RE: [PATCH] clone3: validate stack arguments

From Christian Brauner
Sent: 31 October 2019 11:36

Validate the stack arguments and setup the stack depening on whether or not
it is growing down or up.

...

-static bool clone3_args_valid(const struct kernel_clone_args *kargs)
+/**
+ * clone3_stack_valid - check and prepare stack
+ * @kargs: kernel clone args
+ *
+ * Verify that the stack arguments userspace gave us are sane.
+ * In addition, set the stack direction for userspace since it's easy for us to
+ * determine.
+ */
+static inline bool clone3_stack_valid(struct kernel_clone_args *kargs)
+{
+	if (kargs->stack == 0) {
+		if (kargs->stack_size > 0)
+			return false;
+	} else {
+		if (kargs->stack_size == 0)
+			return false;
+
+		if (!access_ok((void __user *)kargs->stack, kargs->stack_size))
+			return false;

Does access_ok() do anything useful here?
It only verifies that the buffer isn't in kernel space.

	David

-
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