Thread (38 messages) 38 messages, 9 authors, 2017-05-05

Re: [PATCH v3 2/2] modules:capabilities: add a per-task modules autoload restriction

From: Djalal Harouni <hidden>
Date: 2017-04-19 22:39:06
Also in: linux-security-module, lkml

On Thu, Apr 20, 2017 at 12:20 AM, Djalal Harouni [off-list ref] wrote:
[...]
+/* Returns task's modules_autoload */
+static inline void task_copy_modules_autoload(struct task_struct *dest,
+                                             struct task_struct *src)
+{
+       dest->modules_autoload = src->modules_autoload;
+}
Kees Cook just pointed out that this hook is not needed since we
already dup everything from parent to child.


[...]
quoted hunk ↗ jump to hunk
diff --git a/include/linux/security.h b/include/linux/security.h
index e274bb11..9581cc5 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -866,7 +866,7 @@ static inline int security_task_create(unsigned long clone_flags)
 static inline int security_task_alloc(struct task_struct *task,
                                      unsigned long clone_flags)
 {
-       return 0;
+       return cap_task_alloc(task, clone_flags);
 }
Will remove it in next iteration.

quoted hunk ↗ jump to hunk
 static inline void security_task_free(struct task_struct *task)
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index a8d0759..0244264 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -197,4 +197,12 @@ struct prctl_mm_map {
 # define PR_CAP_AMBIENT_LOWER          3
 # define PR_CAP_AMBIENT_CLEAR_ALL      4

+/*
+ * Control the per-task "modules_autoload" access.
+ *
+ * See Documentation/prctl/modules_autoload.txt for more details.
+ */
+#define PR_SET_MODULES_AUTOLOAD                48
+#define PR_GET_MODULES_AUTOLOAD                49
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 81347bd..141e06b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1695,6 +1695,10 @@ static __latent_entropy struct task_struct *copy_process(
        p->sequential_io_avg    = 0;
 #endif

+#ifdef CONFIG_MODULES
+       p->modules_autoload     = 0;
+#endif
+
        /* Perform scheduler related setup. Assign this task to a CPU. */
        retval = sched_fork(clone_flags, p);
        if (retval)
diff --git a/kernel/module.c b/kernel/module.c
index 54cb6e0..e1eca74 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4313,19 +4313,24 @@ static int modules_autoload_privileged_access(const char *name)
 }

 /**
- * modules_autoload_access - Determine whether a module auto-load is permitted
+ * modules_autoload_access - Determine whether the task is allowed to perform a
+ *                          module auto-load request
+ * @task: The task performing the request
  * @kmod_name: The module name
  *
- * Determine whether a module should be automatically loaded or not. The check
- * uses the sysctl "modules_autoload" value.
+ * Determine whether the task is allowed to perform a module auto-load request.
+ * This checks the per-task "modules_autoload" flag, if the access is not denied,
+ * then the global sysctl "modules_autoload" is evaluated.
  *
  * Returns 0 if the module request is allowed or -EPERM if not.
  */
-int modules_autoload_access(char *kmod_name)
+int modules_autoload_access(struct task_struct *task, char *kmod_name)
 {
-       if (modules_autoload == MODULES_AUTOLOAD_ALLOWED)
+       unsigned int autoload = max_t(unsigned int,
+                                     modules_autoload, task->modules_autoload);
+       if (autoload == MODULES_AUTOLOAD_ALLOWED)
                return 0;
-       else if (modules_autoload == MODULES_AUTOLOAD_PRIVILEGED)
+       else if (autoload == MODULES_AUTOLOAD_PRIVILEGED)
                return modules_autoload_privileged_access(kmod_name);

        /* MODULES_AUTOLOAD_DISABLED */
diff --git a/security/commoncap.c b/security/commoncap.c
index 67a6cfe..bcc1e09 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -886,6 +886,40 @@ static int cap_prctl_drop(unsigned long cap)
        return commit_creds(new);
 }

+static int pr_set_mod_autoload(unsigned long arg2, unsigned long arg3,
+                              unsigned long arg4, unsigned long arg5)
+{
+       if (arg3 || arg4 || arg5)
+               return -EINVAL;
+
+       return task_set_modules_autoload(current, arg2);
+}
+
+static inline int pr_get_mod_autoload(unsigned long arg2, unsigned long arg3,
+                                     unsigned long arg4, unsigned long arg5)
+{
+       if (arg2 || arg3 || arg4 || arg5)
+               return -EINVAL;
+
+       return task_modules_autoload(current);
+}
+
+/**
+ * cap_task_alloc - Implement process context allocation for this security module
+ * @task: task being allocated
+ * @clone_flags: contains the clone flags indicating what should be shared.
+ *
+ * Allocate or initialize the task context for this security module.
+ *
+ * Returns 0.
+ */
+int cap_task_alloc(struct task_struct *task, unsigned long clone_flags)
+{
+       task_copy_modules_autoload(task, current);
+
+       return 0;
+}
All the calls to initialize task->modules_autoload or dup its value
using the task_alloc will be removed in next iteration as pointed out
by Kees.

Thanks!

-- 
tixxdz
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