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Date: Thu, 18 Nov 2021 16:21:13 -0300
From: √Črico Nogueira <ericonr@...root.org>
To: <musl@...ts.openwall.com>
Cc: <monk@...oiled.info>
Subject: Re: $ORIGIN rpath expansion without /proc: code looks wrong

On Wed Nov 17, 2021 at 5:01 PM -03, Jeffrey Walton wrote:
> On Wed, Nov 17, 2021 at 12:09 PM √Črico Nogueira <ericonr@...root.org>
> wrote:
> >
> > On Wed Nov 17, 2021 at 11:04 AM -03, Alexander Sosedkin wrote:
> > > ...
> > > Could somebody take a look at this and double-check that
> > > this codepath makes sense?
> >
> > It does, but it might not be as robust as you wish. fixup_rpath() treats
> > the RPATH entry as a single string, and does all $ORIGIN substitutions
> > in one go (what splits the string by ":" is open_path()). This means
> > that the entire RPATH entry containing $ORIGIN will be ignored if
> > /proc/self/exe can't be accessed, despite one or more of them not
> > depending on $ORIGIN.
>
> This has come up before on the list. It is different behavior from
> libc, and it may be CVE worthy if a down-level library is used when an
> updated library is available but lost because the RPATH/RUNPATH is
> discarded.

I would file such a CVE on the distro packaging or system administration
rather than musl. The binaries you need to run so /proc is mounted
shouldn't be the sort that depend on dynamic RPATH using ${ORIGIN}
(rather than a static one or no RPATH at all), and any security fix
should be confirmed to actually work before being deployed...

Furthermore, I don't think an unprivileged user should be able to
unmount /proc unless they have called prctl(PR_SET_NO_NEW_PRIVS, 1), no?
Which would make any "attacks" be directed at themselves.

>
> Jeff

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