[RFC,v3,07/22] landlock: Handle file comparisons

Message ID	20160914072415.26021-8-mic@digikod.net (mailing list archive)
State	New, archived
Headers	show Return-Path: <kernel-hardening-return-4587-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com> Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk Reply-To: kernel-hardening@lists.openwall.com From: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= <mic@digikod.net> To: linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= <mic@digikod.net>, Alexei Starovoitov <ast@kernel.org>, Andy Lutomirski <luto@amacapital.net>, Arnd Bergmann <arnd@arndb.de>, Casey Schaufler <casey@schaufler-ca.com>, Daniel Borkmann <daniel@iogearbox.net>, Daniel Mack <daniel@zonque.org>, David Drysdale <drysdale@google.com>, "David S . Miller" <davem@davemloft.net>, Elena Reshetova <elena.reshetova@intel.com>, "Eric W . Biederman" <ebiederm@xmission.com>, James Morris <james.l.morris@oracle.com>, Kees Cook <keescook@chromium.org>, Paul Moore <pmoore@redhat.com>, Sargun Dhillon <sargun@sargun.me>, "Serge E . Hallyn" <serge@hallyn.com>, Tejun Heo <tj@kernel.org>, Will Drewry <wad@chromium.org>, kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org, netdev@vger.kernel.org, cgroups@vger.kernel.org Date: Wed, 14 Sep 2016 09:24:00 +0200 Message-Id: <20160914072415.26021-8-mic@digikod.net> In-Reply-To: <20160914072415.26021-1-mic@digikod.net> References: <20160914072415.26021-1-mic@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: [kernel-hardening] [RFC v3 07/22] landlock: Handle file comparisons

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; }

[RFC,v3,07/22] landlock: Handle file comparisons

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