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=80559
Reviewed-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=80919
Reviewed-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=82820
Reviewed-by: Alban Crequy <alban.crequy@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=83772
Reviewed-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>
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=80163
Reviewed-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=80469
Reviewed-by: Alban Crequy <alban.crequy@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=78979
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Colin Walters <walters@verbum.org>
The timeline of events in dbus-launch's main process goes something like this:
* do initial X calls
[1]
* do some other stuff
* fork
(child process starts doing some other stuff)
* return "intermediate parent" pid from fork()
* obtain bus daemon pid from bus_pid_to_launcher_pipe
[2]
* do things that might include X11 calls or killing the dbus-daemon
Meanwhile, the "babysitter" child goes like this:
* return 0 from fork()
[3]
* obtain bus daemon pid from parent process via bus_pid_to_babysitter_pipe
[4]
* do things that might include X11 calls or killing the bus daemon
Before [1] or [3], the right thing to do about an X error is to just
exit. The current implementation called kill(-1) first, which is
undesirable: it kills unrelated processes. With this change, we
just exit.
After [2] or [4], the right thing to do is to kill the dbus-daemon,
and that's what the existing code did.
Between [1] and [2], or between [3] and [4], there is no correct thing
that we can do immediately: we would have to wait for the end of the
"critical section", *then* kill the dbus-daemon. This has not yet been
implemented, so this patch relies for its correctness on the fact that
there are no libX11 calls between those points, so we cannot receive
an X error between them.
dbus-launch deserves more comments, or a reimplementation that is easier to
understand, but this change is certainly better than nothing.
[Commit message added, summarizing reviewers' comments -smcv]
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=74698
Reviewed-by: Simon McVittie
Reviewed-by: Thiago Macieira
It's least confusing if the two files have the same contents. systemd
already knows how to pick up our /var/lib/dbus/machine-id if it exists
and /etc/machine-id doesn't, but the converse is not currently true.
We should make it true, so that it doesn't matter what order
systemd-machine-id-setup and "dbus-uuidgen --ensure" were
invoked in.
In Debian, systemd currently Recommends dbus, so "dbus-uuidgen --ensure"
will *usually* - but not always! - run first, and the two files will
match. However, if you install systemd without dbus, and then install
dbus later, there will be a mismatch. With this change, it doesn't
matter which one is installed first: whichever one happens to come
first, it will generate the machine ID, and then the other one will
copy it.
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77941
Reviewed-by: Lennart Poettering
[Add its source file to SOURCES: this test was previously relying on the
Automake feature that the default value of foo_bar_SOURCES is foo-bar.c. -smcv]
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=73495
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
The algorithm to collapse a subsidiary config file's data into the
master data structure forgot to examine this flag.
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=73475
Reviewed-by: Chengwei Yang <chengwei.yang@intel.com>
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
