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Subject[PATCH net-next v7 03/10] bpf,landlock: Define an eBPF program type for a Landlock rule
Date
Add a new type of eBPF program used by Landlock rules.

This new BPF program type will be registered with the Landlock LSM
initialization.

Add an initial Landlock Kconfig.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: James Morris <james.l.morris@oracle.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
---

Changes since v6:
* add 3 more sub-events: IOCTL, LOCK, FCNTL
https://lkml.kernel.org/r/2fbc99a6-f190-f335-bd14-04bdeed35571@digikod.net
* rename LANDLOCK_VERSION to LANDLOCK_ABI to better reflect its purpose,
and move it from landlock.h to common.h
* rename BPF_PROG_TYPE_LANDLOCK to BPF_PROG_TYPE_LANDLOCK_RULE: an eBPF
program could be used for something else than a rule
* simplify struct landlock_context by removing the arch and syscall_nr fields
* remove all eBPF map functions call, remove ABILITY_WRITE
* refactor bpf_landlock_func_proto() (suggested by Kees Cook)
* constify pointers
* fix doc inclusion

Changes since v5:
* rename file hooks.c to init.c
* fix spelling

Changes since v4:
* merge a minimal (not enabled) LSM code and Kconfig in this commit

Changes since v3:
* split commit
* revamp the landlock_context:
* add arch, syscall_nr and syscall_cmd (ioctl, fcntl…) to be able to
cross-check action with the event type
* replace args array with dedicated fields to ease the addition of new
fields
---
include/linux/bpf_types.h | 3 ++
include/uapi/linux/bpf.h | 97 +++++++++++++++++++++++++++++++++++++++++
security/Kconfig | 1 +
security/Makefile | 2 +
security/landlock/Kconfig | 18 ++++++++
security/landlock/Makefile | 3 ++
security/landlock/common.h | 21 +++++++++
security/landlock/init.c | 98 ++++++++++++++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 97 +++++++++++++++++++++++++++++++++++++++++
9 files changed, 340 insertions(+)
create mode 100644 security/landlock/Kconfig
create mode 100644 security/landlock/Makefile
create mode 100644 security/landlock/common.h
create mode 100644 security/landlock/init.c

diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
index 6f1a567667b8..8bac93970a47 100644
--- a/include/linux/bpf_types.h
+++ b/include/linux/bpf_types.h
@@ -18,6 +18,9 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_KPROBE, kprobe_prog_ops)
BPF_PROG_TYPE(BPF_PROG_TYPE_TRACEPOINT, tracepoint_prog_ops)
BPF_PROG_TYPE(BPF_PROG_TYPE_PERF_EVENT, perf_event_prog_ops)
#endif
+#ifdef CONFIG_SECURITY_LANDLOCK
+BPF_PROG_TYPE(BPF_PROG_TYPE_LANDLOCK_RULE, bpf_landlock_ops)
+#endif

BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8541ab85e432..20da634da941 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -129,6 +129,7 @@ enum bpf_prog_type {
BPF_PROG_TYPE_LWT_XMIT,
BPF_PROG_TYPE_SOCK_OPS,
BPF_PROG_TYPE_SK_SKB,
+ BPF_PROG_TYPE_LANDLOCK_RULE,
};

enum bpf_attach_type {
@@ -879,4 +880,100 @@ enum {
#define TCP_BPF_IW 1001 /* Set TCP initial congestion window */
#define TCP_BPF_SNDCWND_CLAMP 1002 /* Set sndcwnd_clamp */

