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- // SPDX-License-Identifier: GPL-2.0-only
- /*
- * Module and Firmware Pinning Security Module
- *
- * Copyright 2011-2016 Google Inc.
- *
- * Author: Kees Cook <[email protected]>
- */
- #define pr_fmt(fmt) "LoadPin: " fmt
- #include <linux/module.h>
- #include <linux/fs.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>
- #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
- #ifdef CONFIG_SYSCTL
- static struct ctl_path loadpin_sysctl_path[] = {
- { .procname = "kernel", },
- { .procname = "loadpin", },
- { }
- };
- static struct ctl_table loadpin_sysctl_table[] = {
- {
- .procname = "enforce",
- .data = &enforce,
- .maxlen = sizeof(int),
- .mode = 0644,
- .proc_handler = proc_dointvec_minmax,
- .extra1 = SYSCTL_ZERO,
- .extra2 = SYSCTL_ONE,
- },
- { }
- };
- /*
- * This must be called after early kernel init, since then the rootdev
- * is available.
- */
- static void check_pinning_enforcement(struct super_block *mnt_sb)
- {
- bool ro = false;
- /*
- * If load pinning is not enforced via a read-only block
- * device, allow sysctl to change modes for testing.
- */
- if (mnt_sb->s_bdev) {
- ro = bdev_read_only(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),
- ro ? "read-only" : "writable");
- } else
- pr_info("mnt_sb lacks block device, treating as: writable\n");
- if (!ro) {
- if (!register_sysctl_paths(loadpin_sysctl_path,
- loadpin_sysctl_table))
- pr_notice("sysctl registration failed!\n");
- else
- pr_info("enforcement can be disabled.\n");
- } else
- pr_info("load pinning engaged.\n");
- }
- #else
- static void check_pinning_enforcement(struct super_block *mnt_sb)
- {
- pr_info("load pinning engaged.\n");
- }
- #endif
- 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.
- */
- if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
- pinned_root = ERR_PTR(-EIO);
- pr_info("umount pinned fs: refusing further loads\n");
- }
- }
- 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);
- /* 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. Otherwise, it is either
- * a valid reference, or an ERR_PTR.
- */
- if (!pinned_root) {
- pinned_root = load_root;
- /*
- * Unlock now since it's only pinned_root we care about.
- * In the worst case, we will (correctly) report pinning
- * failures before we have announced that pinning is
- * enforcing. This would be purely cosmetic.
- */
- spin_unlock(&pinned_root_spinlock);
- check_pinning_enforcement(pinned_root);
- report_load(origin, file, "pinned");
- } else {
- spin_unlock(&pinned_root_spinlock);
- }
- 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 struct security_hook_list loadpin_hooks[] __lsm_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();
- security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
- return 0;
- }
- DEFINE_LSM(loadpin) = {
- .name = "loadpin",
- .init = loadpin_init,
- };
- #ifdef CONFIG_SECURITY_LOADPIN_VERITY
- enum loadpin_securityfs_interface_index {
- LOADPIN_DM_VERITY,
- };
- static int read_trusted_verity_root_digests(unsigned int fd)
- {
- struct fd f;
- 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;
- f = fdget(fd);
- if (!f.file)
- return -EINVAL;
- data = kzalloc(SZ_4K, GFP_KERNEL);
- if (!data) {
- rc = -ENOMEM;
- goto err;
- }
- rc = kernel_read_file(f.file, 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(struct_size(trd, data, len), GFP_KERNEL);
- if (!trd) {
- rc = -ENOMEM;
- goto err;
- }
- if (hex2bin(trd->data, d, len)) {
- kfree(trd);
- rc = -EPROTO;
- goto err;
- }
- trd->len = len;
- 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);
- fdput(f);
- 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;
- fdput(f);
- 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;
- }
- fs_initcall(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");
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