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This is a symptom of either a denial of service attack, or a
serious performance problem. Either way, sysadmins should know.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=86431

We now have a private mailing list that can be the security contact.

This makes bus_context_check_security_policy follow convention of
setting errors if function indicates failure and has error parameter.
Notable implication is that AccessDenied error will be sent if sending message
to addressed recipient is denied due to receive rule. Previously, message
was silently dropped.

This also fixes assertion failure when message is denied at addressed recipient
while sending pending auto activation messages.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=86194

This ensures that our rlimit is actually high enough to avoid the
denial of service described in CVE-2014-3636 part A.
CVE-2014-7824 has been allocated for this incomplete fix.

Restore the original rlimit for activated services, to avoid
them getting undesired higher limits.

(Thanks to Alban Crequy for various adjustments which have been
included in this commit.)

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=85105Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>

This addresses CVE-2014-3635.

If (*n_fds * sizeof (int) % sizeof (size_t)) is nonzero,
then CMSG_SPACE (*n_fds * sizeof (int)) > CMSG_LEN (*n_fds * sizeof (int)
because the SPACE includes padding to a size_t boundary, whereas the LEN
does not. We have to allocate the SPACE. Previously, we told the kernel
that the buffer size we wanted was the SPACE, not the LEN, which meant
it was free to fill the padding with additional fds: on a 64-bit
platform with 32-bit int, that's one extra fd, if *n_fds happens
to be odd.

This meant that a malicious sender could send exactly 1 fd too many,
which would make us fail an assertion if enabled, or overrun a buffer
by 1 fd otherwise.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=83622Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>

This means we can use _DBUS_STATIC_ASSERT at non-global scope without
tripping -Wunused-local-typedefs.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=83767Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>
(cherry picked from commit 0e3d08d4)

This is one of four commits needed to address CVE-2014-3637.

The bus uses _dbus_connection_set_pending_fds_function and
_dbus_connection_get_pending_fds_count to be notified when there are pending
file descriptors. A timeout per connection is armed and disarmed when the file
descriptor list is used and emptied.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80559Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

This is one of four commits needed to address CVE-2014-3637.

This will allow the bus to be notified whenever a file descriptor is added or
removed from a DBusConnection's DBusMessageLoader.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80559Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

This is one of four commits needed to address CVE-2014-3637.

This will allow the bus to know whether there are pending file descriptors in a
DBusConnection's DBusMessageLoader.

https://bugs.freedesktop.org/show_bug.cgi?id=80559Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
[fix compilation on platforms that do not HAVE_UNIX_FD_PASSING -smcv]
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

This is one of four commits needed to address CVE-2014-3637.

When a file descriptor is passed to dbus-daemon, the associated D-Bus message
might not be fully sent to dbus-daemon yet. Dbus-daemon keeps the file
descriptor in the DBusMessageLoader of the connection, waiting for the rest of
the message. If the client stops sending the remaining bytes, dbus-daemon will
wait forever and keep that file descriptor.

This patch adds pending_fd_timeout (milliseconds) in the configuration to
disconnect a connection after a timeout when a file descriptor was sent but not
the remaining message.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80559Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

This addresses the parts of CVE-2014-3639 not already addressed by
reducing the default authentication timeout.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80851
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80919Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

This partially addresses CVE-2014-3639.

This will change the default on the system bus where the limit
  <limit name="auth_timeout">...</limit>
is not specified.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80919Reviewed-by: Thiago Macieira <thiago@kde.org>
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

This addresses CVE-2014-3636.

Based on a patch by Alban Crequy. Now that it's the same on all
platforms, there's little point in it being set by configure/cmake.

This change fixes two distinct denials of service:

fd.o#82820, part A
------------------

Before this patch, the system bus had the following default configuration:
- max_connections_per_user: 256
- DBUS_DEFAULT_MESSAGE_UNIX_FDS: usually 1024 (or 256 on QNX, see fd.o#61176)
  as defined by configure.ac
- max_incoming_unix_fds: DBUS_DEFAULT_MESSAGE_UNIX_FDS*4 = usually 4096
- max_outgoing_unix_fds: DBUS_DEFAULT_MESSAGE_UNIX_FDS*4 = usually 4096
- max_message_unix_fds: DBUS_DEFAULT_MESSAGE_UNIX_FDS = usually 1024

This means that a single user could create 256 connections and transmit
256*4096 = 1048576 file descriptors.

The file descriptors stay attached to the dbus-daemon process while they are
in the message loader, in the outgoing queue or waiting to be dispatched before
D-Bus activation.

dbus-daemon is usually limited to 65536 file descriptors (ulimit -n). If the
limit is reached and dbus-daemon needs to receive a message with a file
descriptor attached, this is signalled by recvfrom with the flag MSG_CTRUNC.
Dbus-daemon cannot recover from that error because the kernel does not have any
API to retrieve a file descriptor which has been discarded with MSG_CTRUNC.
Therefore, it closes the connection of the sender. This is not necessarily the
connection which generated the most file descriptors so it can lead to
denial-of-service attacks.

