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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: Wed, 08 Apr 2020 14:09:27 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D25620

--- Comment #16 from Wilco <wdijkstr at arm dot com> ---
(In reply to Szabolcs Nagy from comment #15)
> note that memmove calls memcpy with overlapping
> src and dst (if dst < src).
>=20
> and on an aarch64 kernel a 32bit arm executable with
> mmap(0, -1U/2 + 4097, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
> can succeed.
>=20
> so the bug can be triggered by code using mmap and memmove correctly.
>=20
> however i think relying on memcpy crashing on an overflowed
> size to mitigate bugs in user code is a weak protection.
> (and in general we should not guarantee that memcpy accesses
> all pages in the specified range: there may be a memcpy
> syscall in the future for large copies with whatever semantics
> in case of ub)

Still we should have a new test that checks every string function which has=
 a
size_t input, using a positive test if the huge mmap succeeds and a negative
test checking for a crash. That should flush out any other cases across all
targets.

--=20
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