[PATCH v5 next 3/5] modules:capabilities: automatic module loading restriction

On Thu, Nov 30, 2017 at 2:23 AM, Luis R. Rodriguez [off-list ref] wrote:

On Mon, Nov 27, 2017 at 06:18:36PM +0100, Djalal Harouni wrote:

quoted

diff --git a/include/linux/module.h b/include/linux/module.h
index 5cbb239..c36aed8 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h

@@ -261,7 +261,16 @@ struct notifier_block;

 #ifdef CONFIG_MODULES

-extern int modules_disabled; /* for sysctl */
+enum {
+     MODULES_AUTOLOAD_ALLOWED        = 0,
+     MODULES_AUTOLOAD_PRIVILEGED     = 1,
+     MODULES_AUTOLOAD_DISABLED       = 2,
+};
+

Can you kdocify these and add a respective rst doc file?  Maybe stuff your
extensive docs which you are currently adding to
Documentation/sysctl/kernel.txt to this new file and in kernel.txt just refer
to it. This way this can be also nicely visibly documented on the web with the
new sphinx.

This way you can take advantage of the kdocs you are already adding and refer
to them.

Alright I'll do it in the next series next week, we'll change the
semantics as requested by Linus and Kees here:
http://www.openwall.com/lists/kernel-hardening/2017/11/29/38

To block the privilege escalation through the usermod helper.

quoted

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 2fb4e27..0b6f0c8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c

@@ -683,6 +688,15 @@ static struct ctl_table kern_table[] = {
              .extra1         = &one,
              .extra2         = &one,
      },
+     {
+             .procname       = "modules_autoload_mode",
+             .data           = &modules_autoload_mode,
+             .maxlen         = sizeof(int),
+             .mode           = 0644,
+             .proc_handler   = modules_autoload_dointvec_minmax,

It would seem this is a unint ... so why not reflect that?

quoted

@@ -2499,6 +2513,20 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
 }
 #endif

+#ifdef CONFIG_MODULES
+static int modules_autoload_dointvec_minmax(struct ctl_table *table, int write,
+                             void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+     /*
+      * Only CAP_SYS_MODULE in init user namespace are allowed to change this
+      */
+     if (write && !capable(CAP_SYS_MODULE))
+             return -EPERM;
+
+     return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+}
+#endif

We now have proc_douintvec_minmax().

Yes, however in that same response by Linus it was suggested to drop
the sysctl completely, so next iterations will not have this code.

Thank you for the review!

-- 
tixxdz
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