On 13/03/2023 18:16, Konstantin Meskhidze (A) wrote:
2/24/2023 1:17 AM, Günther Noack пишет:
Hello Konstantin!
Sorry for asking such fundamental questions again so late in the review.
After playing with patch V9 with the Go-Landlock library, I'm still
having trouble understanding these questions -- they probably have
good answers, but I also did not see them explained in the
documentation. Maybe it would help to clarify it there?
* What is the use case for permitting processes to connect to a given
TCP port, but leaving unspecified what the IP address is?
Example: If a Landlock ruleset permits connecting to TCP port 53,
that makes it possible to talk to any IP address on the internet (at
least if the process runs on a normal Linux desktop machine), and we
can't really control whether that is the system's proper (TCP-)DNS
server or whether that is an attacker-controlled service for
accepting leaked secrets from the process...?
Is the plan that IP address support should be added in a follow-up
patch? Will it become part of the landlock_net_service_attr struct?
In the beginning I introduced the idea with IP address to
Mickaël but he suggested to use port-based granularity. So with ports
it's worth using Landlock in containerized applications working within
one IP address. Anyway it's possible to use netfilter to control
incoming traffic. It's a good question - we should discuss it carefuly.
Limiting access rule definition to TCP ports is because of two reasons:
- practical one: start with something small and improve it. All new
features should be covered by tests, and it takes time to write and
review them, especially to cover IPv4, IPv6 and any other type of
address to identify a server. Being able to control TCP connect and bind
is useful and brings the scaffolding for other non-kernel-object
restrictions.
- semantic one: ports are tied to well-known (or configured) services,
whatever the network where a process is (e.g. Internet, LAN, container's
network namespace, VM). However, IP addresses are not well-known but
(most of the time) tied to names/DNS, which is not handled by the kernel
but user space. Moreover, I think it makes sense for app/service
developers to think about reachable services, but much less about
servers, which depend on the local network and a system-wide configuration.
For some use cases, there is definitely a need to restrict access to a
set of servers though. I think a new dedicated attr struct would be
easier to handle and it would make more sense to compose them (ANDing
all network rule types to make a final decision). This new struct could
define different kind of subnets (IPv4, IPv6, ethernet, bluetooth…). One
of this type could be the local link, and especially if the server is
local to the system or not (i.e. loopback interface), and if the server
is in a specified network namespace (e.g. specific container/pod).
Anyway, this should indeed be documented.
* Given the list of obscure network protocols listed in the socket(2)
man page, I find it slightly weird to have rules for the use of TCP,
but to leave less prominent protocols unrestricted.
For example, a process with an enabled Landlock network ruleset may
connect only to certain TCP ports, but at the same time it can
happily use Bluetooth/CAN bus/DECnet/IPX or other protocols?
We also have started a discussion about UDP protocol, but it's
more complicated since UDP sockets does not establish connections
between each other. There is a performance problem on the first place here.
I'm not familiar with Bluetooth/CAN bus/DECnet/IPX but let's discuss it.
Any ideas here?
All these protocols should be handled one way or another someday. ;)
I'm mentioning these more obscure protocols, because I doubt that
Landlock will grow more sophisticated support for them anytime soon,
so maybe the best option would be to just make it possible to
disable these? Is that also part of the plan?
(I think there would be a lot of value in restricting network
access, even when it's done very broadly. There are many programs
that don't need network at all, and among those that do need
network, most only require IP networking.
Indeed, protocols that nobody care to make Landlock supports them will
probably not have fine-grained control. We could extend the ruleset
attributes to disable the use (i.e. not only the creation of new related
sockets/resources) of network protocol families, in a way that would
make sandboxes simulate a kernel without such protocol support. In this
case, this should be an allowed list of protocols, and everything not in
that list should be denied. This approach could be used for other kernel
features (unrelated to network).
Btw, the argument for more broad disabling of network access was
already made at https://cr.yp.to/unix/disablenetwork.html in the
past.)
This is interesting but scoped to a single use case. As specified at the
beginning of this linked page, there must be exceptions, not only with
AF_UNIX but also for (the newer) AF_VSOCK, and probably future ones.
This is why I don't think a binary approach is a good one for Linux.
Users should be able to specify what they need, and block the rest.
Thanks for the link. I will read it.
* This one is more of an implementation question: I don't understand
why we are storing the networking rules in the same RB tree as the
file system rules. - It looks a bit like "YAGNI" to me...?
Actually network rules are stored in a different RB tree.
