Re: WARNING: CPU: 1 PID: 52 at mm/page_alloc.c:4826 __alloc_pages_nodemask (Re: [PATCH 5/5] sysctl: pass kernel pointers to ->proc_handler)

[Christoph Hellwig]

On Mon, Jun 08, 2020 at 09:45:49AM +0200, Vegard Nossum wrote:
> Just a test case.
>
> Allowing the kernel to allocate an unbounded amount of memory on behalf
> of userspace is an easy DOS.
>
> All the length checks were already in there, e.g.
>
>  static int cmm_timeout_handler(struct ctl_table *ctl, int write,
>                               void __user *buffer, size_t *lenp, loff_t 
> *ppos)
>  {
>         char buf[64], *p;
> [...]
>                 len = min(*lenp, sizeof(buf));
>                 if (copy_from_user(buf, buffer, len))
>                         return -EFAULT;

Doesn't help if we don't know the exact limit yet.  But we can put
some arbitrary but reasonable limit like KMALLOC_MAX_SIZE on the
sysctls and see if this sticks.