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authorKees Cook <keescook@chromium.org>2016-04-20 15:46:28 -0700
committerJames Morris <james.l.morris@oracle.com>2016-04-21 10:47:27 +1000
commit9b091556a073a9f5f93e2ad23d118f45c4796a84 (patch)
tree075fffff80b5caad9738f633c83333dea9e04efd /security/loadpin
parent1284ab5b2dcb927d38e4f3fbc2e307f3d1af9262 (diff)
LSM: LoadPin for kernel file loading restrictions
This LSM enforces that kernel-loaded files (modules, firmware, etc) must all come from the same filesystem, with the expectation that such a filesystem is backed by a read-only device such as dm-verity or CDROM. This allows systems that have a verified and/or unchangeable filesystem to enforce module and firmware loading restrictions without needing to sign the files individually. Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
Diffstat (limited to 'security/loadpin')
-rw-r--r--security/loadpin/Kconfig10
-rw-r--r--security/loadpin/Makefile1
-rw-r--r--security/loadpin/loadpin.c190
3 files changed, 201 insertions, 0 deletions
diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig
new file mode 100644
index 000000000000..c668ac4eda65
--- /dev/null
+++ b/security/loadpin/Kconfig
@@ -0,0 +1,10 @@
+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) will
+ be pinned to the first filesystem used for loading. 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.
diff --git a/security/loadpin/Makefile b/security/loadpin/Makefile
new file mode 100644
index 000000000000..c2d77f83037b
--- /dev/null
+++ b/security/loadpin/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SECURITY_LOADPIN) += loadpin.o
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
new file mode 100644
index 000000000000..e4debae3c4d6
--- /dev/null
+++ b/security/loadpin/loadpin.c
@@ -0,0 +1,190 @@
+/*
+ * Module and Firmware Pinning Security Module
+ *
+ * Copyright 2011-2016 Google Inc.
+ *
+ * Author: Kees Cook <keescook@chromium.org>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#define pr_fmt(fmt) "LoadPin: " fmt
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/fs_struct.h>
+#include <linux/lsm_hooks.h>
+#include <linux/mount.h>
+#include <linux/path.h>
+#include <linux/sched.h> /* current */
+#include <linux/string_helpers.h>
+
+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 enabled = 1;
+static struct super_block *pinned_root;
+static DEFINE_SPINLOCK(pinned_root_spinlock);
+
+#ifdef CONFIG_SYSCTL
+static int zero;
+static int one = 1;
+
+static struct ctl_path loadpin_sysctl_path[] = {
+ { .procname = "kernel", },
+ { .procname = "loadpin", },
+ { }
+};
+
+static struct ctl_table loadpin_sysctl_table[] = {
+ {
+ .procname = "enabled",
+ .data = &enabled,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &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("dev(%u,%u): %s\n",
+ 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("load pinning 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_read_file(struct file *file, enum kernel_read_file_id id)
+{
+ struct super_block *load_root;
+ const char *origin = kernel_read_file_id_str(id);
+
+ /* This handles the older init_module API that has a NULL file. */
+ if (!file) {
+ if (!enabled) {
+ 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
+ * enabled. 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) {
+ if (unlikely(!enabled)) {
+ report_load(origin, file, "pinning-ignored");
+ return 0;
+ }
+
+ report_load(origin, file, "denied");
+ return -EPERM;
+ }
+
+ return 0;
+}
+
+static struct security_hook_list loadpin_hooks[] = {
+ LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
+ LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
+};
+
+void __init loadpin_add_hooks(void)
+{
+ pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis");
+ security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks));
+}
+
+/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
+module_param(enabled, int, 0);
+MODULE_PARM_DESC(enabled, "Pin module/firmware loading (default: true)");

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