read_file_id.
+				 */
+			}
+		}
+	}
+}
+
+static int __init loadpin_init(void)
+{
+	pr_info("ready to pin (currently %senforcing)\n",
+		enforce ? "" : "not ");
+	parse_exclude();
+#ifdef CONFIG_SYSCTL
+	if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table))
+		pr_notice("sysctl registration failed!\n");
+#endif
+	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
+			   &loadpin_lsmid);
+
+	return 0;
+}
+
+#ifdef CONFIG_SECURITY_LOADPIN_VERITY
+
+enum loadpin_securityfs_interface_index {
+	LOADPIN_DM_VERITY,
+};
+
+static int read_trusted_verity_root_digests(unsigned int fd)
+{
+	void *data;
+	int rc;
+	char *p, *d;
+
+	if (deny_reading_verity_digests)
+		return -EPERM;
+
+	/* The list of trusted root digests can only be set up once */
+	if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
+		return -EPERM;
+
+	CLASS(fd, f)(fd);
+	if (fd_empty(f))
+		return -EINVAL;
+
+	data = kzalloc(SZ_4K, GFP_KERNEL);
+	if (!data) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	rc = kernel_read_file(fd_file(f), 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
+	if (rc < 0)
+		goto err;
+
+	p = data;
+	p[rc] = '\0';
+	p = strim(p);
+
+	p = strim(data);
+	while ((d = strsep(&p, "\n")) != NULL) {
+		int len;
+		struct dm_verity_loadpin_trusted_root_digest *trd;
+
+		if (d == data) {
+			/* first line, validate header */
+			if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
+				rc = -EPROTO;
+				goto err;
+			}
+
+			continue;
+		}
+
+		len = strlen(d);
+
+		if (len % 2) {
+			rc = -EPROTO;
+			goto err;
+		}
+
+		len /= 2;
+
+		trd = kzalloc_flex(*trd, data, len);
+		if (!trd) {
+			rc = -ENOMEM;
+			goto err;
+		}
+		trd->len = len;
+
+		if (hex2bin(trd->data, d, len)) {
+			kfree(trd);
+			rc = -EPROTO;
+			goto err;
+		}
+
+		list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
+	}
+
+	if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
+		rc = -EPROTO;
+		goto err;
+	}
+
+	kfree(data);
+
+	return 0;
+
+err:
+	kfree(data);
+
+	/* any failure in loading/parsing invalidates the entire list */
+	{
+		struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
+
+		list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
+			list_del(&trd->node);
+			kfree(trd);
+		}
+	}
+
+	/* disallow further attempts after reading a corrupt/invalid file */
+	deny_reading_verity_digests = true;
+
+	return rc;
+}
+
+/******************************** securityfs ********************************/
+
+static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	void __user *uarg = (void __user *)arg;
+	unsigned int fd;
+
+	switch (cmd) {
+	case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
+		if (copy_from_user(&fd, uarg, sizeof(fd)))
+			return -EFAULT;
+
+		return read_trusted_verity_root_digests(fd);
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct file_operations loadpin_dm_verity_ops = {
+	.unlocked_ioctl = dm_verity_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+};
+
+/**
+ * init_loadpin_securityfs - create the securityfs directory for LoadPin
+ *
+ * We can not put this method normally under the loadpin_init() code path since
+ * the security subsystem gets initialized before the vfs caches.
+ *
+ * Returns 0 if the securityfs directory creation was successful.
+ */
+static int __init init_loadpin_securityfs(void)
+{
+	struct dentry *loadpin_dir, *dentry;
+
+	loadpin_dir = securityfs_create_dir("loadpin", NULL);
+	if (IS_ERR(loadpin_dir)) {
+		pr_err("LoadPin: could not create securityfs dir: %ld\n",
+		       PTR_ERR(loadpin_dir));
+		return PTR_ERR(loadpin_dir);
+	}
+
+	dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
+					(void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
+	if (IS_ERR(dentry)) {
+		pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
+		       PTR_ERR(dentry));
+		return PTR_ERR(dentry);
+	}
+
+	return 0;
+}
+
+#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
+
+DEFINE_LSM(loadpin) = {
+	.id = &loadpin_lsmid,
+	.init = loadpin_init,
+#ifdef CONFIG_SECURITY_LOADPIN_VERITY
+	.initcall_fs = init_loadpin_securityfs,
+#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
+};
+
+/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
+module_param(enforce, int, 0);
+MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
+module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
+MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");