[RFC v3 16/22] bpf/cgroup,landlock: Handle Landlock hooks per cgroup

From: MickaÃl SalaÃn
Date: Wed Sep 14 2016 - 03:27:34 EST

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This allows to add new eBPF programs to Landlock hooks dedicated to a
cgroup thanks to the BPF_PROG_ATTACH command. Like for socket eBPF
programs, the Landlock hooks attached to a cgroup are propagated to the
nested cgroups. However, when a new Landlock program is attached to one
of this nested cgroup, this cgroup hierarchy fork the Landlock hooks.
This design is simple and match the current CONFIG_BPF_CGROUP
inheritance. The difference lie in the fact that Landlock programs can
only be stacked but not removed. This match the append-only seccomp
behavior. Userland is free to handle Landlock hooks attached to a cgroup
in more complicated ways (e.g. continuous inheritance), but care should
be taken to properly handle error cases (e.g. memory allocation errors).

Changes since v2:
* new design based on BPF_PROG_ATTACH (suggested by Alexei Starovoitov)

Signed-off-by: MickaÃl SalaÃn <mic@xxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Daniel Mack <daniel@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20160826021432.GA8291@xxxxxxxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20160827204307.GA43714@xxxxxxxxxxxxxxxxxxxxxxx
---
include/linux/bpf-cgroup.h | 7 +++++++
include/linux/cgroup-defs.h | 2 ++
include/linux/landlock.h | 9 +++++++++
include/uapi/linux/bpf.h | 1 +
kernel/bpf/cgroup.c | 33 ++++++++++++++++++++++++++++++---
kernel/bpf/syscall.c | 11 +++++++++++
security/landlock/lsm.c | 40 +++++++++++++++++++++++++++++++++++++++-
security/landlock/manager.c | 32 ++++++++++++++++++++++++++++++++
8 files changed, 131 insertions(+), 4 deletions(-)

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index 6cca7924ee17..439c681159e2 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h
@@ -14,8 +14,15 @@ struct sk_buff;
extern struct static_key_false cgroup_bpf_enabled_key;
#define cgroup_bpf_enabled static_branch_unlikely(&cgroup_bpf_enabled_key)

+#ifdef CONFIG_SECURITY_LANDLOCK
+struct landlock_hooks;
+#endif /* CONFIG_SECURITY_LANDLOCK */
+
union bpf_object {
struct bpf_prog *prog;
+#ifdef CONFIG_SECURITY_LANDLOCK
+ struct landlock_hooks *hooks;
+#endif /* CONFIG_SECURITY_LANDLOCK */
};

struct cgroup_bpf {
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 861b4677fc5b..fe1023bf7b9d 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -301,8 +301,10 @@ struct cgroup {
/* used to schedule release agent */
struct work_struct release_agent_work;

+#ifdef CONFIG_CGROUP_BPF
/* used to store eBPF programs */
struct cgroup_bpf bpf;
+#endif /* CONFIG_CGROUP_BPF */

/* ids of the ancestors at each level including self */
int ancestor_ids[];
diff --git a/include/linux/landlock.h b/include/linux/landlock.h
index 932ae57fa70e..179a848110f3 100644
--- a/include/linux/landlock.h
+++ b/include/linux/landlock.h
@@ -19,6 +19,9 @@
#include <linux/seccomp.h> /* struct seccomp_filter */
#endif /* CONFIG_SECCOMP_FILTER */

+#ifdef CONFIG_CGROUP_BPF
+#include <linux/cgroup-defs.h> /* struct cgroup */
+#endif /* CONFIG_CGROUP_BPF */

#ifdef CONFIG_SECCOMP_FILTER
struct landlock_seccomp_ret {
@@ -65,6 +68,7 @@ struct landlock_hooks {

struct landlock_hooks *new_landlock_hooks(void);
+void get_landlock_hooks(struct landlock_hooks *hooks);
void put_landlock_hooks(struct landlock_hooks *hooks);

#ifdef CONFIG_SECCOMP_FILTER
@@ -73,5 +77,10 @@ int landlock_seccomp_set_hook(unsigned int flags,
const char __user *user_bpf_fd);
#endif /* CONFIG_SECCOMP_FILTER */

+#ifdef CONFIG_CGROUP_BPF
+struct landlock_hooks *landlock_cgroup_set_hook(struct cgroup *cgrp,
+ struct bpf_prog *prog);
+#endif /* CONFIG_CGROUP_BPF */
+
#endif /* CONFIG_SECURITY_LANDLOCK */
#endif /* _LINUX_LANDLOCK_H */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 905dcace7255..12e61508f879 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -124,6 +124,7 @@ enum bpf_prog_type {
enum bpf_attach_type {
BPF_CGROUP_INET_INGRESS,
BPF_CGROUP_INET_EGRESS,
+ BPF_CGROUP_LANDLOCK,
__MAX_BPF_ATTACH_TYPE
};

