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Subject[RFC v3 07/22] landlock: Handle file comparisons
Date
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).

Changes since v2:
* add MNT_INTERNAL check to only add file handle from user-visible FS
(e.g. no anonymous inode)
* replace struct file* with struct path* in map_landlock_handle
* add BPF protos
* fix bpf_landlock_cmp_fs_prop_with_struct_file()

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>
Link: https://lkml.kernel.org/r/CALCETrWwTiz3kZTkEgOW24-DvhQq6LftwEXh77FD2G5o71yD7g@mail.gmail.com
---
include/linux/bpf.h | 10 +++
include/uapi/linux/bpf.h | 49 +++++++++++
kernel/bpf/arraymap.c | 21 +++++
kernel/bpf/verifier.c | 8 ++
security/landlock/Makefile | 2 +-
security/landlock/checker_fs.c | 179 +++++++++++++++++++++++++++++++++++++++++
security/landlock/checker_fs.h | 20 +++++
security/landlock/lsm.c | 6 ++
8 files changed, 294 insertions(+), 1 deletion(-)
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 36c3e482239c..f7325c17f720 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -87,6 +87,7 @@ enum bpf_arg_type {
ARG_ANYTHING, /* any (initialized) argument is ok */

ARG_PTR_TO_STRUCT_FILE, /* pointer to struct file */
+ ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS, /* pointer to Landlock FS handle */
};

/* type of values returned from helper functions */
@@ -148,6 +149,7 @@ enum bpf_reg_type {

/* Landlock */
PTR_TO_STRUCT_FILE,
+ CONST_PTR_TO_LANDLOCK_HANDLE_FS,
};

struct bpf_prog;
@@ -214,6 +216,9 @@ struct bpf_array {
#ifdef CONFIG_SECURITY_LANDLOCK
struct map_landlock_handle {
u32 type; /* enum bpf_map_handle_type */
+ union {
+ struct path path;
+ };
};
#endif /* CONFIG_SECURITY_LANDLOCK */

@@ -348,6 +353,11 @@ extern const struct bpf_func_proto bpf_skb_vlan_push_proto;
extern const struct bpf_func_proto bpf_skb_vlan_pop_proto;
extern const struct bpf_func_proto bpf_get_stackid_proto;

+#ifdef CONFIG_SECURITY_LANDLOCK
+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 /* CONFIG_SECURITY_LANDLOCK */
+
/* Shared helpers among cBPF and eBPF. */
void bpf_user_rnd_init_once(void);
u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ad87003fe892..905dcace7255 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -92,10 +92,20 @@ 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 {
@@ -434,6 +444,34 @@ enum bpf_func_id {
*/
BPF_FUNC_skb_change_tail,

+ /**
+ * 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,
};

@@ -546,6 +584,17 @@ enum landlock_hook_id {
/* context of function access flags */
#define _LANDLOCK_FLAG_ACCESS_MASK ((1ULL << 0) - 1)

+/* 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 ((1ULL << 4) - 1)
+
+/* Handle option flags */
+#define LANDLOCK_FLAG_OPT_REVERSE (1<<0)
+#define _LANDLOCK_FLAG_OPT_MASK ((1ULL << 1) - 1)
+
/* Map handle entry */
struct landlock_handle {
__u32 type; /* enum bpf_map_handle_type */
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 94256597eacd..edaab4c87292 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -21,6 +21,8 @@

#ifdef CONFIG_SECURITY_LANDLOCK
#include <asm/resource.h> /* RLIMIT_NOFILE */
+#include <linux/mount.h> /* struct vfsmount, MNT_INTERNAL */
+#include <linux/path.h> /* path_get(), path_put() */
#include <linux/sched.h> /* rlimit() */
#endif /* CONFIG_SECURITY_LANDLOCK */

