Add eBPF functions to compare file system access with a Landlock file
system handle:
* bpf_landlock_cmp_fs_prop_with_struct_file(prop, map, map_op, file)
This function allows to compare the dentry, inode, device or mount
point of the currently accessed file, with a reference handle.
* bpf_landlock_cmp_fs_beneath_with_struct_file(opt, map, map_op, file)
This function allows an eBPF program to check if the current accessed
file is the same or in the hierarchy of a reference handle.
The goal of file system handle is to abstract kernel objects such as a
struct file or a struct inode. Userland can create this kind of handle
thanks to the BPF_MAP_UPDATE_ELEM command. The element is a struct
landlock_handle containing the handle type (e.g.
BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) and a file descriptor. This could
also be any descriptions able to match a struct file or a struct inode
(e.g. path or glob string).
Signed-off-by: Mickaël Salaün <m...@digikod.net>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Alexei Starovoitov <a...@kernel.org>
Cc: James Morris <james.l.mor...@oracle.com>
Cc: Serge E. Hallyn <se...@hallyn.com>
Cc: David S. Miller <da...@davemloft.net>
Cc: Daniel Borkmann <dan...@iogearbox.net>
---
include/linux/bpf.h | 4 +-
include/uapi/linux/bpf.h | 52 +++++++++++-
kernel/bpf/arraymap.c | 17 +++-
kernel/bpf/verifier.c | 6 ++
security/landlock/Makefile | 2 +-
security/landlock/checker_fs.c | 183 +++++++++++++++++++++++++++++++++++++++++
security/landlock/checker_fs.h | 20 +++++
security/landlock/lsm.c | 11 ++-
8 files changed, 288 insertions(+), 7 deletions(-)
create mode 100644 security/landlock/checker_fs.c
create mode 100644 security/landlock/checker_fs.h
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 557e7efdf0cd..79014aedbea4 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -84,6 +84,7 @@ enum bpf_arg_type {
ARG_PTR_TO_STRUCT_FILE, /* pointer to struct file */
ARG_PTR_TO_STRUCT_CRED, /* pointer to struct cred */
+ ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS, /* pointer to Landlock FS
handle */
};
/* type of values returned from helper functions */
@@ -146,6 +147,7 @@ enum bpf_reg_type {
/* Landlock */
PTR_TO_STRUCT_FILE,
PTR_TO_STRUCT_CRED,
+ CONST_PTR_TO_LANDLOCK_HANDLE_FS,
};
struct bpf_prog;
@@ -207,7 +209,7 @@ struct bpf_array {
#ifdef CONFIG_SECURITY_LANDLOCK
struct map_landlock_handle {
- u32 type;
+ u32 type; /* e.g. BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD */
union {
struct file *file;
};
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 983d14e910ff..88af79dd668c 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -89,10 +89,20 @@ enum bpf_map_type {
enum bpf_map_array_type {
BPF_MAP_ARRAY_TYPE_UNSPEC,
+ BPF_MAP_ARRAY_TYPE_LANDLOCK_FS,
};
enum bpf_map_handle_type {
BPF_MAP_HANDLE_TYPE_UNSPEC,
+ BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD,
+ BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_GLOB,
+};
+
+enum bpf_map_array_op {
+ BPF_MAP_ARRAY_OP_UNSPEC,
+ BPF_MAP_ARRAY_OP_OR,
+ BPF_MAP_ARRAY_OP_AND,
+ BPF_MAP_ARRAY_OP_XOR,
};
enum bpf_prog_type {
@@ -325,6 +335,35 @@ enum bpf_func_id {
*/
BPF_FUNC_skb_get_tunnel_opt,
BPF_FUNC_skb_set_tunnel_opt,
+
+ /**
+ * bpf_landlock_cmp_fs_prop_with_struct_file(prop, map, map_op, file)
+ * Compare file system handles with a struct file
+ *
+ * @prop: properties to check against (e.g. LANDLOCK_FLAG_FS_DENTRY)
+ * @map: handles to compare against
+ * @map_op: which elements of the map to use (e.g. BPF_MAP_ARRAY_OP_OR)
+ * @file: struct file address to compare with (taken from the context)
+ *
+ * Return: 0 if the file match the handles, 1 otherwise, or a negative
+ * value if an error occurred.