+/**
+ * enum landlock_subtype_event - event occurring when an action is performed on
+ * a particular kernel object
+ *
+ * An event is a policy decision point which exposes the same context type
+ * (especially the same arg[0-9] field types) for each rule execution.
+ *
+ * @LANDLOCK_SUBTYPE_EVENT_UNSPEC: invalid value
+ * @LANDLOCK_SUBTYPE_EVENT_FS: generic filesystem event
+ * @LANDLOCK_SUBTYPE_EVENT_FS_IOCTL: custom IOCTL sub-event
+ * @LANDLOCK_SUBTYPE_EVENT_FS_LOCK: custom LOCK sub-event
+ * @LANDLOCK_SUBTYPE_EVENT_FS_FCNTL: custom FCNTL sub-event
+ */
+enum landlock_subtype_event {
+ LANDLOCK_SUBTYPE_EVENT_UNSPEC,
+ LANDLOCK_SUBTYPE_EVENT_FS,
+ LANDLOCK_SUBTYPE_EVENT_FS_IOCTL,
+ LANDLOCK_SUBTYPE_EVENT_FS_LOCK,
+ LANDLOCK_SUBTYPE_EVENT_FS_FCNTL,
+};
+#define _LANDLOCK_SUBTYPE_EVENT_LAST LANDLOCK_SUBTYPE_EVENT_FS_FCNTL
+
+/**
+ * DOC: landlock_subtype_ability
+ *
+ * eBPF context and functions allowed for a rule
+ *
+ * - LANDLOCK_SUBTYPE_ABILITY_DEBUG: allows to do debug actions (e.g. writing
+ * logs), which may be dangerous and should only be used for rule testing
+ */
+#define LANDLOCK_SUBTYPE_ABILITY_DEBUG (1ULL << 0)
+#define _LANDLOCK_SUBTYPE_ABILITY_NB 1
+#define _LANDLOCK_SUBTYPE_ABILITY_MASK ((1ULL << _LANDLOCK_SUBTYPE_ABILITY_NB) - 1)
+
+/*
+ * Future options for a Landlock rule (e.g. run even if a previous rule denied
+ * an action).
+ */
+#define _LANDLOCK_SUBTYPE_OPTION_NB 0
+#define _LANDLOCK_SUBTYPE_OPTION_MASK ((1ULL << _LANDLOCK_SUBTYPE_OPTION_NB) - 1)
+
+/*
+ * Status visible in the @status field of a context (e.g. already called in
+ * this syscall session, with same args...).
+ *
+ * The @status field exposed to a rule shall depend on the rule version.
+ */
+#define _LANDLOCK_SUBTYPE_STATUS_NB 0
+#define _LANDLOCK_SUBTYPE_STATUS_MASK ((1ULL << _LANDLOCK_SUBTYPE_STATUS_NB) - 1)
+
+/**
+ * DOC: landlock_action_fs
+ *
+ * - %LANDLOCK_ACTION_FS_EXEC: execute a file or walk through a directory
+ * - %LANDLOCK_ACTION_FS_WRITE: modify a file or a directory view (which
+ * include mount actions)
+ * - %LANDLOCK_ACTION_FS_READ: read a file or a directory
+ * - %LANDLOCK_ACTION_FS_NEW: create a file or a directory
+ * - %LANDLOCK_ACTION_FS_GET: open or receive a file
+ * - %LANDLOCK_ACTION_FS_REMOVE: unlink a file or remove a directory
+ *
+ * Each of the following actions are specific to syscall multiplexers. Each of
+ * them trigger a dedicated Landlock event where their command can be read.
+ *
+ * - %LANDLOCK_ACTION_FS_IOCTL: ioctl command
+ * - %LANDLOCK_ACTION_FS_LOCK: flock or fcntl lock command
+ * - %LANDLOCK_ACTION_FS_FCNTL: fcntl command
+ */
+#define LANDLOCK_ACTION_FS_EXEC (1ULL << 0)
+#define LANDLOCK_ACTION_FS_WRITE (1ULL << 1)
+#define LANDLOCK_ACTION_FS_READ (1ULL << 2)
+#define LANDLOCK_ACTION_FS_NEW (1ULL << 3)
+#define LANDLOCK_ACTION_FS_GET (1ULL << 4)
+#define LANDLOCK_ACTION_FS_REMOVE (1ULL << 5)
+#define LANDLOCK_ACTION_FS_IOCTL (1ULL << 6)
+#define LANDLOCK_ACTION_FS_LOCK (1ULL << 7)
+#define LANDLOCK_ACTION_FS_FCNTL (1ULL << 8)
+#define _LANDLOCK_ACTION_FS_NB 9
+#define _LANDLOCK_ACTION_FS_MASK ((1ULL << _LANDLOCK_ACTION_FS_NB) - 1)
+
+
+/**
+ * struct landlock_context - context accessible to a Landlock rule
+ *
+ * @status: bitfield for future use (LANDLOCK_SUBTYPE_STATUS_*)
+ * @event: event type (&enum landlock_subtype_event)
+ * @arg1: event's first optional argument
+ * @arg2: event's second optional argument
+ */
+struct landlock_context {
+ __u64 status;
+ __u64 event;
+ __u64 arg1;
+ __u64 arg2;
+};
+
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/security/Kconfig b/security/Kconfig
index e8e449444e65..2dd023c90bcd 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -211,6 +211,7 @@ source security/tomoyo/Kconfig
source security/apparmor/Kconfig
source security/loadpin/Kconfig
source security/yama/Kconfig
+source security/landlock/Kconfig

