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Subject[RFC v3 11/22] seccomp,landlock: Handle Landlock hooks per process hierarchy
Date
A Landlock program will be triggered according to its subtype/origin
bitfield. The LANDLOCK_FLAG_ORIGIN_SECCOMP value will trigger the
Landlock program when a seccomp filter will return RET_LANDLOCK.
Moreover, it is possible to return a 16-bit cookie which will be
readable by the Landlock programs in its context.

Only seccomp filters loaded from the same thread and before a Landlock
program can trigger it through LANDLOCK_FLAG_ORIGIN_SECCOMP. Multiple
Landlock programs can be triggered by one or more seccomp filters. This
way, each RET_LANDLOCK (with specific cookie) will trigger all the
allowed Landlock programs once.

Changes since v2:
* Landlock programs can now be run without seccomp filter but for any
syscall (from the process) or interruption
* move Landlock related functions and structs into security/landlock/*
(to manage cgroups as well)
* fix seccomp filter handling: run Landlock programs for each of their
legitimate seccomp filter
* properly clean up all seccomp results
* cosmetic changes to ease the understanding
* fix some ifdef

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/landlock.h | 77 ++++++++++++++
include/linux/seccomp.h | 26 +++++
include/uapi/linux/seccomp.h | 2 +
kernel/fork.c | 23 +++-
kernel/seccomp.c | 68 +++++++++++-
security/landlock/Makefile | 2 +-
security/landlock/common.h | 27 +++++
security/landlock/lsm.c | 96 ++++++++++++++++-
security/landlock/manager.c | 242 +++++++++++++++++++++++++++++++++++++++++++
9 files changed, 552 insertions(+), 11 deletions(-)
create mode 100644 include/linux/landlock.h
create mode 100644 security/landlock/common.h
create mode 100644 security/landlock/manager.c

diff --git a/include/linux/landlock.h b/include/linux/landlock.h
new file mode 100644
index 000000000000..932ae57fa70e
--- /dev/null
+++ b/include/linux/landlock.h
@@ -0,0 +1,77 @@
+/*
+ * Landlock LSM - Public headers
+ *
+ * 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 _LINUX_LANDLOCK_H
+#define _LINUX_LANDLOCK_H
+#ifdef CONFIG_SECURITY_LANDLOCK
+
+#include <linux/bpf.h> /* _LANDLOCK_HOOK_LAST */
+#include <linux/types.h> /* atomic_t */
+
+#ifdef CONFIG_SECCOMP_FILTER
+#include <linux/seccomp.h> /* struct seccomp_filter */
+#endif /* CONFIG_SECCOMP_FILTER */
+
+
+#ifdef CONFIG_SECCOMP_FILTER
+struct landlock_seccomp_ret {
+ struct landlock_seccomp_ret *prev;
+ struct seccomp_filter *filter;
+ u16 cookie;
+ bool triggered;
+};
+#endif /* CONFIG_SECCOMP_FILTER */
+
+struct landlock_rule {
+ atomic_t usage;
+ struct landlock_rule *prev;
+ /*
+ * List of filters (through filter->thread_prev) allowed to trigger
+ * this Landlock program.
+ */
+ struct bpf_prog *prog;
+#ifdef CONFIG_SECCOMP_FILTER
+ struct seccomp_filter *thread_filter;
+#endif /* CONFIG_SECCOMP_FILTER */
+};
+
+/**
+ * struct landlock_hooks - Landlock hook programs enforced on a thread
+ *
+ * This is used for low performance impact when forking a process. Instead of
+ * copying the full array and incrementing the usage field of each entries,
+ * only create a pointer to struct landlock_hooks and increment the usage
+ * field.
+ *
+ * A new struct landlock_hooks must be created thanks to a call to
+ * new_landlock_hooks().
+ *
+ * @usage: reference count to manage the object lifetime. When a thread need to
+ * add Landlock programs and if @usage is greater than 1, then the
+ * thread must duplicate struct landlock_hooks to not change the
+ * children' rules as well.
+ */
+struct landlock_hooks {
+ atomic_t usage;
+ struct landlock_rule *rules[_LANDLOCK_HOOK_LAST];
+};
+
+
+struct landlock_hooks *new_landlock_hooks(void);
+void put_landlock_hooks(struct landlock_hooks *hooks);
+
+#ifdef CONFIG_SECCOMP_FILTER
+void put_landlock_ret(struct landlock_seccomp_ret *landlock_ret);
+int landlock_seccomp_set_hook(unsigned int flags,
+ const char __user *user_bpf_fd);
+#endif /* CONFIG_SECCOMP_FILTER */
+
+#endif /* CONFIG_SECURITY_LANDLOCK */
+#endif /* _LINUX_LANDLOCK_H */
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index ffdab7cdd162..3cb90bf43a24 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -10,6 +10,10 @@
#include <linux/thread_info.h>
#include <asm/seccomp.h>