+ */
+ BPF_FUNC_landlock_cmp_fs_prop_with_struct_file,
+
+ /**
+ * bpf_landlock_cmp_fs_beneath_with_struct_file(opt, map, map_op, file)
+ * Check if a struct file is a leaf of file system handles
+ *
+ * @opt: check options (e.g. LANDLOCK_FLAG_OPT_REVERSE)
+ * @map: handles to compare against
+ * @map_op: which elements of the map to use (e.g. BPF_MAP_ARRAY_OP_OR)
+ * @file: struct file address to compare with (taken from the context)
+ *
+ * Return: 0 if the file is the same or beneath the handles,
+ * 1 otherwise, or a negative value if an error occurred.
+ */
+ BPF_FUNC_landlock_cmp_fs_beneath_with_struct_file,
+
__BPF_FUNC_MAX_ID,
};
@@ -398,6 +437,17 @@ struct bpf_tunnel_key {
__u32 tunnel_label;
};
+/* Handle check flags */
+#define LANDLOCK_FLAG_FS_DENTRY (1 << 0)
+#define LANDLOCK_FLAG_FS_INODE (1 << 1)
+#define LANDLOCK_FLAG_FS_DEVICE (1 << 2)
+#define LANDLOCK_FLAG_FS_MOUNT (1 << 3)
+#define _LANDLOCK_FLAG_FS_MASK ((1 << 4) - 1)
+
+/* Handle option flags */
+#define LANDLOCK_FLAG_OPT_REVERSE (1<<0)
+#define _LANDLOCK_FLAG_OPT_MASK ((1 << 1) - 1)
+
/* Map handle entry */
struct landlock_handle {
__u32 type; /* enum bpf_map_handle_type */
@@ -410,7 +460,7 @@ struct landlock_handle {
/**
* struct landlock_data
*
- * @hook: LSM hook ID
+ * @hook: LSM hook ID (e.g. BPF_PROG_TYPE_LANDLOCK_FILE_OPEN)
* @cookie: value set by a seccomp-filter return value RET_LANDLOCK. This come
* from a trusted seccomp-bpf program: the same process that loaded
* this Landlock hook program.
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 5938b8ee475b..6804dafd8355 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -508,7 +508,12 @@ static struct bpf_map *landlock_array_map_alloc(union
bpf_attr *attr)
static void landlock_put_handle(struct map_landlock_handle *handle)
{
switch (handle->type) {
- /* TODO: add handle types */
+ case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD:
+ if (likely(handle->file))
+ fput(handle->file);
+ else
+ WARN_ON(1);
+ break;
default:
WARN_ON(1);
}
@@ -533,7 +538,9 @@ static enum bpf_map_array_type landlock_get_array_type(
enum bpf_map_handle_type handle_type)
{
switch (handle_type) {
- /* TODO: add handle types */
+ case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD:
+ case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_GLOB:
+ return BPF_MAP_ARRAY_TYPE_LANDLOCK_FS;
case BPF_MAP_HANDLE_TYPE_UNSPEC:
default:
return -EINVAL;
@@ -550,6 +557,7 @@ static inline long landlock_store_handle(struct
map_landlock_handle *dst,
struct landlock_handle *khandle)
{
struct path kpath;
+ struct file *handle_file;
if (unlikely(!khandle))
return -EINVAL;
@@ -557,7 +565,10 @@ static inline long landlock_store_handle(struct
map_landlock_handle *dst,
/* access control already done for the FD */
switch (khandle->type) {
- /* TODO: add handle types */
+ case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD:
