Re: [PATCH] misc: sgi-gru: fix use-after-free error in gru_set_context_option, gru_fault and gru_handle_user_call_os

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Sep 19, 2022 at 10:32:05PM +0800, Zheng Wang wrote:
> In grufile.c, gru_file_unlocked_ioctl function can be called by user.
> 
> If the req is GRU_SET_CONTEXT_OPTION, it will call gru_set_context_option.
> 
> In gru_set_context_option, as req can be controlled by user,
> 
> We can reach gru_check_context_placement function call.
> 
> In gru_check_context_placement function, if the error path was steped,
> 
> say gru_check_chiplet_assignment return 0,
> 
> Then it will fall into gru_unload_context function.
> 
> And it will finnaly call kfree gts in gts_drop function.
> 
> Then gru_unlock_gts will be called in gru_set_context_option function.
> 
> This is a typical Use after free.
> 
> The same problem exists in gru_handle_user_call_os and gru_fault.
> 
> Fix it by introduce the return value to see if gts is in good case or not.
> 
> Free the gts in caller when gru_check_chiplet_assignment check failed.

Your text formatting is a bit odd, don't you think?

> 
> Reported-by: Zheng Wang <hackerzheng666@gmail.com> Zhuorao Yang <alex000young@gmail.com>

Why twice?

Should be two different reported-by lines, right?

Otherwise looks good, can you fix that up and resend?

thanks,

greg k-h