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Date: Wed, 25 Oct 2023 19:41:03 +0200
From: Jann Horn <jannh@...gle.com>
To: "Serge E. Hallyn" <serge@...lyn.com>
Cc: Stefan Bavendiek <stefan.bavendiek@...lbox.org>, kernel-hardening@...ts.openwall.com, 
	linux-hardening@...r.kernel.org
Subject: Re: Isolating abstract sockets

On Wed, Oct 25, 2023 at 7:22 PM Serge E. Hallyn <serge@...lyn.com> wrote:
>
> On Wed, Oct 25, 2023 at 07:10:07PM +0200, Jann Horn wrote:
> > On Tue, Oct 24, 2023 at 3:46 PM Serge E. Hallyn <serge@...lyn.com> wrote:
> > > Disabling them altogether would break lots of things depending on them,
> > > like X :)  (@/tmp/.X11-unix/X0).
> >
> > FWIW, X can connect over both filesystem-based unix domain sockets and
> > abstract unix domain sockets. When a normal X client tries to connect
> > to the server, it'll try a bunch of stuff, including an abstract unix
> > socket address, a filesystem-based unix socket address, and TCP:
> >
> > $ DISPLAY=:12345 strace -f -e trace=connect xev >/dev/null
> > connect(3, {sa_family=AF_UNIX, sun_path=@"/tmp/.X11-unix/X12345"}, 24)
> > = -1 ECONNREFUSED (Connection refused)
> > connect(3, {sa_family=AF_UNIX, sun_path="/tmp/.X11-unix/X12345"}, 110)
> > = -1 ENOENT (No such file or directory)
> > [...]
> > connect(3, {sa_family=AF_INET, sin_port=htons(18345),
> > sin_addr=inet_addr("127.0.0.1")}, 16) = 0
> > connect(3, {sa_family=AF_INET6, sin6_port=htons(18345),
> > inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=htonl(0),
> > sin6_scope_id=0}, 28) = 0
> > connect(3, {sa_family=AF_INET6, sin6_port=htons(18345),
> > inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=htonl(0),
> > sin6_scope_id=0}, 28) = -1 ECONNREFUSED (Connection refused)
> > connect(3, {sa_family=AF_INET, sin_port=htons(18345),
> > sin_addr=inet_addr("127.0.0.1")}, 16) = -1 ECONNREFUSED (Connection
> > refused)
> >
> > And the X server normally listens on both an abstract and a
> > filesystem-based unix socket address (see "netstat --unix -lnp").
> >
> > So rejecting abstract unix socket connections shouldn't prevent an X
> > client from connecting to the X server, I think.
>
> Well it was just an example :)  Dbus is another.  But maybe all
> the users of abstract unix sockets will fall back gracefully to
> something else.  That'd be nice.

For what it's worth, when I try to connect to the session or system
bus on my system (like "strace -f -e trace=connect dbus-send
--session/--system /foo foo"), the connections seem to go directly to
a filesystem socket...

> For X, abstract really doesn't even make sense to me.  Has it always
> supported that?

No idea.

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