source security/integrity/Kconfig

diff --git a/security/Makefile b/security/Makefile
index f2d71cdb8e19..3fdc2f19dc48 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -9,6 +9,7 @@ subdir-$(CONFIG_SECURITY_TOMOYO) += tomoyo
subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor
subdir-$(CONFIG_SECURITY_YAMA) += yama
subdir-$(CONFIG_SECURITY_LOADPIN) += loadpin
+subdir-$(CONFIG_SECURITY_LANDLOCK) += landlock

# always enable default capabilities
obj-y += commoncap.o
@@ -24,6 +25,7 @@ obj-$(CONFIG_SECURITY_TOMOYO) += tomoyo/
obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/
obj-$(CONFIG_SECURITY_YAMA) += yama/
obj-$(CONFIG_SECURITY_LOADPIN) += loadpin/
+obj-$(CONFIG_SECURITY_LANDLOCK) += landlock/
obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o

# Object integrity file lists
diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig
new file mode 100644
index 000000000000..aa5808e116f1
--- /dev/null
+++ b/security/landlock/Kconfig
@@ -0,0 +1,18 @@
+config SECURITY_LANDLOCK
+ bool "Landlock sandbox support"
+ depends on SECURITY
+ depends on BPF_SYSCALL
+ depends on SECCOMP_FILTER
+ default y
+ help
+ Landlock is a stackable LSM which allows to load a security policy to
+ restrict processes (i.e. create a sandbox). The policy is a list of
+ stacked eBPF programs, called rules, dedicated to restrict access to
+ a type of kernel object (e.g. file).
+
+ You need to enable seccomp filter to apply a security policy to a
+ process hierarchy (e.g. application with built-in sandboxing).
+
+ See Documentation/security/landlock/ for further information.
+
+ If you are unsure how to answer this question, answer Y.
diff --git a/security/landlock/Makefile b/security/landlock/Makefile
new file mode 100644
index 000000000000..7205f9a7a2ee
--- /dev/null
+++ b/security/landlock/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
+
+landlock-y := init.o
diff --git a/security/landlock/common.h b/security/landlock/common.h
new file mode 100644
index 000000000000..c82cbd3fb640
--- /dev/null
+++ b/security/landlock/common.h
@@ -0,0 +1,21 @@
+/*
+ * Landlock LSM - private headers
+ *
+ * Copyright © 2016-2017 Mickaël Salaün <mic@digikod.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _SECURITY_LANDLOCK_COMMON_H
+#define _SECURITY_LANDLOCK_COMMON_H
+
+/*
+ * This is not intended for the UAPI headers. Each userland software should use
+ * a static minimal ABI for the required features as explained in the
+ * documentation.
+ */
+#define LANDLOCK_ABI 1
+
+#endif /* _SECURITY_LANDLOCK_COMMON_H */
diff --git a/security/landlock/init.c b/security/landlock/init.c
new file mode 100644
index 000000000000..c7922a91aa57
--- /dev/null
+++ b/security/landlock/init.c
@@ -0,0 +1,98 @@
+/*
+ * Landlock LSM - init
+ *
+ * Copyright © 2016-2017 Mickaël Salaün <mic@digikod.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/bpf.h> /* enum bpf_access_type */
