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From: "fweimer at redhat 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 18:07:14 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D25620

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com

--- Comment #11 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to Wilco from comment #10)
> Yes it's better to crash, but I fail to see how it would be a security
> issue. Assuming we agree values over 2GB are not used in legal programs,
> then it could 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.

I think the relevant case is when the size is set to -1 (or something else
close to zero) statically due to a size computation that went wrong as the
result of a logic error, and not some arbitrary attacker-controlled value.

Maybe we can change __memcpy_chk to call __chk_fail if the most significant=
 bit
of the dynamic length argument is set, independently of the value of the
destination length? Then at least applications built with -D_FORTIFY_SOURCE
would benefit from that kind of belt-and-suspenders hardening.

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