Re: CVE-2023-52451: powerpc/pseries/memhp: Fix access beyond end of drmem array

[Michal Hocko]

On Mon 26-02-24 16:06:51, Greg KH wrote:
> On Mon, Feb 26, 2024 at 03:52:11PM +0100, Michal Hocko wrote:
> > On Thu 22-02-24 17:21:58, Greg KH wrote:
> > > Description
> > > ===========
> > > 
> > > In the Linux kernel, the following vulnerability has been resolved:
> > > 
> > > powerpc/pseries/memhp: Fix access beyond end of drmem array
> > > 
> > > dlpar_memory_remove_by_index() may access beyond the bounds of the
> > > drmem lmb array when the LMB lookup fails to match an entry with the
> > > given DRC index. When the search fails, the cursor is left pointing to
> > > &drmem_info->lmbs[drmem_info->n_lmbs], which is one element past the
> > > last valid entry in the array. The debug message at the end of the
> > > function then dereferences this pointer:
> > > 
> > >         pr_debug("Failed to hot-remove memory at %llx\n",
> > >                  lmb->base_addr);
> > 
> > While this is a reasonable fix and the stable material it is really
> > unclear to me why it has gained a CVE. Memory hotplug is a privileged
> > operation. Could you clarify please?
> 
> As you know, history has shown us that accessing out of your allocated
> memory can cause problems, and we can not assume use-cases, as we don't
> know how everyone uses our codebase, so marking places where we fix
> out-of-bound memory accesses is resolving a weakness in the codebase,
> hence a CVE assignment.

Does that mean that any potentially incorrect input provided by an admin is
considered CVE now? I guess we would need to ban interfaces like
/dev/mem and many others.
 
> If your systems are not vulnerable to this specific issue, wonderful, no
> need to take it, but why wouldn't you want to take a fix that resolves a
> known weakness?

I have explicitly said, the fix is reasonable. I just do not see a point
to mark it as CVE. I fail to see any thread model where this would
matter as it would require untrusted privileged actor to trigger it
AFAICS. I am happy to be proven wrong here.

-- 
Michal Hocko
SUSE Labs