+#include <linux/capability.h> /* capable */
+
+#include "common.h" /* LANDLOCK_* */
+
+
+static inline bool bpf_landlock_is_valid_access(int off, int size,
+ enum bpf_access_type type, struct bpf_insn_access_aux *info,
+ const union bpf_prog_subtype *prog_subtype)
+{
+ if (WARN_ON(!prog_subtype))
+ return false;
+
+ switch (prog_subtype->landlock_rule.event) {
+ case LANDLOCK_SUBTYPE_EVENT_FS:
+ case LANDLOCK_SUBTYPE_EVENT_UNSPEC:
+ default:
+ return false;
+ }
+}
+
+static inline bool bpf_landlock_is_valid_subtype(
+ const union bpf_prog_subtype *prog_subtype)
+{
+ if (WARN_ON(!prog_subtype))
+ return false;
+
+ switch (prog_subtype->landlock_rule.event) {
+ case LANDLOCK_SUBTYPE_EVENT_FS:
+ break;
+ case LANDLOCK_SUBTYPE_EVENT_UNSPEC:
+ default:
+ return false;
+ }
+
+ /* check Landlock ABI compatibility */
+ if (!prog_subtype->landlock_rule.abi ||
+ prog_subtype->landlock_rule.abi > LANDLOCK_ABI)
+ return false;
+ /* check if the rule's event, ability and option make sense */
+ if (!prog_subtype->landlock_rule.event ||
+ prog_subtype->landlock_rule.event >
+ _LANDLOCK_SUBTYPE_EVENT_LAST)
+ return false;
+ if (prog_subtype->landlock_rule.ability &
+ ~_LANDLOCK_SUBTYPE_ABILITY_MASK)
+ return false;
+ if (prog_subtype->landlock_rule.option &
+ ~_LANDLOCK_SUBTYPE_OPTION_MASK)
+ return false;
+
+ /* the ability to debug requires global CAP_SYS_ADMIN */
+ if (prog_subtype->landlock_rule.ability &
+ LANDLOCK_SUBTYPE_ABILITY_DEBUG &&
+ !capable(CAP_SYS_ADMIN))
+ return false;
+
+ return true;
+}
+
+static inline const struct bpf_func_proto *bpf_landlock_func_proto(
+ enum bpf_func_id func_id,
+ const union bpf_prog_subtype *prog_subtype)
+{
+ /* generic functions */
+ if (prog_subtype->landlock_rule.ability &
+ LANDLOCK_SUBTYPE_ABILITY_DEBUG) {
+ switch (func_id) {
+ case BPF_FUNC_get_current_comm:
+ return &bpf_get_current_comm_proto;
+ case BPF_FUNC_get_current_pid_tgid:
+ return &bpf_get_current_pid_tgid_proto;
+ case BPF_FUNC_get_current_uid_gid:
+ return &bpf_get_current_uid_gid_proto;
+ case BPF_FUNC_trace_printk:
+ return bpf_get_trace_printk_proto();
+ default:
+ break;
+ }
+ }
+ return NULL;
+}
+
+const struct bpf_verifier_ops bpf_landlock_ops = {
+ .get_func_proto = bpf_landlock_func_proto,
+ .is_valid_access = bpf_landlock_is_valid_access,
+ .is_valid_subtype = bpf_landlock_is_valid_subtype,
+};
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2c0dc9d58ea0..e83bdecf9d27 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -129,6 +129,7 @@ enum bpf_prog_type {
BPF_PROG_TYPE_LWT_XMIT,
BPF_PROG_TYPE_SOCK_OPS,
BPF_PROG_TYPE_SK_SKB,
+ BPF_PROG_TYPE_LANDLOCK_RULE,
};

enum bpf_attach_type {
@@ -868,4 +869,100 @@ enum {
#define TCP_BPF_IW 1001 /* Set TCP initial congestion window */
#define TCP_BPF_SNDCWND_CLAMP 1002 /* Set sndcwnd_clamp */

