From: Aleksa Sarai <cyphar@cyphar.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
Andrew Lutomirski <luto@kernel.org>, Jann Horn <jannh@google.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Jeff Layton <jlayton@kernel.org>,
"J. Bruce Fields" <bfields@fieldses.org>,
Arnd Bergmann <arnd@arndb.de>,
David Howells <dhowells@redhat.com>,
Eric Biederman <ebiederm@xmission.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alexei Starovoitov <ast@kernel.org>,
Kees Cook <keescook@chromium.org>,
Christian Brauner <christian@brauner.io>,
Tycho Andersen <tycho@tycho.ws>,
David Drysdale <drysdale@google.com>,
Chanho Min <chanho.min@lge.com>, Oleg Nesterov <oleg@redhat.com>,
Aleksa Sarai <asarai@suse.de>,
Linux Containers <containers@lists.linux-foundation.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
kernel list <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH v6 5/6] binfmt_*: scope path resolution of interpreters
Date: Sun, 12 May 2019 23:35:49 +1000 [thread overview]
Message-ID: <20190512133549.ymx5yg5rdqvavzyq@yavin> (raw)
In-Reply-To: <CAHk-=wh3dT7=SMjvSZreXSu36Cg7gsfSipLhfTz5ioDKXV5uHg@mail.gmail.com>
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On 2019-05-12, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Sat, May 11, 2019 at 7:37 PM Andy Lutomirski <luto@amacapital.net> wrote:
> > I bet this will break something that already exists. An execveat()
> > flag to turn off /proc/self/exe would do the trick, though.
>
> Thinking more about it, I suspect it is (once again) wrong to let the
> thing that does the execve() control that bit.
>
> Generally, the less we allow people to affect the lifetime and
> environment of a suid executable, the better off we are.
>
> But maybe we could limit /proc/*/exe to at least not honor suid'ness
> of the target? Or does chrome/runc depend on that too?
Speaking on the runc side, we don't depend on this. It's possible
someone depends on this for fexecve(3) -- but as mentioned before in
newer kernels glibc uses execve(AT_EMPTY_PATH).
I would like to point out though that I'm a little bit cautious about
/proc/self/exe-specific restrictions -- because a trivial way to get
around them would be to just open it with O_PATH (and you end up with a
/proc/self/fd/ which is equivalent). Unfortunately blocking setuid exec
on all O_PATH descriptors would break even execve(AT_EMPTY_PATH) of
setuid descriptors.
The patches I mentioned (which Andy and I discussed off-list) would
effectively make the magiclink modes in /proc/ affect how you can
operate on the path (no write bit in the mode, cannot re-open it write).
One aspect of this is how to handle O_PATH and in particular how do we
handle an O_PATH re-open of an already-restricted magiclink.
Maybe we could make it so that setuid is disallowed if you are dealing
with an O_PATH fd which was a magiclink. Effectively, on O_PATH open you
get an fmode_t saying FMODE_SETUID_EXEC_ALLOWED *but* if the path is a
magiclink this fmode gets dropped and when the fd is given to
execveat(AT_EMPTY_PATH) the fmode is checked and setuid-exec is not
allowed.
[I assume in this discussion "setuid" means "setuid + setcap", right?]
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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next prev parent reply other threads:[~2019-05-12 13:37 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-06 16:54 [PATCH v6 0/6] namei: resolveat(2) path resolution restriction API Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 1/6] namei: split out nd->dfd handling to dirfd_path_init Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 2/6] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 3/6] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 4/6] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 5/6] binfmt_*: scope path resolution of interpreters Aleksa Sarai
2019-05-06 18:37 ` Jann Horn
2019-05-06 19:17 ` Aleksa Sarai
2019-05-06 23:41 ` Andy Lutomirski
2019-05-08 0:54 ` Aleksa Sarai
2019-05-10 20:41 ` Jann Horn
2019-05-10 21:20 ` Andy Lutomirski
2019-05-10 22:55 ` Jann Horn
2019-05-10 23:36 ` Christian Brauner
2019-05-11 15:49 ` Aleksa Sarai
2019-05-11 17:00 ` Andy Lutomirski
2019-05-11 17:21 ` Linus Torvalds
2019-05-11 17:26 ` Linus Torvalds
2019-05-11 17:31 ` Aleksa Sarai
2019-05-11 17:43 ` Linus Torvalds
2019-05-11 17:48 ` Christian Brauner
2019-05-11 18:00 ` Aleksa Sarai
2019-05-11 22:39 ` Andy Lutomirski
[not found] ` <CAHk-=wg3+3GfHsHdB4o78jNiPh_5ShrzxBuTN-Y8EZfiFMhCvw@mail.gmail.com>
2019-05-12 10:19 ` Christian Brauner
[not found] ` <9CD2B97D-A6BD-43BE-9040-B410D996A195@amacapital.net>
2019-05-12 10:44 ` Linus Torvalds
2019-05-12 13:35 ` Aleksa Sarai [this message]
2019-05-12 13:38 ` Aleksa Sarai
2019-05-12 14:34 ` Andy Lutomirski
2019-05-11 17:26 ` Aleksa Sarai
2019-05-08 0:38 ` Eric W. Biederman
2019-05-10 20:10 ` Jann Horn
2019-05-06 16:54 ` [PATCH v6 6/6] namei: resolveat(2) syscall Aleksa Sarai
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