From: Kees Cook <keescook@chromium.org>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Sargun Dhillon <sargun@sargun.me>,
Giuseppe Scrivano <gscrivan@redhat.com>,
Robert Sesek <rsesek@google.com>,
Chris Palmer <palmer@google.com>, Jann Horn <jannh@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
containers@lists.linux-foundation.org,
Daniel Wagner <daniel.wagner@bmw-carit.de>,
linux-kernel@vger.kernel.org, Matt Denton <mpdenton@google.com>,
John Fastabend <john.r.fastabend@intel.com>,
linux-fsdevel@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
cgroups@vger.kernel.org, Tejun Heo <tj@kernel.org>,
stable@vger.kernel.org, "David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes
Date: Tue, 9 Jun 2020 13:55:42 -0700 [thread overview]
Message-ID: <202006091346.66B79E07@keescook> (raw)
In-Reply-To: <20200609200346.3fthqgfyw3bxat6l@wittgenstein>
On Tue, Jun 09, 2020 at 10:03:46PM +0200, Christian Brauner wrote:
> I'm looking at __scm_install_fd() and I wonder what specifically you
> mean by that? The put_user() seems to be placed such that the install
> occurrs only if it succeeded. Sure, it only handles a single fd but
> whatever. Userspace knows that already. Just look at systemd when a msg
> fails:
>
> void cmsg_close_all(struct msghdr *mh) {
> struct cmsghdr *cmsg;
>
> assert(mh);
>
> CMSG_FOREACH(cmsg, mh)
> if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS)
> close_many((int*) CMSG_DATA(cmsg), (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int));
> }
>
> The only reasonable scenario for this whole mess I can think of is sm like (pseudo code):
>
> fd_install_received(int fd, struct file *file)
> {
> sock = sock_from_file(fd, &err);
> if (sock) {
> sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> sock_update_classid(&sock->sk->sk_cgrp_data);
> }
>
> fd_install();
> }
>
> error = 0;
> fdarray = malloc(fdmax);
> for (i = 0; i < fdmax; i++) {
> fdarray[i] = get_unused_fd_flags(o_flags);
> if (fdarray[i] < 0) {
> error = -EBADF;
> break;
> }
>
> error = security_file_receive(file);
> if (error)
> break;
>
> error = put_user(fd_array[i], ufd);
> if (error)
> break;
> }
>
> for (i = 0; i < fdmax; i++) {
> if (error) {
> /* ignore errors */
> put_user(-EBADF, ufd); /* If this put_user() fails and the first one succeeded userspace might now close an fd it didn't intend to. */
> put_unused_fd(fdarray[i]);
> } else {
> fd_install_received(fdarray[i], file);
> }
> }
I see 4 cases of the same code pattern (get_unused_fd_flags(),
sock_update_*(), fd_install()), one of them has this difficult put_user()
in the middle, and one of them has a potential replace_fd() instead of
the get_used/fd_install. So, to me, it makes sense to have a helper that
encapsulates the common work that each of those call sites has to do,
which I keep cringing at all these suggestions that leave portions of it
outside the helper.
If it's too ugly to keep the put_user() in the helper, then we can try
what was suggested earlier, and just totally rework the failure path for
SCM_RIGHTS.
LOL. And while we were debating this, hch just went and cleaned stuff
up:
2618d530dd8b ("net/scm: cleanup scm_detach_fds")
So, um, yeah, now my proposal is actually even closer to what we already
have there. We just add the replace_fd() logic to __scm_install_fd() and
we're done with it.
--
Kees Cook
next prev parent reply other threads:[~2020-06-09 20:55 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200603011044.7972-1-sargun@sargun.me>
2020-06-03 1:10 ` [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes Sargun Dhillon
2020-06-04 1:24 ` Christian Brauner
2020-06-04 2:22 ` Kees Cook
2020-06-04 5:20 ` Sargun Dhillon
2020-06-04 12:52 ` Christian Brauner
2020-06-04 13:28 ` David Laight
2020-06-05 7:54 ` Sargun Dhillon
2020-06-09 19:43 ` Kees Cook
2020-06-09 20:03 ` Christian Brauner
2020-06-09 20:55 ` Kees Cook [this message]
2020-06-09 21:27 ` Christian Brauner
2020-06-10 5:27 ` Kees Cook
2020-06-10 8:12 ` Sargun Dhillon
2020-06-10 8:48 ` David Laight
2020-06-11 3:02 ` Kees Cook
2020-06-11 7:51 ` David Laight
2020-06-10 17:10 ` Kees Cook
2020-06-11 2:59 ` Kees Cook
2020-06-11 4:41 ` Sargun Dhillon
2020-06-11 9:19 ` Christian Brauner
2020-06-11 10:39 ` Sargun Dhillon
2020-06-11 23:23 ` Kees Cook
2020-06-11 10:01 ` Christian Brauner
2020-06-11 11:06 ` Sargun Dhillon
2020-06-11 14:42 ` Christian Brauner
2020-06-11 14:56 ` David Laight
2020-06-11 23:49 ` Kees Cook
2020-06-12 6:58 ` Kees Cook
2020-06-12 8:36 ` David Laight
2020-06-12 10:46 ` Sargun Dhillon
2020-06-12 15:13 ` Kees Cook
2020-06-12 15:55 ` David Laight
2020-06-12 18:28 ` Christian Brauner
2020-06-12 18:38 ` Kees Cook
2020-06-12 18:42 ` Christian Brauner
2020-06-15 8:27 ` David Laight
2020-06-10 9:30 ` Christian Brauner
2020-06-04 3:39 ` Sargun Dhillon
2020-06-03 1:10 ` [PATCH v3 2/4] pid: Use file_receive helper to copy FDs Sargun Dhillon
2020-06-03 1:10 ` [PATCH v3 3/4] seccomp: Introduce addfd ioctl to seccomp user notifier Sargun Dhillon
2020-06-03 1:10 ` [PATCH v3 4/4] selftests/seccomp: Test SECCOMP_IOCTL_NOTIF_ADDFD Sargun Dhillon
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