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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