@@ -603,6 +605,9 @@ static void landlock_put_handle(struct map_landlock_handle *handle)
enum bpf_map_handle_type handle_type = handle->type;

switch (handle_type) {
+ case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD:
+ path_put(&handle->path);
+ break;
case BPF_MAP_HANDLE_TYPE_UNSPEC:
default:
WARN_ON(1);
@@ -628,6 +633,8 @@ static enum bpf_map_array_type landlock_get_array_type(
enum bpf_map_handle_type handle_type)
{
switch (handle_type) {
+ case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD:
+ return BPF_MAP_ARRAY_TYPE_LANDLOCK_FS;
case BPF_MAP_HANDLE_TYPE_UNSPEC:
default:
return -EINVAL;
@@ -650,8 +657,22 @@ static inline long landlock_store_handle(struct map_landlock_handle *dst,
struct landlock_handle *handle)
{
enum bpf_map_handle_type handle_type = handle->type;
+ struct file *handle_file;
+
+ /* access control already done for the FD */

switch (handle_type) {
+ case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD:
+ FGET_OR_RET(handle_file, handle->fd);
+ /* check if the FD is tied to a user mount point */
+ if (unlikely(handle_file->f_path.mnt->mnt_flags & MNT_INTERNAL)) {
+ fput(handle_file);
+ return -EINVAL;
+ }
+ path_get(&handle_file->f_path);
+ dst->path = handle_file->f_path;
+ fput(handle_file);
+ break;
case BPF_MAP_HANDLE_TYPE_UNSPEC:
default:
WARN_ON(1);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5c9982d55612..8d7b18574f5a 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] = "pkt",
[PTR_TO_PACKET_END] = "pkt_end",
[PTR_TO_STRUCT_FILE] = "struct_file",
+ [CONST_PTR_TO_LANDLOCK_HANDLE_FS] = "landlock_handle_fs",
};

static void print_verifier_state(struct verifier_state *state)
@@ -557,6 +558,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
case FRAME_PTR:
case CONST_PTR_TO_MAP:
case PTR_TO_STRUCT_FILE:
+ case CONST_PTR_TO_LANDLOCK_HANDLE_FS:
return true;
default:
return false;
@@ -978,6 +980,10 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
expected_type = PTR_TO_STRUCT_FILE;
if (type != expected_type)
goto err_type;
+ } else if (arg_type == ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS) {
+ expected_type = CONST_PTR_TO_LANDLOCK_HANDLE_FS;
+ if (type != expected_type)
+ goto err_type;
} else if (arg_type == ARG_PTR_TO_STACK ||
arg_type == ARG_PTR_TO_RAW_STACK) {
expected_type = PTR_TO_STACK;
@@ -1801,6 +1807,8 @@ 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..39eb85dc7d18
--- /dev/null
+++ b/security/landlock/checker_fs.c
@@ -0,0 +1,179 @@
+/*
+ * Landlock LSM - File System Checkers
+ *
+ * Copyright (C) 2016 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_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;
+
+ /* ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS is an 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;
+ }
+ p2 = &file->f_path;
+
+ synchronize_rcu();
+
+ for (i = 0; i < array->n_entries; 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);
+
+ 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->path;
+
+ 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;
+ }
+ /* p1 and p2 will be set correctly in the loop */
+ p1 = &file->f_path;
+ p2 = p1;
+
+ 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)
+ p2 = &handle->path;
+ else
+ p1 = &handle->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 <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_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 c032183e5d95..952b7bc66328 100644
--- a/security/landlock/lsm.c
+++ b/security/landlock/lsm.c
@@ -17,6 +17,8 @@
#include <linux/lsm_hooks.h>
#include <linux/types.h> /* uintptr_t */

+#include "checker_fs.h"
+
#define LANDLOCK_MAP0(m, ...)
#define LANDLOCK_MAP1(m, d, t, a) m(d, t, a)
#define LANDLOCK_MAP2(m, d, t, a, ...) m(d, t, a), LANDLOCK_MAP1(m, __VA_ARGS__)
@@ -70,6 +72,10 @@ static const struct bpf_func_proto *bpf_landlock_func_proto(
enum bpf_func_id func_id, union bpf_prog_subtype *prog_subtype)
{
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;
}
--
2.9.3
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