Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933433AbcJZHAn (ORCPT ); Wed, 26 Oct 2016 03:00:43 -0400 Received: from smtp-sh2.infomaniak.ch ([128.65.195.6]:54714 "EHLO smtp-sh2.infomaniak.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754701AbcJZG6j (ORCPT ); Wed, 26 Oct 2016 02:58:39 -0400 From: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= , Alexei Starovoitov , Andy Lutomirski , Daniel Borkmann , Daniel Mack , David Drysdale , "David S . Miller" , "Eric W . Biederman" , James Morris , Jann Horn , Kees Cook , Paul Moore , Sargun Dhillon , "Serge E . Hallyn" , Tejun Heo , Thomas Graf , Will Drewry , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org, netdev@vger.kernel.org, cgroups@vger.kernel.org Subject: [RFC v4 08/18] landlock: Handle file comparisons Date: Wed, 26 Oct 2016 08:56:44 +0200 Message-Id: <20161026065654.19166-9-mic@digikod.net> X-Mailer: git-send-email 2.9.3 In-Reply-To: <20161026065654.19166-1-mic@digikod.net> References: <20161026065654.19166-1-mic@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 12710 Lines: 396 Add eBPF functions to compare file system access with a Landlock file system handle: * bpf_landlock_cmp_fs_beneath(opt, map, map_op, fs_arg) This function allows an eBPF program to check if the current accessed file is the same or in the hierarchy of a reference handle. * bpf_landlock_get_fs_mode(arg_fs) This function return the mode of a file. This is useful to check if a process try to walk through a directory. 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 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 Cc: Alexei Starovoitov Cc: Andy Lutomirski Cc: Daniel Borkmann Cc: David S. Miller Cc: James Morris Cc: Kees Cook Cc: Serge E. Hallyn Cc: Jann Horn Link: https://lkml.kernel.org/r/CALCETrWwTiz3kZTkEgOW24-DvhQq6LftwEXh77FD2G5o71yD7g@mail.gmail.com Link: https://lkml.kernel.org/r/20160914190723.GB5617@pc.thejh.net --- include/linux/bpf.h | 5 ++ include/uapi/linux/bpf.h | 35 ++++++++++ samples/bpf/bpf_helpers.h | 5 ++ security/landlock/Makefile | 2 +- security/landlock/checker_fs.c | 152 +++++++++++++++++++++++++++++++++++++++++ security/landlock/checker_fs.h | 20 ++++++ security/landlock/common.h | 13 ++++ security/landlock/lsm.c | 6 ++ 8 files changed, 237 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 e7ce49642f50..50fbeaac03fe 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -363,6 +363,11 @@ 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_beneath_proto; +extern const struct bpf_func_proto bpf_landlock_get_fs_mode_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 b6b531a868c0..5f09eda3ab68 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -101,6 +101,13 @@ enum bpf_map_handle_type { /* 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 { BPF_PROG_TYPE_UNSPEC, BPF_PROG_TYPE_SOCKET_FILTER, @@ -465,6 +472,30 @@ enum bpf_func_id { */ BPF_FUNC_set_hash_invalid, + /** + * bpf_landlock_cmp_fs_beneath(opt, map, map_op, arg_fs) + * Check if a struct inode 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) + * @arg_fs: struct landlock_arg_fs address to compare with + * + * 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, + + /** + * bpf_landlock_get_fs_mode(arg_fs) + * Get the mode of a struct landlock_arg_fs + * + * @arg_fs: struct landlock_arg_fs address + * + * Return: the file mode + */ + BPF_FUNC_landlock_get_fs_mode, + __BPF_FUNC_MAX_ID, }; @@ -583,6 +614,10 @@ enum landlock_hook { */ #define _LANDLOCK_SUBTYPE_OPTION_MASK ((1ULL << 0) - 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/samples/bpf/bpf_helpers.h b/samples/bpf/bpf_helpers.h index 90f44bd2045e..52fa1ab1c0c4 100644 --- a/samples/bpf/bpf_helpers.h +++ b/samples/bpf/bpf_helpers.h @@ -57,6 +57,11 @@ static int (*bpf_skb_set_tunnel_opt)(void *ctx, void *md, int size) = (void *) BPF_FUNC_skb_set_tunnel_opt; static unsigned long long (*bpf_get_prandom_u32)(void) = (void *) BPF_FUNC_get_prandom_u32; +static unsigned long long (*bpf_landlock_cmp_fs_beneath) + (int option, void *map, int map_op, void *arg_fs) = + (void *) BPF_FUNC_landlock_cmp_fs_beneath; +static unsigned long long (*bpf_landlock_get_fs_mode)(void *arg_fs) = + (void *) BPF_FUNC_landlock_get_fs_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/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..01a929a269e6 --- /dev/null +++ b/security/landlock/checker_fs.c @@ -0,0 +1,152 @@ +/* + * Landlock LSM - File System Checkers + * + * Copyright (C) 2016 Mickaël Salaün + * + * 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 /* enum bpf_map_array_op */ +#include +#include /* BPF_CALL*() */ +#include /* path_is_under() */ +#include /* struct path */ + +#include "common.h" /* struct landlock_arg_fs */ +#include "checker_fs.h" + +/* + * bpf_landlock_cmp_fs_beneath + * + * Cf. include/uapi/linux/bpf.h + */ +BPF_CALL_4(bpf_landlock_cmp_fs_beneath, u8, option, struct bpf_map *, map, + enum bpf_map_array_op, map_op, + struct landlock_arg_fs *, arg_fs) +{ + struct bpf_array *array = container_of(map, struct bpf_array, map); + const struct path *p1 = NULL, *p2 = NULL; + struct dentry *d1 = NULL, *d2 = NULL; + struct map_landlock_handle *handle; + size_t i; + + if (WARN_ON(!map)) + return -EFAULT; + if (WARN_ON(!arg_fs)) + return -EFAULT; + if (unlikely((option | _LANDLOCK_FLAG_OPT_MASK) != _LANDLOCK_FLAG_OPT_MASK)) + return -EINVAL; + + if (!arg_fs->file) { + /* file can be null for anonymous mmap */ + WARN_ON(arg_fs->type != LANDLOCK_ARGTYPE_FILE); + return -ENOENT; + } + + /* 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; + } + switch (arg_fs->type) { + case LANDLOCK_ARGTYPE_FILE: + p1 = &arg_fs->file->f_path; + break; + case LANDLOCK_ARGTYPE_PATH: + p1 = arg_fs->path; + break; + case LANDLOCK_ARGTYPE_INODE: + d1 = d_find_alias(arg_fs->inode); + if (WARN_ON(!d1)) + return -ENOENT; + break; + case LANDLOCK_ARGTYPE_NONE: + default: + WARN_ON(1); + return -EFAULT; + } + /* {p,d}1 and {p,d}2 will be set correctly in the loop */ + p2 = p1; + d2 = d1; + + if (p1) { + for_each_handle(i, handle, array) { + if (WARN_ON(handle->type != BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD)) + return -EINVAL; + + if (option & LANDLOCK_FLAG_OPT_REVERSE) + p2 = &handle->path; + else + p1 = &handle->path; + + if (path_is_under(p2, p1)) + return 0; + } + } else if (d1) { + for_each_handle(i, handle, array) { + if (WARN_ON(handle->type != BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD)) + return -EINVAL; + + if (option & LANDLOCK_FLAG_OPT_REVERSE) + d2 = handle->path.dentry; + else + d1 = handle->path.dentry; + + if (is_subdir(d2, d1)) + return 0; + } + } + return 1; +} + +const struct bpf_func_proto bpf_landlock_cmp_fs_beneath_proto = { + .func = bpf_landlock_cmp_fs_beneath, + .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_CONST_PTR_TO_LANDLOCK_ARG_FS, +}; + +BPF_CALL_1(bpf_landlock_get_fs_mode, struct landlock_arg_fs *, arg_fs) +{ + if (WARN_ON(!arg_fs)) + return -EFAULT; + if (!arg_fs->file) { + /* file can be null for anonymous mmap */ + WARN_ON(arg_fs->type != LANDLOCK_ARGTYPE_FILE); + return -ENOENT; + } + switch (arg_fs->type) { + case LANDLOCK_ARGTYPE_FILE: + if (WARN_ON(!arg_fs->file->f_inode)) + return -ENOENT; + return arg_fs->file->f_inode->i_mode; + case LANDLOCK_ARGTYPE_INODE: + return arg_fs->inode->i_mode; + case LANDLOCK_ARGTYPE_PATH: + if (WARN_ON(!arg_fs->path->dentry || + !arg_fs->path->dentry->d_inode)) + return -ENOENT; + return arg_fs->path->dentry->d_inode->i_mode; + case LANDLOCK_ARGTYPE_NONE: + default: + WARN_ON(1); + return -EFAULT; + } +} + +const struct bpf_func_proto bpf_landlock_get_fs_mode_proto = { + .func = bpf_landlock_get_fs_mode, + .gpl_only = true, + .ret_type = RET_INTEGER, + .arg1_type = ARG_CONST_PTR_TO_LANDLOCK_ARG_FS, +}; diff --git a/security/landlock/checker_fs.h b/security/landlock/checker_fs.h new file mode 100644 index 000000000000..8bcdc9cba2b8 --- /dev/null +++ b/security/landlock/checker_fs.h @@ -0,0 +1,20 @@ +/* + * Landlock LSM - File System Checkers + * + * Copyright (C) 2016 Mickaël Salaün + * + * 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 +#include + +extern const struct bpf_func_proto bpf_landlock_cmp_fs_beneath_proto; +extern const struct bpf_func_proto bpf_landlock_get_fs_mode_proto; + +#endif /* _SECURITY_LANDLOCK_CHECKER_FS_H */ diff --git a/security/landlock/common.h b/security/landlock/common.h index dd64e6391dd8..a30aa93dc1ae 100644 --- a/security/landlock/common.h +++ b/security/landlock/common.h @@ -15,6 +15,19 @@ #include /* struct file, struct inode */ #include /* struct path */ +/** + * for_each_handle - iterate over all handles of an arraymap + * + * @i: index in the arraymap + * @handle: struct map_landlock_handle pointer + * @array: struct bpf_array pointer to walk through + */ +#define for_each_handle(i, handle, array) \ + for (i = 0; i < atomic_read(&array->n_entries) && \ + (handle = *((struct map_landlock_handle **) \ + (array->value + array->elem_size * i)));\ + i++) + enum landlock_argtype { LANDLOCK_ARGTYPE_NONE, LANDLOCK_ARGTYPE_FILE, diff --git a/security/landlock/lsm.c b/security/landlock/lsm.c index b3d154275be6..b3c107244df9 100644 --- a/security/landlock/lsm.c +++ b/security/landlock/lsm.c @@ -22,6 +22,7 @@ #include /* struct inode */ #include /* struct path */ +#include "checker_fs.h" #include "common.h" #define MAP0(s, m, ...) @@ -170,6 +171,11 @@ 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_get_fs_mode: + return &bpf_landlock_get_fs_mode_proto; + case BPF_FUNC_landlock_cmp_fs_beneath: + return &bpf_landlock_cmp_fs_beneath_proto; + default: return NULL; } -- 2.9.3