// 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");