+ FGET_OR_RET(handle_file, khandle->fd);
+ dst->file = handle_file;
+ break;
default:
WARN_ON(1);
path_put(&kpath);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2931e2efcc10..b182c88d5c13 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -246,6 +246,7 @@ static const char * const reg_type_str[] = {
[PTR_TO_PACKET_END] = "pkt_end",
[PTR_TO_STRUCT_FILE] = "struct_file",
[PTR_TO_STRUCT_CRED] = "struct_cred",
+ [CONST_PTR_TO_LANDLOCK_HANDLE_FS] = "landlock_handle_fs",
};
static void print_verifier_state(struct verifier_state *state)
@@ -558,6 +559,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
case CONST_PTR_TO_MAP:
case PTR_TO_STRUCT_FILE:
case PTR_TO_STRUCT_CRED:
+ case CONST_PTR_TO_LANDLOCK_HANDLE_FS:
return true;
default:
return false;
@@ -951,6 +953,8 @@ static int check_func_arg(struct verifier_env *env, u32
regno,
expected_type = PTR_TO_STRUCT_FILE;
} else if (arg_type == ARG_PTR_TO_STRUCT_CRED) {
expected_type = PTR_TO_STRUCT_CRED;
+ } else if (arg_type == ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS) {
+ expected_type = CONST_PTR_TO_LANDLOCK_HANDLE_FS;
} else if (arg_type == ARG_PTR_TO_STACK ||
arg_type == ARG_PTR_TO_RAW_STACK) {
expected_type = PTR_TO_STACK;
@@ -1727,6 +1731,8 @@ static struct bpf_map *ld_imm64_to_map_ptr(struct
bpf_insn *insn)
static inline enum bpf_reg_type bpf_reg_type_from_map(struct bpf_map *map)
{
switch (map->map_array_type) {
+ case BPF_MAP_ARRAY_TYPE_LANDLOCK_FS:
+ return CONST_PTR_TO_LANDLOCK_HANDLE_FS;
case BPF_MAP_ARRAY_TYPE_UNSPEC:
default:
return CONST_PTR_TO_MAP;
diff --git a/security/landlock/Makefile b/security/landlock/Makefile
index 59669d70bc7e..27f359a8cfaa 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -1,3 +1,3 @@
obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
-landlock-y := lsm.o
+landlock-y := lsm.o checker_fs.o
diff --git a/security/landlock/checker_fs.c b/security/landlock/checker_fs.c
new file mode 100644
index 000000000000..4d2f1e5d41b6
--- /dev/null
+++ b/security/landlock/checker_fs.c
@@ -0,0 +1,183 @@
+/*
+ * Landlock LSM - File System Checkers
+ *
+ * Copyright (C) 2016 Mickaël Salaün <m...@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_map_array_op */
+#include <linux/errno.h>
+#include <linux/fs.h> /* path_is_under() */
+#include <linux/path.h> /* struct path */
+
+#include "checker_fs.h"
+
+#define EQUAL_NOT_NULL(a, b) (a && a == b)
+
+/*
+ * bpf_landlock_cmp_fs_prop_with_struct_file
+ *
+ * Cf. include/uapi/linux/bpf.h
+ */
+static inline u64 bpf_landlock_cmp_fs_prop_with_struct_file(u64 r1_property,
+ u64 r2_map, u64 r3_map_op, u64 r4_file, u64 r5)
+{
+ u8 property = (u8) r1_property;
+ struct bpf_map *map = (struct bpf_map *) (unsigned long) r2_map;
+ enum bpf_map_array_op map_op = r3_map_op;
+ struct file *file = (struct file *) (unsigned long) r4_file;
+ struct bpf_array *array = container_of(map, struct bpf_array, map);
