[PATCH 2/2] module: restrict autoload to CAP_SYS_ADMIN if CONFIG_MODULE_RESTRICT_AUTOLOAD

[Michal Gorlas <michal.gorlas@9elements.com>]

Restrict module auto-loading to CAP_SYS_ADMIN if
CONFIG_MODULE_RESTRICT_AUTOLOAD is enabled, cmdline parameter
modrestrict=true, or kernel.modrestrict=1 is set with sysctl.

Signed-off-by: Michal Gorlas <michal.gorlas@9elements.com>
---
 kernel/module/internal.h |  1 +
 kernel/module/kmod.c     |  5 +++++
 kernel/module/main.c     | 11 +++++++++++
 3 files changed, 17 insertions(+)

diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 061161cc79d9..496d8703f0c6 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -46,6 +46,7 @@ struct kernel_symbol {
 
 extern struct mutex module_mutex;
 extern struct list_head modules;
+extern bool module_autoload_restrict;
 
 extern const struct module_attribute *const modinfo_attrs[];
 extern const size_t modinfo_attrs_count;
diff --git a/kernel/module/kmod.c b/kernel/module/kmod.c
index a25dccdf7aa7..58b28c23f571 100644
--- a/kernel/module/kmod.c
+++ b/kernel/module/kmod.c
@@ -156,6 +156,11 @@ int __request_module(bool wait, const char *fmt, ...)
 	if (ret)
 		return ret;
 
+	if (module_autoload_restrict && !capable(CAP_SYS_ADMIN)) {
+		pr_alert("denied attempt to auto-load module %s\n", module_name);
+		return -EPERM;
+	}
+
 	ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
 	if (ret) {
 		pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 46dd8d25a605..a293b75ce9b7 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -130,6 +130,10 @@ static void mod_update_bounds(struct module *mod)
 static int modules_disabled;
 core_param(nomodule, modules_disabled, bint, 0);
 
+/* Restrict auto-loading? */
+bool module_autoload_restrict = IS_ENABLED(CONFIG_MODULE_RESTRICT_AUTOLOAD);
+core_param(modrestrict, module_autoload_restrict, bool, 0);
+
 static const struct ctl_table module_sysctl_table[] = {
 	{
 		.procname	= "modprobe",
@@ -148,6 +152,13 @@ static const struct ctl_table module_sysctl_table[] = {
 		.extra1		= SYSCTL_ONE,
 		.extra2		= SYSCTL_ONE,
 	},
+	{
+		.procname	= "modrestrict",
+		.data		= &module_autoload_restrict,
+		.maxlen		= sizeof(bool),
+		.mode		= 0644,
+		.proc_handler   = proc_dobool,
+	},
 };
 
 static int __init init_module_sysctl(void)

-- 
2.54.0