On Wed, Dec 11, 2024 at 06:24:53PM +0300, Mikhail Ivanov wrote: > On 12/10/2024 9:05 PM, Mickaël Salaün wrote: > > On Tue, Dec 10, 2024 at 07:04:15PM +0100, Mickaël Salaün wrote: > > > On Mon, Dec 09, 2024 at 01:19:19PM +0300, Mikhail Ivanov wrote: > > > > On 12/4/2024 10:35 PM, Mickaël Salaün wrote: > > > > > On Wed, Dec 04, 2024 at 08:27:58PM +0100, Mickaël Salaün wrote: > > > > > > On Fri, Oct 18, 2024 at 08:08:12PM +0200, Mickaël Salaün wrote: > > > > > > > On Thu, Oct 17, 2024 at 02:59:48PM +0200, Matthieu Baerts wrote: > > > > > > > > Hi Mikhail and Landlock maintainers, > > > > > > > > > > > > > > > > +cc MPTCP list. > > > > > > > > > > > > > > Thanks, we should include this list in the next series. > > > > > > > > > > > > > > > > > > > > > > > On 17/10/2024 13:04, Mikhail Ivanov wrote: > > > > > > > > > Do not check TCP access right if socket protocol is not IPPROTO_TCP. > > > > > > > > > LANDLOCK_ACCESS_NET_BIND_TCP and LANDLOCK_ACCESS_NET_CONNECT_TCP > > > > > > > > > should not restrict bind(2) and connect(2) for non-TCP protocols > > > > > > > > > (SCTP, MPTCP, SMC). > > > > > > > > > > > > > > > > Thank you for the patch! > > > > > > > > > > > > > > > > I'm part of the MPTCP team, and I'm wondering if MPTCP should not be > > > > > > > > treated like TCP here. MPTCP is an extension to TCP: on the wire, we can > > > > > > > > see TCP packets with extra TCP options. On Linux, there is indeed a > > > > > > > > dedicated MPTCP socket (IPPROTO_MPTCP), but that's just internal, > > > > > > > > because we needed such dedicated socket to talk to the userspace. > > > > > > > > > > > > > > > > I don't know Landlock well, but I think it is important to know that an > > > > > > > > MPTCP socket can be used to discuss with "plain" TCP packets: the kernel > > > > > > > > will do a fallback to "plain" TCP if MPTCP is not supported by the other > > > > > > > > peer or by a middlebox. It means that with this patch, if TCP is blocked > > > > > > > > by Landlock, someone can simply force an application to create an MPTCP > > > > > > > > socket -- e.g. via LD_PRELOAD -- and bypass the restrictions. It will > > > > > > > > certainly work, even when connecting to a peer not supporting MPTCP. > > > > > > > > > > > > > > > > Please note that I'm not against this modification -- especially here > > > > > > > > when we remove restrictions around MPTCP sockets :) -- I'm just saying > > > > > > > > it might be less confusing for users if MPTCP is considered as being > > > > > > > > part of TCP. A bit similar to what someone would do with a firewall: if > > > > > > > > TCP is blocked, MPTCP is blocked as well. > > > > > > > > > > > > > > Good point! I don't know well MPTCP but I think you're right. Given > > > > > > > it's close relationship with TCP and the fallback mechanism, it would > > > > > > > make sense for users to not make a difference and it would avoid bypass > > > > > > > of misleading restrictions. Moreover the Landlock rules are simple and > > > > > > > only control TCP ports, not peer addresses, which seems to be the main > > > > > > > evolution of MPTCP. > > > > > > > > > > > > Thinking more about this, this makes sense from the point of view of the > > > > > > network stack, but looking at external (potentially bogus) firewalls or > > > > > > malware detection systems, it is something different. If we don't > > > > > > provide a way for users to differenciate the control of SCTP from TCP, > > > > > > malicious use of SCTP could still bypass this kind of bogus security > > > > > > appliances. It would then be safer to stick to the protocol semantic by > > > > > > clearly differenciating TCP from MPTCP (or any other protocol). > > > > > > > > You mean that these firewals have protocol granularity (e.g. different > > > > restrictions for MPTCP and TCP sockets)? > > > > > > Yes, and more importantly they can miss the MTCP semantic and then not > > > properly filter such packet, which can be use to escape the network > > > policy. See some issues here: > > > https://en.wikipedia.org/wiki/Multipath_TCP > > > > > > The point is that we cannot assume anything about other networking > > > stacks, and if Landlock can properly differentiate between TCP and MTCP > > > (e.g. with new LANDLOCK_ACCESS_NET_CONNECT_MTCP) users of such firewalls > > > could still limit the impact of their firewall's bugs. However, if > > > Landlock treats TCP and MTCP the same way, we'll not be able to only > > > deny MTCP. In most use cases, the network policy should treat both TCP > > > and MTCP the same way though, but we should let users decide according > > > to their context. > > > > > > From an implementation point of view, adding MTCP support should be > > > simple, mainly tests will grow. > > > > s/MTCP/MPTCP/g of course. > > That's reasonable, thanks for explanation! > > We should also consider control of other protocols that use TCP > internally [1], since it should be easy to bypass TCP restriction by > using them (e.g. provoking a fallback of MPTCP or SMC connection to > TCP). > > The simplest solution is to implement separate access rights for SMC and > RDS, as well as for MPTCP. I think we should stick to it. > > I was worried if there was a case where it would be useful to allow only > SMC (and deny TCP). If there are any, it would be more correct to > restrict only the fallback SMC -> TCP with TCP access rights. But such > logic seems too complicated for the kernel and implicit for SMC > applications that can rely on a TCP connection. > > [1] https://lore.kernel.org/all/62336067-18c2-3493-d0ec-6dd6a6d3a1b5@xxxxxxxxxxxxxxxxxxx/ Let's continue the discussion on this thread. > > > > > > > > > > > > > > > > > > > > > > Mikhail, could you please send a new patch series containing one patch > > > > > > to fix the kernel and another to extend tests? > > > > > > > > > > No need to squash them in one, please keep the current split of the test > > > > > patches. However, it would be good to be able to easily backport them, > > > > > or at least the most relevant for this fix, which means to avoid > > > > > extended refactoring. > > > > > > > > No problem, I'll remove the fix of error consistency from this patchset. > > > > BTW, what do you think about second and third commits? Should I send the > > > > new version of them as well (in separate patch)? > > > > > > According to the description, patch 2 may be included in this series if > > > it can be tested with any other LSM, but I cannot read these patches: > > > https://lore.kernel.org/all/20241017110454.265818-3-ivanov.mikhail1@xxxxxxxxxxxxxxxxxxx/ > > Ok I'll do this, since this patch doesn't make any functional changes. > > About readability, a lot of code blocks were moved in this patch, and > because of this, the regular diff file has become too unreadable. > So, I decided to re-generate it with --break-rewrites option of git > format- patch. Do you have any advice on how best to compose a diff for > this patch? The changes are not clear to me so I don't know. If a lot of parts are changed, maybe splitting this patch into a few patches would help. I'm a bit worried that too much parts are changed though. When I try to apply this series I get: Patch failed at 0002 landlock: Make network stack layer checks explicit for each TCP action error: patch failed: security/landlock/net.c:1 error: security/landlock/net.c: patch does not apply
