[kernel-hardening] [PATCH v5 03/10] bpf: Define handle_fs and add a new helper bpf_handle_fs_get_mode()

Mickaël Salaün
2017-02-22T01:26:25Z

Add an eBPF function bpf_handle_fs_get_mode(handle_fs) to get the mode
of a an abstract object wrapping either a file, a dentry, a path, or an
inode.

Changes since v4:
* use a file abstraction (handle) to wrap inode, dentry, path and file
structs
* remove bpf_landlock_cmp_fs_beneath()
* rename the BPF helper and move it to kernel/bpf/
* tighten helpers accessible by a Landlock rule

Changes since v3:
* remove bpf_landlock_cmp_fs_prop() (suggested by Alexie Starovoitov)
* add hooks dealing with struct inode and struct path pointers:
inode_permission and inode_getattr
* add abstraction over eBPF helper arguments thanks to wrapping structs
* add bpf_landlock_get_fs_mode() helper to check file type and mode
* merge WARN_ON() (suggested by Kees Cook)
* fix and update bpf_helpers.h
* use BPF_CALL_* for eBPF helpers (suggested by Alexie Starovoitov)
* make handle arraymap safe (RCU) and remove buggy synchronize_rcu()
* factor out the arraymay walk
* use size_t to index array (suggested by Jann Horn)

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>
Cc: Jann Horn <jann@thejh.net>
---
include/linux/bpf.h | 33 +++++++++++++++++++++++++++
include/uapi/linux/bpf.h | 10 +++++++-
kernel/bpf/Makefile | 2 +-
kernel/bpf/helpers_fs.c | 52 ++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 6 +++++
samples/bpf/bpf_helpers.h | 2 ++
security/landlock/hooks.c | 8 ++++++-
tools/include/uapi/linux/bpf.h | 10 +++++++-
8 files changed, 119 insertions(+), 4 deletions(-)
create mode 100644 kernel/bpf/helpers_fs.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index dd954048aa19..bc01a7388168 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -15,6 +15,11 @@
#include <linux/err.h>
#include <linux/rbtree_latch.h>

+/* FS helpers */
+#include <linux/dcache.h> /* struct dentry */
+#include <linux/fs.h> /* struct file, struct inode */
+#include <linux/path.h> /* struct path */
+
struct perf_event;
struct bpf_map;

@@ -82,6 +87,8 @@ enum bpf_arg_type {

ARG_PTR_TO_CTX, /* pointer to context */
ARG_ANYTHING, /* any (initialized) argument is ok */
+
+ ARG_CONST_PTR_TO_HANDLE_FS, /* pointer to an abstract FS struct */
};

/* type of values returned from helper functions */
@@ -148,6 +155,9 @@ enum bpf_reg_type {
* map element.
*/
PTR_TO_MAP_VALUE_ADJ,
+
+ /* FS helpers */
+ CONST_PTR_TO_HANDLE_FS,
};

struct bpf_prog;
@@ -220,6 +230,26 @@ struct bpf_event_entry {
struct rcu_head rcu;
};

+/* FS helpers */
+enum bpf_handle_fs_type {
+ BPF_HANDLE_FS_TYPE_NONE,
+ BPF_HANDLE_FS_TYPE_FILE,
+ BPF_HANDLE_FS_TYPE_INODE,
+ BPF_HANDLE_FS_TYPE_PATH,
+ BPF_HANDLE_FS_TYPE_DENTRY,
+};
+
+struct bpf_handle_fs {
+ enum bpf_handle_fs_type type;
+ union {
+ struct file *file;
+ struct inode *inode;
+ const struct path *path;
+ struct dentry *dentry;
+ };
+};
+
+
u64 bpf_tail_call(u64 ctx, u64 r2, u64 index, u64 r4, u64 r5);
u64 bpf_get_stackid(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);

@@ -358,6 +388,9 @@ 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;

+/* FS helpers */
+extern const struct bpf_func_proto bpf_handle_fs_get_mode_proto;
+
/* 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 c9c909a84f0b..ffceb42ccc4e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -467,6 +467,13 @@ union bpf_attr {
* Return:
* > 0 length of the string including the trailing NUL on success
* < 0 error
+ *
+ * s64 bpf_handle_fs_get_mode(handle_fs)
+ * Get the mode of a struct bpf_handle_fs
+ * fs: struct bpf_handle_fs address
+ * Return:
+ * >= 0 file mode
+ * < 0 error
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -514,7 +521,8 @@ union bpf_attr {
FN(get_numa_node_id), \
FN(skb_change_head), \
FN(xdp_adjust_head), \
- FN(probe_read_str),
+ FN(probe_read_str), \
+ FN(handle_fs_get_mode),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index e1ce4f4fd7fd..be090e802aa5 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -1,6 +1,6 @@
obj-y := core.o