You can check it in struct landlock_ruleset (ruleset.h):
- struct rb_root root_inodeis for fs rules
- struct rb_root root_net_port is for network rules;
Would it be more efficient to keep the file system rules in the
existing RB tree, and store the networking rules *separately* next
to it in a different RB tree, or even in a more optimized data
structure? In pseudocode:
struct fast_lookup_int_set bind_tcp_ports;
struct fast_lookup_int_set connect_tcp_ports;
struct landlock_rb_tree fs_rules;
It seems that there should be a data structure that supports this
well and which uses the fact that we only need to store small
integers?
Thnaks for the question. From my point of view it depends on a
real scenario - how many ports we want to allow by Landlock for a
proccess - thousands, hundreds or less. If it's just 10 ports - do we
really need some optimized data structure? Do we get some performance
gain here?
What do you think?
As Konstantin explained, there are two different red-black trees. This
data structure may not be optimal but it is much easier to start with that.
Using one tree per right would increase the size, especially for each
new access right, but it is worth thinking about a new data structure
dealing with sets (and ranges) of numbers.
Talking about performance optimization, the first step would be to use a
hash table for domain's inode identification.
Thanks,
–Günther
P.S.: Apologies if some of it was discussed previously. I did my best
to catch up on previous threads, but it's long, and it's possible that
I missed parts of the discussion.
On Mon, Jan 16, 2023 at 04:58:06PM +0800, Konstantin Meskhidze wrote:
Hi,
This is a new V9 patch related to Landlock LSM network confinement.
It is based on the landlock's -next branch on top of v6.2-rc3 kernel version:
https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git/log/?h=next
It brings refactoring of previous patch version V8.
Mostly there are fixes of logic and typos, adding new tests.
All test were run in QEMU evironment and compiled with
-static flag.
1. network_test: 32/32 tests passed.
2. base_test: 7/7 tests passed.
3. fs_test: 78/78 tests passed.
4. ptrace_test: 8/8 tests passed.
Previous versions:
v8: https://lore.kernel.org/linux-security-module/20221021152644.155136-1-konstantin.meskhidze@xxxxxxxxxx/
v7: https://lore.kernel.org/linux-security-module/20220829170401.834298-1-konstantin.meskhidze@xxxxxxxxxx/
v6: https://lore.kernel.org/linux-security-module/20220621082313.3330667-1-konstantin.meskhidze@xxxxxxxxxx/
v5: https://lore.kernel.org/linux-security-module/20220516152038.39594-1-konstantin.meskhidze@xxxxxxxxxx
v4: https://lore.kernel.org/linux-security-module/20220309134459.6448-1-konstantin.meskhidze@xxxxxxxxxx/
v3: https://lore.kernel.org/linux-security-module/20220124080215.265538-1-konstantin.meskhidze@xxxxxxxxxx/
v2: https://lore.kernel.org/linux-security-module/20211228115212.703084-1-konstantin.meskhidze@xxxxxxxxxx/
v1: https://lore.kernel.org/linux-security-module/20211210072123.386713-1-konstantin.meskhidze@xxxxxxxxxx/
Konstantin Meskhidze (11):
landlock: Make ruleset's access masks more generic
landlock: Refactor landlock_find_rule/insert_rule
landlock: Refactor merge/inherit_ruleset functions
landlock: Move and rename umask_layers() and init_layer_masks()
landlock: Refactor _unmask_layers() and _init_layer_masks()
landlock: Refactor landlock_add_rule() syscall
landlock: Add network rules and TCP hooks support
selftests/landlock: Share enforce_ruleset()
selftests/landlock: Add 10 new test suites dedicated to network
samples/landlock: Add network demo
landlock: Document Landlock's network support
Mickaël Salaün (1):
landlock: Allow filesystem layout changes for domains without such
rule type
Documentation/userspace-api/landlock.rst | 72 +-
include/uapi/linux/landlock.h | 49 +
samples/landlock/sandboxer.c | 131 +-
security/landlock/Kconfig | 1 +
security/landlock/Makefile | 2 +
security/landlock/fs.c | 255 ++--
security/landlock/limits.h | 7 +-
security/landlock/net.c | 200 +++
security/landlock/net.h | 26 +
security/landlock/ruleset.c | 409 +++++--
security/landlock/ruleset.h | 185 ++-
security/landlock/setup.c | 2 +
security/landlock/syscalls.c | 165 ++-
tools/testing/selftests/landlock/base_test.c | 2 +-
tools/testing/selftests/landlock/common.h | 10 +
tools/testing/selftests/landlock/config | 4 +
tools/testing/selftests/landlock/fs_test.c | 75 +-
tools/testing/selftests/landlock/net_test.c | 1157 ++++++++++++++++++
18 files changed, 2398 insertions(+), 354 deletions(-)
create mode 100644 security/landlock/net.c
create mode 100644 security/landlock/net.h
create mode 100644 tools/testing/selftests/landlock/net_test.c
--
2.25.1
.
