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From: "wdijkstr at arm dot com" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug libc/25620] Signed comparison vulnerability in the ARMv7
 memcpy() (CVE-2020-6096)
Date: Tue, 07 Apr 2020 17:47:40 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D25620

Wilco <wdijkstr at arm dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |wdijkstr at arm dot com

--- Comment #10 from Wilco <wdijkstr at arm dot com> ---
(In reply to Carlos O'Donell from comment #9)
> (In reply to Richard Earnshaw from comment #8)
> > memcpy is only defined if the regions do not overlap.   If the size of =
the
> > copy is more than half the address space, this can never be true, so any
> > copy that is mis-interpreted as a negative value must be undefined anyw=
ay.
>=20
> In many cases the implementation chooses what behaviour happens in the
> undefined case, and it is always better if we crash early rather than to
> continue to operate having copied less data than expected by the API. If =
we
> change the implementation to operate on unsigned values we will eventually
> reach an unmapped page (likely) and crash. Crashing is the best outcome in
> this case since it prevents the attack from continuing.

Yes it's better to crash, but I fail to see how it would be a security issu=
e.
Assuming we agree values over 2GB are not used in legal programs, then it c=
ould
only happen if the size gets corrupted by a buffer overflow. If that's the
case, an attacker could set it to whatever value they wanted anyway rather =
than
relying on this bug.

--=20
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