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 7b75fa692617..1c18fe46958a 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -15,6 +15,7 @@
#include <linux/bpf.h>
#include <linux/bpf-cgroup.h>
#include <net/sock.h>
+#include <linux/landlock.h>

DEFINE_STATIC_KEY_FALSE(cgroup_bpf_enabled_key);
EXPORT_SYMBOL(cgroup_bpf_enabled_key);
@@ -31,7 +32,15 @@ void cgroup_bpf_put(struct cgroup *cgrp)
union bpf_object pinned = cgrp->bpf.pinned[type];

if (pinned.prog) {
- bpf_prog_put(pinned.prog);
+ switch (type) {
+ case BPF_CGROUP_LANDLOCK:
+#ifdef CONFIG_SECURITY_LANDLOCK
+ put_landlock_hooks(pinned.hooks);
+ break;
+#endif /* CONFIG_SECURITY_LANDLOCK */
+ default:
+ bpf_prog_put(pinned.prog);
+ }
static_branch_dec(&cgroup_bpf_enabled_key);
}
}
@@ -53,6 +62,10 @@ void cgroup_bpf_inherit(struct cgroup *cgrp, struct cgroup *parent)
parent->bpf.effective[type].prog,
lockdep_is_held(&cgroup_mutex));
rcu_assign_pointer(cgrp->bpf.effective[type].prog, e.prog);
+#ifdef CONFIG_SECURITY_LANDLOCK
+ if (type == BPF_CGROUP_LANDLOCK)
+ get_landlock_hooks(e.hooks);
+#endif /* CONFIG_SECURITY_LANDLOCK */
}
}

@@ -91,7 +104,18 @@ int __cgroup_bpf_update(struct cgroup *cgrp,
union bpf_object obj, old_pinned, effective;
struct cgroup_subsys_state *pos;

- obj.prog = prog;
+ switch (type) {
+ case BPF_CGROUP_LANDLOCK:
+#ifdef CONFIG_SECURITY_LANDLOCK
+ /* append hook */
+ obj.hooks = landlock_cgroup_set_hook(cgrp, prog);
+ if (IS_ERR(obj.hooks))
+ return PTR_ERR(obj.hooks);
+ break;
+#endif /* CONFIG_SECURITY_LANDLOCK */
+ default:
+ obj.prog = prog;
+ }
old_pinned = xchg(cgrp->bpf.pinned + type, obj);

effective.prog = (!obj.prog && parent) ?
@@ -114,7 +138,10 @@ int __cgroup_bpf_update(struct cgroup *cgrp,
static_branch_inc(&cgroup_bpf_enabled_key);

if (old_pinned.prog) {
- bpf_prog_put(old_pinned.prog);
+#ifdef CONFIG_SECURITY_LANDLOCK
+ if (type != BPF_CGROUP_LANDLOCK)
+ bpf_prog_put(old_pinned.prog);
+#endif /* CONFIG_SECURITY_LANDLOCK */
static_branch_dec(&cgroup_bpf_enabled_key);
}
return 0;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8599596fd6cf..e9c5add327e6 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -846,6 +846,16 @@ static int bpf_prog_attach(const union bpf_attr *attr)
BPF_PROG_TYPE_CGROUP_SOCKET);
break;

+ case BPF_CGROUP_LANDLOCK:
+#ifdef CONFIG_SECURITY_LANDLOCK
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ prog = bpf_prog_get_type(attr->attach_bpf_fd,
+ BPF_PROG_TYPE_LANDLOCK);
+ break;
+#endif /* CONFIG_SECURITY_LANDLOCK */
+
default:
return -EINVAL;
}
@@ -889,6 +899,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
cgroup_put(cgrp);
break;

+ case BPF_CGROUP_LANDLOCK:
default:
return -EINVAL;
}
diff --git a/security/landlock/lsm.c b/security/landlock/lsm.c
index b6e0bace683d..000dd0c7ec3d 100644
--- a/security/landlock/lsm.c
+++ b/security/landlock/lsm.c
@@ -9,6 +9,7 @@
*/

#include <asm/current.h>
+#include <linux/bpf-cgroup.h> /* cgroup_bpf_enabled */
#include <linux/bpf.h> /* enum bpf_reg_type, struct landlock_data */
#include <linux/cred.h>
#include <linux/err.h> /* MAX_ERRNO */
@@ -19,6 +20,10 @@
#include <linux/seccomp.h> /* struct seccomp_* */
#include <linux/types.h> /* uintptr_t */

+#ifdef CONFIG_CGROUP_BPF
+#include <linux/cgroup-defs.h> /* struct cgroup */
+#endif /* CONFIG_CGROUP_BPF */
+
#include "checker_fs.h"
#include "common.h"

@@ -99,6 +104,9 @@ static int landlock_run_prog(enum landlock_hook_id hook_id, __u64 args[6])
#ifdef CONFIG_SECCOMP_FILTER
struct landlock_seccomp_ret *lr;
#endif /* CONFIG_SECCOMP_FILTER */
+#ifdef CONFIG_CGROUP_BPF
+ struct cgroup *cgrp;
+#endif /* CONFIG_CGROUP_BPF */
struct landlock_rule *rule;
u32 hook_idx = get_index(hook_id);

