[bpf-next,03/29] bpf: introduce BPF token object

Add new kind of BPF kernel object, BPF token. BPF token is meant to
allow delegating privileged BPF functionality, like loading a BPF
program or creating a BPF map, from privileged process to a *trusted*
unprivileged process, all while having a good amount of control over which
privileged operations could be performed using provided BPF token.

This is achieved through mounting BPF FS instance with extra delegation
mount options, which determine what operations are delegatable, and also
constraining it to the owning user namespace (as mentioned in the
previous patch).

BPF token itself is just a derivative from BPF FS and can be created
through a new bpf() syscall command, BPF_TOKEN_CREATE, which accepts BPF
FS FD, which can be attained through open() API by opening BPF FS mount
point. Currently, BPF token "inherits" delegated command, map types,
prog type, and attach type bit sets from BPF FS as is. In the future,
having an BPF token as a separate object with its own FD, we can allow
to further restrict BPF token's allowable set of things either at the
creation time or after the fact, allowing the process to guard itself
further from unintentionally trying to load undesired kind of BPF
programs. But for now we keep things simple and just copy bit sets as is.

When BPF token is created from BPF FS mount, we take reference to the
BPF super block's owning user namespace, and then use that namespace for
checking all the {CAP_BPF, CAP_PERFMON, CAP_NET_ADMIN, CAP_SYS_ADMIN}
capabilities that are normally only checked against init userns (using
capable()), but now we check them using ns_capable() instead (if BPF
token is provided). See bpf_token_capable() for details.

Such setup means that BPF token in itself is not sufficient to grant BPF
functionality. User namespaced process has to *also* have necessary
combination of capabilities inside that user namespace. So while
previously CAP_BPF was useless when granted within user namespace, now
it gains a meaning and allows container managers and sys admins to have
a flexible control over which processes can and need to use BPF
functionality within the user namespace (i.e., container in practice).
And BPF FS delegation mount options and derived BPF tokens serve as
a per-container "flag" to grant overall ability to use bpf() (plus further
restrict on which parts of bpf() syscalls are treated as namespaced).

Note also, BPF_TOKEN_CREATE command itself requires ns_capable(CAP_BPF)
within the BPF FS owning user namespace, rounding up the ns_capable()
story of BPF token.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 include/linux/bpf.h            |  41 +++++++
 include/uapi/linux/bpf.h       |  37 ++++++
 kernel/bpf/Makefile            |   2 +-
 kernel/bpf/inode.c             |  12 +-
 kernel/bpf/syscall.c           |  17 +++
 kernel/bpf/token.c             | 214 +++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  37 ++++++
 7 files changed, 354 insertions(+), 6 deletions(-)
 create mode 100644 kernel/bpf/token.c

Message ID	20240103222034.2582628-4-andrii@kernel.org (mailing list archive)
State	Changes Requested
Delegated to:	Paul Moore
Headers	show Received: from mx0a-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D2041F952 for <linux-security-module@vger.kernel.org>; Wed, 3 Jan 2024 22:21:02 +0000 (UTC) From: Andrii Nakryiko <andrii@kernel.org> To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>, <paul@paul-moore.com>, <brauner@kernel.org>, <torvalds@linuxfoundation.org> CC: <linux-fsdevel@vger.kernel.org>, <linux-security-module@vger.kernel.org>, <kernel-team@meta.com> Subject: [PATCH bpf-next 03/29] bpf: introduce BPF token object Date: Wed, 3 Jan 2024 14:20:08 -0800 Message-ID: <20240103222034.2582628-4-andrii@kernel.org> In-Reply-To: <20240103222034.2582628-1-andrii@kernel.org> References: <20240103222034.2582628-1-andrii@kernel.org> Precedence: bulk MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain
Series	BPF token \| expand [bpf-next,00/29] BPF token [bpf-next,01/29] bpf: align CAP_NET_ADMIN checks with bpf_capable() approach [bpf-next,02/29] bpf: add BPF token delegation mount options to BPF FS [bpf-next,03/29] bpf: introduce BPF token object [bpf-next,04/29] bpf: add BPF token support to BPF_MAP_CREATE command [bpf-next,05/29] bpf: add BPF token support to BPF_BTF_LOAD command [bpf-next,06/29] bpf: add BPF token support to BPF_PROG_LOAD command [bpf-next,07/29] bpf: take into account BPF token when fetching helper protos [bpf-next,08/29] bpf: consistently use BPF token throughout BPF verifier logic [bpf-next,09/29] bpf,lsm: refactor bpf_prog_alloc/bpf_prog_free LSM hooks [bpf-next,10/29] bpf,lsm: refactor bpf_map_alloc/bpf_map_free LSM hooks [bpf-next,11/29] bpf,lsm: add BPF token LSM hooks [bpf-next,12/29] libbpf: add bpf_token_create() API [bpf-next,13/29] libbpf: add BPF token support to bpf_map_create() API [bpf-next,14/29] libbpf: add BPF token support to bpf_btf_load() API [bpf-next,15/29] libbpf: add BPF token support to bpf_prog_load() API [bpf-next,16/29] selftests/bpf: add BPF token-enabled tests [bpf-next,17/29] bpf,selinux: allocate bpf_security_struct per BPF token [bpf-next,18/29] bpf: fail BPF_TOKEN_CREATE if no delegation option was set on BPF FS [bpf-next,19/29] bpf: support symbolic BPF FS delegation mount options [bpf-next,20/29] selftests/bpf: utilize string values for delegate_xxx mount options [bpf-next,21/29] libbpf: split feature detectors definitions from cached results [bpf-next,22/29] libbpf: further decouple feature checking logic from bpf_object [bpf-next,23/29] libbpf: move feature detection code into its own file [bpf-next,24/29] libbpf: wire up token_fd into feature probing logic [bpf-next,25/29] libbpf: wire up BPF token support at BPF object level [bpf-next,26/29] selftests/bpf: add BPF object loading tests with explicit token passing [bpf-next,27/29] selftests/bpf: add tests for BPF object load with implicit token [bpf-next,28/29] libbpf: support BPF token path setting through LIBBPF_BPF_TOKEN_PATH envvar [bpf-next,29/29] selftests/bpf: add tests for LIBBPF_BPF_TOKEN_PATH envvar

[bpf-next,03/29] bpf: introduce BPF token object

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