-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o helpers_fs.o
obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o
ifeq ($(CONFIG_PERF_EVENTS),y)
obj-$(CONFIG_BPF_SYSCALL) += stackmap.o
diff --git a/kernel/bpf/helpers_fs.c b/kernel/bpf/helpers_fs.c
new file mode 100644
index 000000000000..8166b5b42cd7
--- /dev/null
+++ b/kernel/bpf/helpers_fs.c
@@ -0,0 +1,52 @@
+/*
+ * BPF filesystem helpers
+ *
+ * Copyright © 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> /* struct bpf_handle_fs */
+#include <linux/errno.h>
+#include <linux/filter.h> /* BPF_CALL*() */
+
+BPF_CALL_1(bpf_handle_fs_get_mode, struct bpf_handle_fs *, handle_fs)
+{
+ if (WARN_ON(!handle_fs))
+ return -EFAULT;
+ if (!handle_fs->file) {
+ /* file can be null for anonymous mmap */
+ WARN_ON(handle_fs->type != BPF_HANDLE_FS_TYPE_FILE);
+ return -ENOENT;
+ }
+ switch (handle_fs->type) {
+ case BPF_HANDLE_FS_TYPE_FILE:
+ if (WARN_ON(!handle_fs->file->f_inode))
+ return -ENOENT;
+ return handle_fs->file->f_inode->i_mode;
+ case BPF_HANDLE_FS_TYPE_INODE:
+ return handle_fs->inode->i_mode;
+ case BPF_HANDLE_FS_TYPE_PATH:
+ if (WARN_ON(!handle_fs->path->dentry ||
+ !handle_fs->path->dentry->d_inode))
+ return -ENOENT;
+ return handle_fs->path->dentry->d_inode->i_mode;
+ case BPF_HANDLE_FS_TYPE_DENTRY:
+ if (WARN_ON(!handle_fs->dentry->d_inode))
+ return -ENOENT;
+ return handle_fs->dentry->d_inode->i_mode;
+ case BPF_HANDLE_FS_TYPE_NONE:
+ default:
+ WARN_ON(1);
+ return -EFAULT;
+ }
+}
+
+const struct bpf_func_proto bpf_handle_fs_get_mode_proto = {
+ .func = bpf_handle_fs_get_mode,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_CONST_PTR_TO_HANDLE_FS,
+};
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fe26ec007a9a..ab0d4fbba399 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -189,6 +189,7 @@ static const char * const reg_type_str[] = {
[CONST_IMM] = "imm",
[PTR_TO_PACKET] = "pkt",
[PTR_TO_PACKET_END] = "pkt_end",
+ [CONST_PTR_TO_HANDLE_FS] = "handle_fs",
};

#define __BPF_FUNC_STR_FN(x) [BPF_FUNC_ ## x] = __stringify(bpf_ ## x)
@@ -546,6 +547,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
case PTR_TO_PACKET_END:
case FRAME_PTR:
case CONST_PTR_TO_MAP:
+ case CONST_PTR_TO_HANDLE_FS:
return true;
default:
return false;
@@ -1052,6 +1054,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
expected_type = PTR_TO_CTX;
if (type != expected_type)
goto err_type;
+ } else if (arg_type == ARG_CONST_PTR_TO_HANDLE_FS) {
+ expected_type = CONST_PTR_TO_HANDLE_FS;
+ if (type != expected_type)
+ goto err_type;
} else if (arg_type == ARG_PTR_TO_MEM ||
arg_type == ARG_PTR_TO_UNINIT_MEM) {
expected_type = PTR_TO_STACK;
diff --git a/samples/bpf/bpf_helpers.h b/samples/bpf/bpf_helpers.h
index faaffe2e139a..323e4b13d1d1 100644
--- a/samples/bpf/bpf_helpers.h
+++ b/samples/bpf/bpf_helpers.h
@@ -59,6 +59,8 @@ static unsigned long long (*bpf_get_prandom_u32)(void) =
(void *) BPF_FUNC_get_prandom_u32;
static int (*bpf_xdp_adjust_head)(void *ctx, int offset) =
(void *) BPF_FUNC_xdp_adjust_head;
+static long long (*bpf_handle_fs_get_mode)(void *handle_fs) =
+ (void *) BPF_FUNC_handle_fs_get_mode;

/* llvm builtin functions that eBPF C program may use to
* emit BPF_LD_ABS and BPF_LD_IND instructions
diff --git a/security/landlock/hooks.c b/security/landlock/hooks.c
index 28a26bd8c1a2..6c1ad0e03cfc 100644
--- a/security/landlock/hooks.c
+++ b/security/landlock/hooks.c
@@ -11,7 +11,7 @@
#include <asm/current.h>
#include <asm/processor.h> /* task_pt_regs() */
#include <asm/syscall.h> /* syscall_get_nr(), syscall_get_arch() */
-#include <linux/bpf.h> /* enum bpf_access_type, enum bpf_*, enum landlock_subtype_event, struct landlock_context, struct bpf_handle_fs */
+#include <linux/bpf.h> /* enum bpf_access_type, struct landlock_context */
#include <linux/err.h> /* EPERM */
#include <linux/filter.h> /* struct bpf_prog, BPF_PROG_RUN() */
#include <linux/kernel.h> /* ARRAY_SIZE */
@@ -79,6 +79,12 @@ static inline const struct bpf_func_proto *bpf_landlock_func_proto(
case BPF_FUNC_map_lookup_elem:
return &bpf_map_lookup_elem_proto;

+ /* event_fs */
+ case BPF_FUNC_handle_fs_get_mode:
+ if (event_fs)
+ return &bpf_handle_fs_get_mode_proto;
+ return NULL;
+
/* ability_write */
case BPF_FUNC_map_delete_elem:
if (ability_write)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c9c909a84f0b..ffceb42ccc4e 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -467,6 +467,13 @@ union bpf_attr {
* Return:
* > 0 length of the string including the trailing NUL on success
* < 0 error
+ *
+ * s64 bpf_handle_fs_get_mode(handle_fs)
+ * Get the mode of a struct bpf_handle_fs
+ * fs: struct bpf_handle_fs address
+ * Return:
+ * >= 0 file mode
+ * < 0 error
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -514,7 +521,8 @@ union bpf_attr {
FN(get_numa_node_id), \
FN(skb_change_head), \
FN(xdp_adjust_head), \
- FN(probe_read_str),
+ FN(probe_read_str), \
+ FN(handle_fs_get_mode),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
--
2.11.0