In order to prevent DoS issues, this patch reduces DEFAULT_MESSAGE_UNIX_FDS to
16:

max_connections_per_user * max_incoming_unix_fds = 256 * 64 = 16384

This is less than the usual "ulimit -n" (65536) with a good margin to
accomodate the other sources of file descriptors (stdin/stdout/stderr,
listening sockets, message loader, etc.).

Distributors on non-Linux may need to configure a smaller limit in
system.conf, if their limit on the number of fds is smaller than
Linux's.

fd.o#82820, part B
------------------

On Linux, it's not possible to send more than 253 fds in a single sendmsg()
call: sendmsg() would return -EINVAL.
  #define SCM_MAX_FD      253

SCM_MAX_FD changed value during Linux history:
- it used to be (OPEN_MAX-1)
- commit c09edd6eb (Jul 2007) changed it to 255
- commit bba14de98 (Nov 2010) changed it to 253

Libdbus always sends all of a message's fds, and the beginning
of the message itself, in a single sendmsg() call. Combining these
two, a malicious sender could split a message across two or more
sendmsg() calls to construct a composite message with 254 or more
fds. When dbus-daemon attempted to relay that message to its
recipient in a single sendmsg() call, it would receive EINVAL,
interpret that as a fatal socket error and disconnect the recipient,
resulting in denial of service.

This is fixed by keeping max_message_unix_fds <= SCM_MAX_FD.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=82820Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>

This addresses CVE-2014-3638.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=81053Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

Whenever I forget to turn off corekeeper, the regression tests
take ages to record all test-segfault's crashes.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=83772Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>

systemd 209 merged all the libraries to libsystemd. Old
libraries can still be enabled with --enable-compat-libs
switch in systemd but this increases the binary size.

Implement a fallback library check in case compat libraries
dont exist.

[Fixed underquoting; switched priority so we try libsystemd first -smcv]
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=41252Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

Bug-Gentoo: https://bugs.gentoo.org/show_bug.cgi?id=507232
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=81043Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

Since Linux commit 25888e (from 2.6.37-rc4, Nov 2010), sendmsg() on Unix
sockets returns -1 errno=ETOOMANYREFS ("Too many references: cannot splice")
when the passfd mechanism (SCM_RIGHTS) is "abusively" used recursively by
applications. A malicious client could use this to force a victim system
service to be disconnected from the system bus; the victim would likely
respond by exiting. This is a denial of service (fd.o #80163,
CVE-2014-3532).

This patch silently drops the D-Bus message on ETOOMANYREFS and does not close
the connection.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80163Reviewed-by: Thiago Macieira <thiago@kde.org>
[altered commit message to explain DoS significance -smcv]
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

There were two bugs here: we would previously overwrite the unused
fds with the already-used fds instead of the other way round, and
we would copy n bytes where we should have copied n ints.

Additionally, sending crafted messages in a chosen sequence to a victim
system service could cause an invalid file descriptor to be present
when dbus-daemon tries to forward one of those crafted messages to the
victim, causing sendmsg() to fail with EBADF, which resulted in
disconnecting the victim service, which would likely respond to that
by exiting. This is a denial of service (fd.o #80469, CVE-2014-3533).

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=79694
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=80469Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=74698Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

How it should work:

When a D-Bus message activates a service, LSMs (SELinux or AppArmor) check
whether the message can be delivered after the service has been activated. The
service is considered activated when its well-known name is requested with
org.freedesktop.DBus.RequestName. When the message delivery is denied, the
service stays activated but should not receive the activating message (the
message which triggered the activation). dbus-daemon is supposed to drop the
activating message and reply to the sender with a D-Bus error message.

However, it does not work as expected:

1. The error message is delivered to the service instead of being delivered to
   the sender. As an example, the error message could be something like:

     An SELinux policy prevents this sender from sending this
     message to this recipient, [...] member="MaliciousMethod"

   If the sender and the service are malicious confederates and agree on a
   protocol to insert information in the member name, the sender can leak
   information to the service, even though the LSM attempted to block the
   communication between the sender and the service.

2. The error message is delivered as a reply to the RequestName call from
   service. It means the activated service will believe it cannot request the
   name and might exit. The sender could activate the service frequently and
   systemd will give up activating it. Thus the denial of service.

The following changes fix the bug:
- bus_activation_send_pending_auto_activation_messages() only returns an error
  in case of OOM. The prototype is changed to return TRUE, or FALSE on OOM
  (and its only caller sets the OOM error).
- When a client is not allowed to talk to the service, a D-Bus error message
  is pre-allocated to be delivered to the client as part of the transaction.
  The error is not propagated to the caller so RequestName will not fail
  (except on OOM).

[fixed a misleading comment -smcv]

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=78979Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Colin Walters <walters@verbum.org>

On W32 dbus daemon will print output in text mode, with 0x0d0a EOLs instead
of just 0x0a. Be able to handle that.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=75863
Reviewed-by: Simon McVittie