From: Kees Cook <keescook@chromium.org>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Sargun Dhillon <sargun@sargun.me>,
linux-kernel@vger.kernel.org, Tycho Andersen <tycho@tycho.ws>,
Matt Denton <mpdenton@google.com>, Jann Horn <jannh@google.com>,
Chris Palmer <palmer@google.com>,
Aleksa Sarai <cyphar@cyphar.com>,
Robert Sesek <rsesek@google.com>,
containers@lists.linux-foundation.org,
Giuseppe Scrivano <gscrivan@redhat.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Daniel Wagner <daniel.wagner@bmw-carit.de>,
"David S . Miller" <davem@davemloft.net>,
John Fastabend <john.r.fastabend@intel.com>,
Tejun Heo <tj@kernel.org>,
stable@vger.kernel.org, cgroups@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes
Date: Wed, 3 Jun 2020 19:22:57 -0700 [thread overview]
Message-ID: <202006031845.F587F85A@keescook> (raw)
In-Reply-To: <20200604012452.vh33nufblowuxfed@wittgenstein>
On Thu, Jun 04, 2020 at 03:24:52AM +0200, Christian Brauner wrote:
> On Tue, Jun 02, 2020 at 06:10:41PM -0700, Sargun Dhillon wrote:
> > Previously there were two chunks of code where the logic to receive file
> > descriptors was duplicated in net. The compat version of copying
> > file descriptors via SCM_RIGHTS did not have logic to update cgroups.
> > Logic to change the cgroup data was added in:
> > commit 48a87cc26c13 ("net: netprio: fd passed in SCM_RIGHTS datagram not set correctly")
> > commit d84295067fc7 ("net: net_cls: fd passed in SCM_RIGHTS datagram not set correctly")
> >
> > This was not copied to the compat path. This commit fixes that, and thus
> > should be cherry-picked into stable.
> >
> > This introduces a helper (file_receive) which encapsulates the logic for
> > handling calling security hooks as well as manipulating cgroup information.
> > This helper can then be used other places in the kernel where file
> > descriptors are copied between processes
> >
> > I tested cgroup classid setting on both the compat (x32) path, and the
> > native path to ensure that when moving the file descriptor the classid
> > is set.
> >
> > Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> > Suggested-by: Kees Cook <keescook@chromium.org>
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Cc: Christian Brauner <christian.brauner@ubuntu.com>
> > Cc: Daniel Wagner <daniel.wagner@bmw-carit.de>
> > Cc: David S. Miller <davem@davemloft.net>
> > Cc: Jann Horn <jannh@google.com>,
> > Cc: John Fastabend <john.r.fastabend@intel.com>
> > Cc: Tejun Heo <tj@kernel.org>
> > Cc: Tycho Andersen <tycho@tycho.ws>
> > Cc: stable@vger.kernel.org
> > Cc: cgroups@vger.kernel.org
> > Cc: linux-fsdevel@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> > fs/file.c | 35 +++++++++++++++++++++++++++++++++++
> > include/linux/file.h | 1 +
> > net/compat.c | 10 +++++-----
> > net/core/scm.c | 14 ++++----------
> > 4 files changed, 45 insertions(+), 15 deletions(-)
> >
> > diff --git a/fs/file.c b/fs/file.c
> > index abb8b7081d7a..5afd76fca8c2 100644
> > --- a/fs/file.c
> > +++ b/fs/file.c
> > @@ -18,6 +18,9 @@
> > #include <linux/bitops.h>
> > #include <linux/spinlock.h>
> > #include <linux/rcupdate.h>
> > +#include <net/sock.h>
> > +#include <net/netprio_cgroup.h>
> > +#include <net/cls_cgroup.h>
> >
> > unsigned int sysctl_nr_open __read_mostly = 1024*1024;
> > unsigned int sysctl_nr_open_min = BITS_PER_LONG;
> > @@ -931,6 +934,38 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
> > return err;
> > }
> >
> > +/*
> > + * File Receive - Receive a file from another process
> > + *
> > + * This function is designed to receive files from other tasks. It encapsulates
> > + * logic around security and cgroups. The file descriptor provided must be a
> > + * freshly allocated (unused) file descriptor.
> > + *
> > + * This helper does not consume a reference to the file, so the caller must put
> > + * their reference.
> > + *
> > + * Returns 0 upon success.
> > + */
> > +int file_receive(int fd, struct file *file)
>
> This is all just a remote version of fd_install(), yet it deviates from
> fd_install()'s semantics and naming. That's not great imho. What about
> naming this something like:
>
> fd_install_received()
>
> and move the get_file() out of there so it has the same semantics as
> fd_install(). It seems rather dangerous to have a function like
> fd_install() that consumes a reference once it returned and another
> version of this that is basically the same thing but doesn't consume a
> reference because it takes its own. Seems an invitation for confusion.
> Does that make sense?
We have some competing opinions on this, I guess. What I really don't
like is the copy/pasting of the get_unused_fd_flags() and
put_unused_fd() needed by (nearly) all the callers. If it's a helper, it
should help. Specifically, I'd like to see this:
int file_receive(int fd, unsigned long flags, struct file *file,
int __user *fdptr)
{
struct socket *sock;
int err;
err = security_file_receive(file);
if (err)
return err;
if (fd < 0) {
/* Install new fd. */
int new_fd;
err = get_unused_fd_flags(flags);
if (err < 0)
return err;
new_fd = err;
/* Copy fd to any waiting user memory. */
if (fdptr) {
err = put_user(new_fd, fdptr);
if (err < 0) {
put_unused_fd(new_fd);
return err;
}
}
fd_install(new_fd, get_file(file));
fd = new_fd;
} else {
/* Replace existing fd. */
err = replace_fd(fd, file, flags);
if (err)
return err;
}
/* Bump the cgroup usage counts. */
sock = sock_from_file(fd, &err);
if (sock) {
sock_update_netprioidx(&sock->sk->sk_cgrp_data);
sock_update_classid(&sock->sk->sk_cgrp_data);
}
return fd;
}
If everyone else *really* prefers keeping the get_unused_fd_flags() /
put_unused_fd() stuff outside the helper, then I guess I'll give up,
but I think it is MUCH cleaner this way -- all 4 users trim down lots
of code duplication.
--
Kees Cook
next prev parent reply other threads:[~2020-06-04 2:23 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 [this message]
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
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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