Re: [PATCH v3] x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()

[David Hildenbrand]

On 03.04.25 17:14, Dan Carpenter wrote:
> Sorry, I've been having trouble with my email recently...  I replied
> earlier but my email got eaten on the way out.
>
> What happened here is that the zero day bot emails go to me first and
> then I review them or forward them depending on if they're a real
> issue or not.
>
> Here it's a false postive because it's set and used if the
> (src_vma->vm_flags & VM_PFNMAP) flag is set.  Smatch doesn't parse
> this correctly.  I've been meaning to fix this in Smatch for a
> while.

There is a slight complication (on top of the VM_PFNMAP checks):

If "src_vma->vm_flags & VM_PAT" we
* set pfn
* set dst_vma->vm_flags |= VM_PFNMAP

Then, we only consume the pfn if "dst_vma->vm_flags & VM_PFNMAP"

While we won't be using the uninitialized pfn (good), we'd still pass an 
uninitialized pfn, which IIRC is UB; likely nothing happens on GCC 
clang, but we better handle it.

So that should better be changed; I'll send a fix.

Thanks!

--
Cheers,

David / dhildenb