@@ -115,6 +123,11 @@ static int landlock_run_prog(enum landlock_hook_id hook_id, __u64 args[6])

/* TODO: use lockless_dereference()? */

+ /*
+ * Run the seccomp-based triggers before the cgroup-based triggers to
+ * prioritize fine-grained policies (i.e. per thread), and return early.
+ */
+
#ifdef CONFIG_SECCOMP_FILTER
/* seccomp triggers and landlock_ret cleanup */
ctx.origin = LANDLOCK_FLAG_ORIGIN_SECCOMP;
@@ -155,8 +168,21 @@ static int landlock_run_prog(enum landlock_hook_id hook_id, __u64 args[6])
ctx.origin = LANDLOCK_FLAG_ORIGIN_SYSCALL;
ret = landlock_run_prog_for_syscall(hook_idx, &ctx,
current->seccomp.landlock_hooks);
+ if (ret)
+ return -ret;
#endif /* CONFIG_SECCOMP_FILTER */

+#ifdef CONFIG_CGROUP_BPF
+ /* syscall trigger */
+ if (cgroup_bpf_enabled) {
+ ctx.origin = LANDLOCK_FLAG_ORIGIN_SYSCALL;
+ /* get the default cgroup associated with the current thread */
+ cgrp = task_css_set(current)->dfl_cgrp;
+ ret = landlock_run_prog_for_syscall(hook_idx, &ctx,
+ cgrp->bpf.effective[BPF_CGROUP_LANDLOCK].hooks);
+ }
+#endif /* CONFIG_CGROUP_BPF */
+
return -ret;
}

@@ -242,9 +268,21 @@ static struct security_hook_list landlock_hooks[] = {
LANDLOCK_HOOK_INIT(mmap_file),
};

+#ifdef CONFIG_SECCOMP_FILTER
+#ifdef CONFIG_CGROUP_BPF
+#define LANDLOCK_MANAGERS "seccomp and cgroups"
+#else /* CONFIG_CGROUP_BPF */
+#define LANDLOCK_MANAGERS "seccomp"
+#endif /* CONFIG_CGROUP_BPF */
+#elif define(CONFIG_CGROUP_BPF)
+#define LANDLOCK_MANAGERS "cgroups"
+#else
+#error "Need CONFIG_SECCOMP_FILTER or CONFIG_CGROUP_BPF"
+#endif /* CONFIG_SECCOMP_FILTER */
+
void __init landlock_add_hooks(void)
{
- pr_info("landlock: Becoming ready to sandbox with seccomp\n");
+ pr_info("landlock: Becoming ready to sandbox with " LANDLOCK_MANAGERS "\n");
security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks));
}

diff --git a/security/landlock/manager.c b/security/landlock/manager.c
index e9f3f1092023..50aa1305d0d1 100644
--- a/security/landlock/manager.c
+++ b/security/landlock/manager.c
@@ -24,6 +24,11 @@
#include <linux/seccomp.h> /* struct seccomp_filter */
#endif /* CONFIG_SECCOMP_FILTER */

+#ifdef CONFIG_CGROUP_BPF
+#include <linux/bpf-cgroup.h> /* struct cgroup_bpf */
+#include <linux/cgroup-defs.h> /* struct cgroup */
+#endif /* CONFIG_CGROUP_BPF */
+
#include "common.h"

static void put_landlock_rule(struct landlock_rule *rule)
@@ -84,6 +89,12 @@ struct landlock_hooks *new_landlock_hooks(void)
return ret;
}

+inline void get_landlock_hooks(struct landlock_hooks *hooks)
+{
+ if (hooks)
+ atomic_inc(&hooks->usage);
+}
+
/* Limit Landlock hooks to 256KB. */
#define LANDLOCK_HOOKS_MAX_PAGES (1 << 6)

@@ -240,3 +251,24 @@ int landlock_seccomp_set_hook(unsigned int flags, const char __user *user_bpf_fd
return 0;
}
#endif /* CONFIG_SECCOMP_FILTER */
+
+/**
+ * landlock_cgroup_set_hook - attach a Landlock program to a cgroup
+ *
+ * Must be called with cgroup_mutex held.
+ *
+ * @crgp: non-NULL cgroup pointer to attach to
+ * @prog: Landlock program pointer
+ */
+#ifdef CONFIG_CGROUP_BPF
+struct landlock_hooks *landlock_cgroup_set_hook(struct cgroup *cgrp,
+ struct bpf_prog *prog)
+{
+ if (!prog)
+ return ERR_PTR(-EINVAL);
+
+ /* copy the inherited hooks and append a new one */
+ return landlock_set_hook(cgrp->bpf.effective[BPF_CGROUP_LANDLOCK].hooks,
+ prog, NULL);
+}
+#endif /* CONFIG_CGROUP_BPF */
--
2.9.3

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