Messages in this thread | | | Date | Fri, 8 Jul 2022 09:01:32 -0500 | Subject | Re: [PATCH v2 0/4] Introduce security_create_user_ns() | From | Frederick Lawler <> |
| |
On 7/8/22 7:10 AM, Christian Göttsche wrote: > ,On Fri, 8 Jul 2022 at 00:32, Frederick Lawler <fred@cloudflare.com> wrote: >> >> While creating a LSM BPF MAC policy to block user namespace creation, we >> used the LSM cred_prepare hook because that is the closest hook to prevent >> a call to create_user_ns(). >> >> The calls look something like this: >> >> cred = prepare_creds() >> security_prepare_creds() >> call_int_hook(cred_prepare, ... >> if (cred) >> create_user_ns(cred) >> >> We noticed that error codes were not propagated from this hook and >> introduced a patch [1] to propagate those errors. >> >> The discussion notes that security_prepare_creds() >> is not appropriate for MAC policies, and instead the hook is >> meant for LSM authors to prepare credentials for mutation. [2] >> >> Ultimately, we concluded that a better course of action is to introduce >> a new security hook for LSM authors. [3] >> >> This patch set first introduces a new security_create_user_ns() function >> and create_user_ns LSM hook, then marks the hook as sleepable in BPF. > > Some thoughts: > > I. > > Why not make the hook more generic, e.g. support all other existing > and potential future namespaces?
The main issue with a generic hook is that different namespaces have different calling contexts. We decided in a previous discussion to opt-out of a generic hook for this reason. [1]
> Also I think the naming scheme is <object>_<verb>.
That's a good call out. I was originally hoping to keep the security_*() match with the hook name matched with the caller function to keep things all aligned. If no one objects to renaming the hook, I can rename the hook for v3.
> > LSM_HOOK(int, 0, namespace_create, const struct cred *cred, > unsigned int flags) > > where flags is a bitmap of CLONE flags from include/uapi/linux/sched.h > (like CLONE_NEWUSER). > > II. > > While adding policing for namespaces maybe also add a new hook for setns(2) > > LSM_HOOK(int, 0, namespace_join, const struct cred *subj, const > struct cred *obj, unsigned int flags) >
IIUC, setns() will create a new namespace for the other namespaces except for user namespace. If we add a security hook for the other create_*_ns() functions, then we can catch setns() at that point.
> III. > > Maybe even attach a security context to namespaces so they can be > further governed? > SELinux example: > > type domainA_userns_t; > type_transition domainA_t domainA_t : namespace domainA_userns_t "user"; > allow domainA_t domainA_userns_t:namespace create; > > # domainB calling setns(2) with domainA as target > allow domainB_t domainA_userns_t:namespace join; >
Links: 1. https://lore.kernel.org/all/CAHC9VhSTkEMT90Tk+=iTyp3npWEm+3imrkFVX2qb=XsOPp9F=A@mail.gmail.com/
>> >> Links: >> 1. https://lore.kernel.org/all/20220608150942.776446-1-fred@cloudflare.com/ >> 2. https://lore.kernel.org/all/87y1xzyhub.fsf@email.froward.int.ebiederm.org/ >> 3. https://lore.kernel.org/all/9fe9cd9f-1ded-a179-8ded-5fde8960a586@cloudflare.com/ >> >> Changes since v1: >> - Add selftests/bpf: Add tests verifying bpf lsm create_user_ns hook patch >> - Add selinux: Implement create_user_ns hook patch >> - Change function signature of security_create_user_ns() to only take >> struct cred >> - Move security_create_user_ns() call after id mapping check in >> create_user_ns() >> - Update documentation to reflect changes >> >> Frederick Lawler (4): >> security, lsm: Introduce security_create_user_ns() >> bpf-lsm: Make bpf_lsm_create_user_ns() sleepable >> selftests/bpf: Add tests verifying bpf lsm create_user_ns hook >> selinux: Implement create_user_ns hook >> >> include/linux/lsm_hook_defs.h | 1 + >> include/linux/lsm_hooks.h | 4 + >> include/linux/security.h | 6 ++ >> kernel/bpf/bpf_lsm.c | 1 + >> kernel/user_namespace.c | 5 ++ >> security/security.c | 5 ++ >> security/selinux/hooks.c | 9 ++ >> security/selinux/include/classmap.h | 2 + >> .../selftests/bpf/prog_tests/deny_namespace.c | 88 +++++++++++++++++++ >> .../selftests/bpf/progs/test_deny_namespace.c | 39 ++++++++ >> 10 files changed, 160 insertions(+) >> create mode 100644 tools/testing/selftests/bpf/prog_tests/deny_namespace.c >> create mode 100644 tools/testing/selftests/bpf/progs/test_deny_namespace.c >> >> -- >> 2.30.2 >>
| |