+ struct path *p1, *p2;
+ struct map_landlock_handle *handle;
+ int i;
+ bool result_dentry = !(property & LANDLOCK_FLAG_FS_DENTRY);
+ bool result_inode = !(property & LANDLOCK_FLAG_FS_INODE);
+ bool result_device = !(property & LANDLOCK_FLAG_FS_DEVICE);
+ bool result_mount = !(property & LANDLOCK_FLAG_FS_MOUNT);
+
+ /* ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS is a arraymap */
+ if (unlikely(!map)) {
+ WARN_ON(1);
+ return -EFAULT;
+ }
+ if (unlikely(!file))
+ return -ENOENT;
+ if (unlikely((property | _LANDLOCK_FLAG_FS_MASK) !=
_LANDLOCK_FLAG_FS_MASK))
+ return -EINVAL;
+
+ /* for now, only handle OP_OR */
+ switch (map_op) {
+ case BPF_MAP_ARRAY_OP_OR:
+ break;
+ case BPF_MAP_ARRAY_OP_UNSPEC:
+ case BPF_MAP_ARRAY_OP_AND:
+ case BPF_MAP_ARRAY_OP_XOR:
+ default:
+ return -EINVAL;
+ }
+
+ synchronize_rcu();
+
+ for (i = 0; i < array->n_entries; i++) {
+ handle = (struct map_landlock_handle *)
+ (array->value + array->elem_size * i);
+
+ if (handle->type != BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) {
+ WARN_ON(1);
+ return -EFAULT;
+ }
+
+ p1 = &handle->file->f_path;
+ p2 = &file->f_path;
+ if (unlikely(!p1 || !p2)) {
+ WARN_ON(1);
+ return -EFAULT;
+ }
+
+ if (!result_dentry && p1->dentry == p2->dentry)
+ result_dentry = true;
+ /* TODO: use d_inode_rcu() instead? */
+ if (!result_inode
+ && EQUAL_NOT_NULL(d_inode(p1->dentry)->i_ino,
+ d_inode(p2->dentry)->i_ino))
+ result_inode = true;
+ /* check superblock instead of device major/minor */
+ if (!result_device
+ && EQUAL_NOT_NULL(d_inode(p1->dentry)->i_sb,
+ d_inode(p2->dentry)->i_sb))
+ result_device = true;
+ if (!result_mount && EQUAL_NOT_NULL(p1->mnt, p2->mnt))
+ result_mount = true;
+ if (result_dentry && result_inode && result_device &&
result_mount)
+ return 0;
+ }
+ return 1;
+}
+
+const struct bpf_func_proto bpf_landlock_cmp_fs_prop_with_struct_file_proto = {
+ .func = bpf_landlock_cmp_fs_prop_with_struct_file,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_ANYTHING,
+ .arg2_type = ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS,
+ .arg3_type = ARG_ANYTHING,
+ .arg4_type = ARG_PTR_TO_STRUCT_FILE,
+};
+
+/*
+ * bpf_landlock_cmp_fs_beneath_with_struct_file
+ *
+ * Cf. include/uapi/linux/bpf.h
+ */
+static inline u64 bpf_landlock_cmp_fs_beneath_with_struct_file(u64 r1_option,
+ u64 r2_map, u64 r3_map_op, u64 r4_file, u64 r5)
+{
+ u8 option = (u8) r1_option;
+ struct bpf_map *map = (struct bpf_map *) (unsigned long) r2_map;
+ enum bpf_map_array_op map_op = r3_map_op;
+ struct file *file = (struct file *) (unsigned long) r4_file;
+ struct bpf_array *array = container_of(map, struct bpf_array, map);
+ struct path *p1, *p2;
+ struct map_landlock_handle *handle;
+ int i;
+
+ /* ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS is an arraymap */
+ if (unlikely(!map)) {
+ WARN_ON(1);
+ return -EFAULT;
+ }
+ /* @file can be null for anonymous mmap */
