From: Jann Horn <jannh@google.com>
To: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
Eric Biederman <ebiederm@xmission.com>,
Jorge Merlino <jorge.merlino@canonical.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
John Johansen <john.johansen@canonical.com>,
Paul Moore <paul@paul-moore.com>,
James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
Eric Paris <eparis@parisplace.org>,
Richard Haines <richard_c_haines@btinternet.com>,
Casey Schaufler <casey@schaufler-ca.com>,
Xin Long <lucien.xin@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Todd Kjos <tkjos@google.com>,
Ondrej Mosnacek <omosnace@redhat.com>,
Prashanth Prahlad <pprahlad@redhat.com>,
Micah Morton <mortonm@chromium.org>,
Fenghua Yu <fenghua.yu@intel.com>,
Andrei Vagin <avagin@gmail.com>,
linux-kernel@vger.kernel.org, apparmor@lists.ubuntu.com,
linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH 1/2] fs/exec: Explicitly unshare fs_struct on exec
Date: Thu, 6 Oct 2022 16:13:37 +0200 [thread overview]
Message-ID: <CAG48ez0sEkmaez9tYqgMXrkREmXZgxC9fdQD3mzF9cGo_=Tfyg@mail.gmail.com> (raw)
In-Reply-To: <20221006090506.paqjf537cox7lqrq@wittgenstein>
On Thu, Oct 6, 2022 at 11:05 AM Christian Brauner <brauner@kernel.org> wrote:
> On Thu, Oct 06, 2022 at 01:27:34AM -0700, Kees Cook wrote:
> > The check_unsafe_exec() counting of n_fs would not add up under a heavily
> > threaded process trying to perform a suid exec, causing the suid portion
> > to fail. This counting error appears to be unneeded, but to catch any
> > possible conditions, explicitly unshare fs_struct on exec, if it ends up
>
> Isn't this a potential uapi break? Afaict, before this change a call to
> clone{3}(CLONE_FS) followed by an exec in the child would have the
> parent and child share fs information. So if the child e.g., changes the
> working directory post exec it would also affect the parent. But after
> this change here this would no longer be true. So a child changing a
> workding directoro would not affect the parent anymore. IOW, an exec is
> accompanied by an unshare(CLONE_FS). Might still be worth trying ofc but
> it seems like a non-trivial uapi change but there might be few users
> that do clone{3}(CLONE_FS) followed by an exec.
I believe the following code in Chromium explicitly relies on this
behavior, but I'm not sure whether this code is in active use anymore:
https://source.chromium.org/chromium/chromium/src/+/main:sandbox/linux/suid/sandbox.c;l=101?q=CLONE_FS&sq=&ss=chromium
next prev parent reply other threads:[~2022-10-06 14:14 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-06 8:27 [PATCH 0/2] " Kees Cook
2022-10-06 8:27 ` [PATCH 1/2] " Kees Cook
2022-10-06 9:05 ` Christian Brauner
2022-10-06 10:48 ` David Laight
2022-10-06 14:13 ` Jann Horn [this message]
2022-10-06 15:25 ` Kees Cook
2022-10-06 15:35 ` Jann Horn
2025-05-13 13:05 ` Mateusz Guzik
2025-05-13 15:29 ` Eric W. Biederman
2025-05-13 20:57 ` Kees Cook
2025-05-13 21:09 ` Jann Horn
2025-05-13 22:16 ` Eric W. Biederman
2025-05-14 0:03 ` Mateusz Guzik
2025-05-14 15:33 ` Eric W. Biederman
2025-05-14 15:42 ` Kees Cook
2025-05-15 16:48 ` Eric W. Biederman
2025-05-13 23:15 ` Kees Cook
2022-10-14 3:18 ` Andy Lutomirski
2022-10-14 3:54 ` Kees Cook
2022-10-14 15:35 ` Jann Horn
2022-10-18 7:09 ` Kees Cook
2022-10-18 11:19 ` Jann Horn
2022-10-14 22:03 ` David Laight
2022-11-28 17:49 ` Eric W. Biederman
2022-10-06 8:27 ` [PATCH 2/2] exec: Remove LSM_UNSAFE_SHARE Kees Cook
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