+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_SECURITY_LANDLOCK)
+#include <linux/landlock.h>
+#endif /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */
+
/**
* struct seccomp_filter - container for seccomp BPF programs
*
@@ -19,6 +23,7 @@
* is only needed for handling filters shared across tasks.
* @prev: points to a previously installed, or inherited, filter
* @prog: the BPF program to evaluate
+ * @thread_prev: points to filters installed by the same thread
*
* seccomp_filter objects are organized in a tree linked via the @prev
* pointer. For any task, it appears to be a singly-linked list starting
@@ -34,6 +39,9 @@ struct seccomp_filter {
atomic_t usage;
struct seccomp_filter *prev;
struct bpf_prog *prog;
+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_SECURITY_LANDLOCK)
+ struct seccomp_filter *thread_prev;
+#endif /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */
};

/**
@@ -43,6 +51,11 @@ struct seccomp_filter {
* system calls available to a process.
* @filter: must always point to a valid seccomp-filter or NULL as it is
* accessed without locking during system call entry.
+ * @thread_filter: list of filters allowed to trigger an associated Landlock
+ * hook via a RET_LANDLOCK; must walk through thread_prev.
+ * @landlock_ret: one unique private list per thread storing the RET_LANDLOCK
+ * values of all filters.
+ * @landlock_hooks: contains an array of Landlock programs.
*
* @filter must only be accessed from the context of current as there
* is no read locking.
@@ -50,6 +63,12 @@ struct seccomp_filter {
struct seccomp {
int mode;
struct seccomp_filter *filter;
+
+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_SECURITY_LANDLOCK)
+ struct seccomp_filter *thread_filter;
+ struct landlock_seccomp_ret *landlock_ret;
+ struct landlock_hooks *landlock_hooks;
+#endif /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */
};

#ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
@@ -103,13 +122,20 @@ static inline int seccomp_mode(struct seccomp *s)

#ifdef CONFIG_SECCOMP_FILTER
extern void put_seccomp(struct task_struct *tsk);
+extern void put_seccomp_filter(struct seccomp_filter *filter);
extern void get_seccomp_filter(struct task_struct *tsk);
+
#else /* CONFIG_SECCOMP_FILTER */
static inline void put_seccomp(struct task_struct *tsk)
{
return;
}

+static void put_seccomp_filter(struct seccomp_filter *filter)
+{
+ return;
+}
+
static inline void get_seccomp_filter(struct task_struct *tsk)
{
return;
diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index 0f238a43ff1e..a1273ceb5b3d 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h
@@ -13,6 +13,7 @@
/* Valid operations for seccomp syscall. */
#define SECCOMP_SET_MODE_STRICT 0
#define SECCOMP_SET_MODE_FILTER 1
+#define SECCOMP_SET_LANDLOCK_HOOK 2

/* Valid flags for SECCOMP_SET_MODE_FILTER */
#define SECCOMP_FILTER_FLAG_TSYNC 1
@@ -28,6 +29,7 @@
#define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */
#define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
#define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
+#define SECCOMP_RET_LANDLOCK 0x00070000U /* trigger Landlock LSM */
#define SECCOMP_RET_TRACE 0x7ff00000U /* pass to a tracer or disallow */
#define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */

diff --git a/kernel/fork.c b/kernel/fork.c
index 99df46f157cf..3dba89fa2cea 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -429,7 +429,12 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
* the usage counts on the error path calling free_task.
*/
tsk->seccomp.filter = NULL;
-#endif
+#ifdef CONFIG_SECURITY_LANDLOCK
+ tsk->seccomp.thread_filter = NULL;
+ tsk->seccomp.landlock_ret = NULL;
+ tsk->seccomp.landlock_hooks = NULL;
+#endif /* CONFIG_SECURITY_LANDLOCK */
+#endif /* CONFIG_SECCOMP */

setup_thread_stack(tsk, orig);
clear_user_return_notifier(tsk);
@@ -1284,7 +1289,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
return 0;
}