+ if (unlikely(!file))
+ return -ENOENT;
+ if (unlikely((option | _LANDLOCK_FLAG_OPT_MASK) !=
_LANDLOCK_FLAG_OPT_MASK))
+ return -EINVAL;
+
+ /* for now, only handle OP_OR */
+ switch (map_op) {
+ case BPF_MAP_ARRAY_OP_OR:
+ break;
+ case BPF_MAP_ARRAY_OP_UNSPEC:
+ case BPF_MAP_ARRAY_OP_AND:
+ case BPF_MAP_ARRAY_OP_XOR:
+ default:
+ return -EINVAL;
+ }
+
+ synchronize_rcu();
+
+ for (i = 0; i < array->n_entries; i++) {
+ handle = (struct map_landlock_handle *)
+ (array->value + array->elem_size * i);
+
+ /* protected by the proto types, should not happen */
+ if (unlikely(handle->type !=
BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD)) {
+ WARN_ON(1);
+ return -EINVAL;
+ }
+
+ if (option & LANDLOCK_FLAG_OPT_REVERSE) {
+ p1 = &file->f_path;
+ p2 = &handle->file->f_path;
+ } else {
+ p1 = &handle->file->f_path;
+ p2 = &file->f_path;
+ }
+
+ if (path_is_under(p2, p1))
+ return 0;
+ }
+ return 1;
+}
+
+const struct bpf_func_proto bpf_landlock_cmp_fs_beneath_with_struct_file_proto
= {
+ .func = bpf_landlock_cmp_fs_beneath_with_struct_file,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_ANYTHING,
+ .arg2_type = ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS,
+ .arg3_type = ARG_ANYTHING,
+ .arg4_type = ARG_PTR_TO_STRUCT_FILE,
+};
diff --git a/security/landlock/checker_fs.h b/security/landlock/checker_fs.h
new file mode 100644
index 000000000000..a62f84e39efd
--- /dev/null
+++ b/security/landlock/checker_fs.h
@@ -0,0 +1,20 @@
+/*
+ * Landlock LSM - File System Checkers
+ *
+ * Copyright (C) 2016 Mickaël Salaün <m...@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_CHECKER_FS_H
+#define _SECURITY_LANDLOCK_CHECKER_FS_H
+
+#include <linux/fs.h>
+#include <linux/seccomp.h>
+
+extern const struct bpf_func_proto
bpf_landlock_cmp_fs_prop_with_struct_file_proto;
+extern const struct bpf_func_proto
bpf_landlock_cmp_fs_beneath_with_struct_file_proto;
+
+#endif /* _SECURITY_LANDLOCK_CHECKER_FS_H */
diff --git a/security/landlock/lsm.c b/security/landlock/lsm.c
index 322309068066..8645743243b6 100644
--- a/security/landlock/lsm.c
+++ b/security/landlock/lsm.c
@@ -16,6 +16,8 @@
#include <linux/lsm_hooks.h>
#include <linux/seccomp.h> /* struct seccomp_* */
+#include "checker_fs.h"
+
#define LANDLOCK_HOOK_INIT(NAME) LSM_HOOK_INIT(NAME, landlock_hook_##NAME)
#define LANDLOCK_HOOKx(X, NAME, CNAME, ...) \
@@ -117,7 +119,14 @@ static int landlock_run_prog(__u64 args[6])
static const struct bpf_func_proto *bpf_landlock_func_proto(
enum bpf_func_id func_id)
{
- return NULL;
+ switch (func_id) {
+ case BPF_FUNC_landlock_cmp_fs_prop_with_struct_file:
+ return &bpf_landlock_cmp_fs_prop_with_struct_file_proto;
+ case BPF_FUNC_landlock_cmp_fs_beneath_with_struct_file:
+ return &bpf_landlock_cmp_fs_beneath_with_struct_file_proto;
+ default:
+ return NULL;
+ }
}
static u32 landlock_convert_ctx_access(enum bpf_access_type type, int dst_reg,
--
2.8.1
