Re: [PATCH v6 1/3] random: add vgetrandom_alloc() syscall

[Arnd Bergmann]

On Thu, Nov 24, 2022, at 13:48, Jason A. Donenfeld wrote:
> On Thu, Nov 24, 2022 at 01:24:42PM +0100, Jason A. Donenfeld wrote:

> Looks like set_mempolicy, get_mempoliy, and migrate_pages pass an
> unsigned long pointer and I don't see any compat stuff around it:
>
>     SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long 
> __user *, nmask,
>                     unsigned long, maxnode)
>    
>     SYSCALL_DEFINE5(get_mempolicy, int __user *, policy,
>                     unsigned long __user *, nmask, unsigned long, maxnode,
>                     unsigned long, addr, unsigned long, flags)
>
>     SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
>                     const unsigned long __user *, old_nodes,
>                     const unsigned long __user *, new_nodes)

Compat handling for these is done all the way down in the
pointer access:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/mempolicy.c#n1368

This works here because it's a special bitmap but is not the
best approach if you just have a pointer to a single value.

       Arnd