-static void copy_seccomp(struct task_struct *p)
+static int copy_seccomp(struct task_struct *p)
{
#ifdef CONFIG_SECCOMP
/*
@@ -1297,7 +1302,14 @@ static void copy_seccomp(struct task_struct *p)

/* Ref-count the new filter user, and assign it. */
get_seccomp_filter(current);
- p->seccomp = current->seccomp;
+ p->seccomp.mode = current->seccomp.mode;
+ p->seccomp.filter = current->seccomp.filter;
+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_SECURITY_LANDLOCK)
+ /* No copy for thread_filter nor landlock_ret. */
+ p->seccomp.landlock_hooks = current->seccomp.landlock_hooks;
+ if (p->seccomp.landlock_hooks)
+ atomic_inc(&p->seccomp.landlock_hooks->usage);
+#endif /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */

/*
* Explicitly enable no_new_privs here in case it got set
@@ -1315,6 +1327,7 @@ static void copy_seccomp(struct task_struct *p)
if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
set_tsk_thread_flag(p, TIF_SECCOMP);
#endif
+ return 0;
}

SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
@@ -1674,7 +1687,9 @@ static __latent_entropy struct task_struct *copy_process(
* Copy seccomp details explicitly here, in case they were changed
* before holding sighand lock.
*/
- copy_seccomp(p);
+ retval = copy_seccomp(p);
+ if (retval)
+ goto bad_fork_cancel_cgroup;

/*
* Process group and session signals need to be delivered to just the
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 92b15083b1b2..13729b8b9f21 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -6,6 +6,8 @@
* Copyright (C) 2012 Google, Inc.
* Will Drewry <wad@chromium.org>
*
+ * Copyright (C) 2016 Mickaël Salaün <mic@digikod.net>
+ *
* This defines a simple but solid secure-computing facility.
*
* Mode 1 uses a fixed list of allowed system calls.
@@ -32,12 +34,11 @@
#include <linux/security.h>
#include <linux/tracehook.h>
#include <linux/uaccess.h>
+#include <linux/landlock.h>

/* Limit any path through the tree to 256KB worth of instructions. */
#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))

-static void put_seccomp_filter(struct seccomp_filter *filter);
-
/*
* Endianness is explicitly ignored and left for BPF program authors to manage
* as per the specific architecture.
@@ -152,6 +153,10 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd)
{
struct seccomp_data sd_local;
u32 ret = SECCOMP_RET_ALLOW;
+#ifdef CONFIG_SECURITY_LANDLOCK
+ struct landlock_seccomp_ret *landlock_ret, *init_landlock_ret =
+ current->seccomp.landlock_ret;
+#endif /* CONFIG_SECURITY_LANDLOCK */
/* Make sure cross-thread synced filter points somewhere sane. */
struct seccomp_filter *f =
lockless_dereference(current->seccomp.filter);
@@ -171,8 +176,46 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd)
*/
for (; f; f = f->prev) {
u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd);
+ u32 action = cur_ret & SECCOMP_RET_ACTION;
+#ifdef CONFIG_SECURITY_LANDLOCK
+ u32 data = cur_ret & SECCOMP_RET_DATA;
+
+ if (action == SECCOMP_RET_LANDLOCK &&
+ current->seccomp.landlock_hooks) {
+ bool found_ret = false;
+
+ /*
+ * Keep track of filters from the current task that
+ * trigger a RET_LANDLOCK.
+ */
+ for (landlock_ret = init_landlock_ret;
+ landlock_ret;
+ landlock_ret = landlock_ret->prev) {
+ if (landlock_ret->filter == f) {
+ landlock_ret->triggered = true;
+ landlock_ret->cookie = data;
+ found_ret = true;
+ break;
+ }
+ }
+ if (!found_ret) {
+ /*
+ * Lazy allocation of landlock_ret; it will be
+ * freed when the thread will exit.
+ */
+ landlock_ret = kzalloc(sizeof(*landlock_ret),
+ GFP_KERNEL);
+ if (!landlock_ret)
+ return SECCOMP_RET_KILL;
+ atomic_inc(&f->usage);
+ landlock_ret->filter = f;
+ landlock_ret->prev = current->seccomp.landlock_ret;
+ current->seccomp.landlock_ret = landlock_ret;
+ }
+ }
+#endif /* CONFIG_SECURITY_LANDLOCK */

