bug#47420: binutils is vulnerable to CVE-2021-20197 (and various others)

[Maxime Devos]

On Fri, 2021-03-26 at 21:41 +0100, Léo Le Bouter via Bug reports for GNU Guix 
wrote:
> CVE-2021-20197        18:15
> There is an open race window when writing output in the following
> utilities in GNU binutils version 2.35 and earlier:ar, objcopy, strip,
> ranlib. When these utilities are run as a privileged user (presumably
> as part of a script updating binaries across different users), an
> unprivileged user can trick these utilities into getting ownership of
> arbitrary files through a symlink.

At first I thought -- why would anyone run the binutils as root (or other
privileged user)?  Isn't it only used for *compiling* stuff?  But then
I looked at the actual bug report:

  https://sourceware.org/bugzilla/show_bug.cgi?id=26945

Apparently creating temporary files isn't done quite correctly.
IIUC, on a shared guix system, a malicious user could use this bug
to change the binary that would normally result from the innocent
user running "./configure && make" into something controlled
by the malicious user.

Question: if I run "guix environment guix", do I get the packages
normally used for building guix as-is, or the grafted versions?
When I run "guix environment emacs", I see two lines "applying $N grafts",
so I assume the latter.

> For the two versions packaged in GNU Guix we have:
> 
> $ ./pre-inst-env guix lint -c cve binutils@2.33
> gnu/packages/base.scm:584:2: binutils@2.33.1: probably vulnerable to
> CVE-2020-35493, CVE-2020-35494, CVE-2020-35495, CVE-2020-35496, CVE-
> 2020-35507
> 
> $ ./pre-inst-env guix lint -c cve binutils@2.34
> gnu/packages/base.scm:571:2: binutils@2.34: probably vulnerable to CVE-
> 2020-16590, CVE-2020-16591, CVE-2020-16592, CVE-2020-16593, CVE-2020-
> 16599

> Because they are also build tools for GNU Guix itself, we can't fix
> this in grafts,

No, see next comment.

>  a review of each and every CVE can be made to evaluate
> whether we must fix it for GNU Guix's internal usage can be made, but
> also we should update it and not use any vulnerable version anywhere so
> we can be certain we didnt miss anything.

Guix itself only use binutils in the build containers, which (I presume)
have their own temporary directories, so this shouldn't be
relevant to Guix itself.  However, grafts are still important for
*developers*.  See my first comment block.

> Can binutils be upgraded just like that? Or must it be upgraded in
> tandem with GCC and friends?

I don't know, I guess you'll just have to try and read the release notes.
In any case, upgrading packages seems a good idea (as long as it doesn't
cause world-rebuild or bootstrapping issues of course), even if there
weren't any security issues -- perhaps something to do on core-updates?.

Thanks for looking into these potential security issues,

Greetings,
Maxime.

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