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Message-Id: <20230814-devcg_guard-v1-1-654971ab88b1@aisec.fraunhofer.de>
Date: Mon, 14 Aug 2023 16:26:09 +0200
From: Michael Weiß <michael.weiss@...ec.fraunhofer.de>
To: Alexander Mikhalitsyn <alexander@...alicyn.com>,
Christian Brauner <brauner@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Quentin Monnet <quentin@...valent.com>,
Alexander Viro <viro@...iv.linux.org.uk>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, gyroidos@...ec.fraunhofer.de,
Michael Weiß <michael.weiss@...ec.fraunhofer.de>
Subject: [PATCH RFC 1/4] bpf: add cgroup device guard to flag a cgroup
device prog
Introduce the BPF_F_CGROUP_DEVICE_GUARD flag for BPF_PROG_LOAD
which allows to set a cgroup device program to be a device guard.
Later this may be used to guard actions on device nodes in
non-initial userns. For this reason we provide the helper function
cgroup_bpf_device_guard_enabled() to check if a task has a cgroups
device program which is a device guard in its effective set of bpf
programs.
Signed-off-by: Michael Weiß <michael.weiss@...ec.fraunhofer.de>
---
include/linux/bpf-cgroup.h | 7 +++++++
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 5 +++++
kernel/bpf/cgroup.c | 30 ++++++++++++++++++++++++++++++
kernel/bpf/syscall.c | 5 ++++-
tools/include/uapi/linux/bpf.h | 5 +++++
6 files changed, 52 insertions(+), 1 deletion(-)
diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index 57e9e109257e..112b6093f9fd 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h
@@ -184,6 +184,8 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
return array != &bpf_empty_prog_array.hdr;
}
+bool cgroup_bpf_device_guard_enabled(struct task_struct *task);
+
/* Wrappers for __cgroup_bpf_run_filter_skb() guarded by cgroup_bpf_enabled. */
#define BPF_CGROUP_RUN_PROG_INET_INGRESS(sk, skb) \
({ \
@@ -476,6 +478,11 @@ static inline int bpf_percpu_cgroup_storage_update(struct bpf_map *map,
return 0;
}
+static bool cgroup_bpf_device_guard_enabled(struct task_struct *task)
+{
+ return false;
+}
+
#define cgroup_bpf_enabled(atype) (0)
#define BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, atype, t_ctx) ({ 0; })
#define BPF_CGROUP_RUN_SA_PROG(sk, uaddr, atype) ({ 0; })
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f58895830ada..313cce8aee05 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1384,6 +1384,7 @@ struct bpf_prog_aux {
bool sleepable;
bool tail_call_reachable;
bool xdp_has_frags;
+ bool cgroup_device_guard;
/* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
const struct btf_type *attach_func_proto;
/* function name for valid attach_btf_id */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 60a9d59beeab..3be57f7957b1 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1165,6 +1165,11 @@ enum bpf_link_type {
*/
#define BPF_F_XDP_DEV_BOUND_ONLY (1U << 6)
+/* If BPF_F_CGROUP_DEVICE_GUARD is used in BPF_PROG_LOAD command, the loaded
+ * program will be allowed to guard device access inside user namespaces.
+ */
+#define BPF_F_CGROUP_DEVICE_GUARD (1U << 7)
+
/* link_create.kprobe_multi.flags used in LINK_CREATE command for
* BPF_TRACE_KPROBE_MULTI attach type to create return probe.
*/
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 5b2741aa0d9b..230693ca4cdb 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -2505,6 +2505,36 @@ const struct bpf_verifier_ops cg_sockopt_verifier_ops = {
const struct bpf_prog_ops cg_sockopt_prog_ops = {
};
+bool
+cgroup_bpf_device_guard_enabled(struct task_struct *task)
+{
+ bool ret;
+ const struct bpf_prog_array *array;
+ const struct bpf_prog_array_item *item;
+ const struct bpf_prog *prog;
+ struct cgroup *cgrp = task_dfl_cgroup(task);
+
+ ret = false;
+
+ array = rcu_access_pointer(cgrp->bpf.effective[CGROUP_DEVICE]);
+ if (array == &bpf_empty_prog_array.hdr)
+ return ret;
+
+ mutex_lock(&cgroup_mutex);
+ array = rcu_dereference_protected(cgrp->bpf.effective[CGROUP_DEVICE],
+ lockdep_is_held(&cgroup_mutex));
+ item = &array->items[0];
+ while ((prog = READ_ONCE(item->prog))) {
+ if (prog->aux->cgroup_device_guard) {
+ ret = true;
+ break;
+ }
+ item++;
+ }
+ mutex_unlock(&cgroup_mutex);
+ return ret;
+}
+
/* Common helpers for cgroup hooks. */
const struct bpf_func_proto *
cgroup_common_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a2aef900519c..33ea67c702c1 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2564,7 +2564,8 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
BPF_F_SLEEPABLE |
BPF_F_TEST_RND_HI32 |
BPF_F_XDP_HAS_FRAGS |
- BPF_F_XDP_DEV_BOUND_ONLY))
+ BPF_F_XDP_DEV_BOUND_ONLY |
+ BPF_F_CGROUP_DEVICE_GUARD))
return -EINVAL;
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
@@ -2651,6 +2652,8 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
prog->aux->dev_bound = !!attr->prog_ifindex;
prog->aux->sleepable = attr->prog_flags & BPF_F_SLEEPABLE;
prog->aux->xdp_has_frags = attr->prog_flags & BPF_F_XDP_HAS_FRAGS;
+ prog->aux->cgroup_device_guard =
+ attr->prog_flags & BPF_F_CGROUP_DEVICE_GUARD;
err = security_bpf_prog_alloc(prog->aux);
if (err)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 60a9d59beeab..3be57f7957b1 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1165,6 +1165,11 @@ enum bpf_link_type {
*/
#define BPF_F_XDP_DEV_BOUND_ONLY (1U << 6)
+/* If BPF_F_CGROUP_DEVICE_GUARD is used in BPF_PROG_LOAD command, the loaded
+ * program will be allowed to guard device access inside user namespaces.
+ */
+#define BPF_F_CGROUP_DEVICE_GUARD (1U << 7)
+
/* link_create.kprobe_multi.flags used in LINK_CREATE command for
* BPF_TRACE_KPROBE_MULTI attach type to create return probe.
*/
--
2.30.2
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