+/**
+ * enum landlock_subtype_event - event occurring when an action is performed on
+ * a particular kernel object
+ *
+ * An event is a policy decision point which exposes the same context type
+ * (especially the same arg[0-9] field types) for each rule execution.
+ *
+ * @LANDLOCK_SUBTYPE_EVENT_UNSPEC: invalid value
+ * @LANDLOCK_SUBTYPE_EVENT_FS: generic filesystem event
+ * @LANDLOCK_SUBTYPE_EVENT_FS_IOCTL: custom IOCTL sub-event
+ * @LANDLOCK_SUBTYPE_EVENT_FS_LOCK: custom LOCK sub-event
+ * @LANDLOCK_SUBTYPE_EVENT_FS_FCNTL: custom FCNTL sub-event
+ */
+enum landlock_subtype_event {
+ LANDLOCK_SUBTYPE_EVENT_UNSPEC,
+ LANDLOCK_SUBTYPE_EVENT_FS,
+ LANDLOCK_SUBTYPE_EVENT_FS_IOCTL,
+ LANDLOCK_SUBTYPE_EVENT_FS_LOCK,
+ LANDLOCK_SUBTYPE_EVENT_FS_FCNTL,
+};
+#define _LANDLOCK_SUBTYPE_EVENT_LAST LANDLOCK_SUBTYPE_EVENT_FS_FCNTL
+
+/**
+ * DOC: landlock_subtype_ability
+ *
+ * eBPF context and functions allowed for a rule
+ *
+ * - LANDLOCK_SUBTYPE_ABILITY_DEBUG: allows to do debug actions (e.g. writing
+ * logs), which may be dangerous and should only be used for rule testing
+ */
+#define LANDLOCK_SUBTYPE_ABILITY_DEBUG (1ULL << 0)
+#define _LANDLOCK_SUBTYPE_ABILITY_NB 1
+#define _LANDLOCK_SUBTYPE_ABILITY_MASK ((1ULL << _LANDLOCK_SUBTYPE_ABILITY_NB) - 1)
+
+/*
+ * Future options for a Landlock rule (e.g. run even if a previous rule denied
+ * an action).
+ */
+#define _LANDLOCK_SUBTYPE_OPTION_NB 0
+#define _LANDLOCK_SUBTYPE_OPTION_MASK ((1ULL << _LANDLOCK_SUBTYPE_OPTION_NB) - 1)
+
+/*
+ * Status visible in the @status field of a context (e.g. already called in
+ * this syscall session, with same args...).
+ *
+ * The @status field exposed to a rule shall depend on the rule version.
+ */
+#define _LANDLOCK_SUBTYPE_STATUS_NB 0
+#define _LANDLOCK_SUBTYPE_STATUS_MASK ((1ULL << _LANDLOCK_SUBTYPE_STATUS_NB) - 1)
+
+/**
+ * DOC: landlock_action_fs
+ *
+ * - %LANDLOCK_ACTION_FS_EXEC: execute a file or walk through a directory
+ * - %LANDLOCK_ACTION_FS_WRITE: modify a file or a directory view (which
+ * include mount actions)
+ * - %LANDLOCK_ACTION_FS_READ: read a file or a directory
+ * - %LANDLOCK_ACTION_FS_NEW: create a file or a directory
+ * - %LANDLOCK_ACTION_FS_GET: open or receive a file
+ * - %LANDLOCK_ACTION_FS_REMOVE: unlink a file or remove a directory
+ *
+ * Each of the following actions are specific to syscall multiplexers. Each of
+ * them trigger a dedicated Landlock event where their command can be read.
+ *
+ * - %LANDLOCK_ACTION_FS_IOCTL: ioctl command
+ * - %LANDLOCK_ACTION_FS_LOCK: flock or fcntl lock command
+ * - %LANDLOCK_ACTION_FS_FCNTL: fcntl command
+ */
+#define LANDLOCK_ACTION_FS_EXEC (1ULL << 0)
+#define LANDLOCK_ACTION_FS_WRITE (1ULL << 1)
+#define LANDLOCK_ACTION_FS_READ (1ULL << 2)
+#define LANDLOCK_ACTION_FS_NEW (1ULL << 3)
+#define LANDLOCK_ACTION_FS_GET (1ULL << 4)
+#define LANDLOCK_ACTION_FS_REMOVE (1ULL << 5)
+#define LANDLOCK_ACTION_FS_IOCTL (1ULL << 6)
+#define LANDLOCK_ACTION_FS_LOCK (1ULL << 7)
+#define LANDLOCK_ACTION_FS_FCNTL (1ULL << 8)
+#define _LANDLOCK_ACTION_FS_NB 9
+#define _LANDLOCK_ACTION_FS_MASK ((1ULL << _LANDLOCK_ACTION_FS_NB) - 1)
+
+
+/**
+ * struct landlock_context - context accessible to a Landlock rule
+ *
+ * @status: bitfield for future use (LANDLOCK_SUBTYPE_STATUS_*)
+ * @event: event type (&enum landlock_subtype_event)
+ * @arg1: event's first optional argument
+ * @arg2: event's second optional argument
+ */
+struct landlock_context {
+ __u64 status;
+ __u64 event;
+ __u64 arg1;
+ __u64 arg2;
+};
+
#endif /* _UAPI__LINUX_BPF_H__ */
--
2.14.1
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