- if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
+ if (action < (ret & SECCOMP_RET_ACTION))
ret = cur_ret;
}
return ret;
@@ -424,6 +467,11 @@ static long seccomp_attach_filter(unsigned int flags,
*/
filter->prev = current->seccomp.filter;
current->seccomp.filter = filter;
+#ifdef CONFIG_SECURITY_LANDLOCK
+ /* Chain the filters from the same thread, if any. */
+ filter->thread_prev = current->seccomp.thread_filter;
+ current->seccomp.thread_filter = filter;
+#endif /* CONFIG_SECURITY_LANDLOCK */

/* Now that the new filter is in place, synchronize to all threads. */
if (flags & SECCOMP_FILTER_FLAG_TSYNC)
@@ -451,14 +499,16 @@ static inline void seccomp_filter_free(struct seccomp_filter *filter)
}

/* put_seccomp_filter - decrements the ref count of a filter */
-static void put_seccomp_filter(struct seccomp_filter *filter)
+void put_seccomp_filter(struct seccomp_filter *filter)
{
struct seccomp_filter *orig = filter;

/* Clean up single-reference branches iteratively. */
while (orig && atomic_dec_and_test(&orig->usage)) {
struct seccomp_filter *freeme = orig;
+
orig = orig->prev;
+ /* must not put orig->thread_prev */
seccomp_filter_free(freeme);
}
}
@@ -466,6 +516,10 @@ static void put_seccomp_filter(struct seccomp_filter *filter)
void put_seccomp(struct task_struct *tsk)
{
put_seccomp_filter(tsk->seccomp.filter);
+#ifdef CONFIG_SECURITY_LANDLOCK
+ put_landlock_hooks(tsk->seccomp.landlock_hooks);
+ put_landlock_ret(tsk->seccomp.landlock_ret);
+#endif /* CONFIG_SECURITY_LANDLOCK */
}

/**
@@ -612,6 +666,8 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,

return 0;

+ case SECCOMP_RET_LANDLOCK:
+ /* fall through */
case SECCOMP_RET_ALLOW:
return 0;

@@ -770,6 +826,10 @@ static long do_seccomp(unsigned int op, unsigned int flags,
return seccomp_set_mode_strict();
case SECCOMP_SET_MODE_FILTER:
return seccomp_set_mode_filter(flags, uargs);
+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_SECURITY_LANDLOCK)
+ case SECCOMP_SET_LANDLOCK_HOOK:
+ return landlock_seccomp_set_hook(flags, uargs);
+#endif /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */
default:
return -EINVAL;
}
diff --git a/security/landlock/Makefile b/security/landlock/Makefile
index 27f359a8cfaa..432c83e7c6b9 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -1,3 +1,3 @@
obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o

-landlock-y := lsm.o checker_fs.o
+landlock-y := lsm.o manager.o checker_fs.o
diff --git a/security/landlock/common.h b/security/landlock/common.h
new file mode 100644
index 000000000000..4e686b40c87f
--- /dev/null
+++ b/security/landlock/common.h
@@ -0,0 +1,27 @@
+/*
+ * Landlock LSM - private headers
+ *
+ * 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_COMMON_H
+#define _SECURITY_LANDLOCK_COMMON_H
+
+#include <linux/bpf.h> /* enum landlock_hook_id */
+
+/**
+ * get_index - get an index for the rules of struct landlock_hooks
+ *
+ * @hook_id: a Landlock hook ID
+ */
+static inline int get_index(enum landlock_hook_id hook_id)
+{
+ /* hook ID > 0 for loaded programs */
+ return hook_id - 1;
+}
+
+#endif /* _SECURITY_LANDLOCK_COMMON_H */
diff --git a/security/landlock/lsm.c b/security/landlock/lsm.c
index 952b7bc66328..b6e0bace683d 100644
--- a/security/landlock/lsm.c
+++ b/security/landlock/lsm.c
@@ -14,10 +14,13 @@
#include <linux/err.h> /* MAX_ERRNO */
#include <linux/filter.h> /* struct bpf_prog, BPF_PROG_RUN() */
#include <linux/kernel.h> /* FIELD_SIZEOF() */
+#include <linux/landlock.h>
#include <linux/lsm_hooks.h>
+#include <linux/seccomp.h> /* struct seccomp_* */
#include <linux/types.h> /* uintptr_t */

#include "checker_fs.h"
+#include "common.h"

#define LANDLOCK_MAP0(m, ...)
#define LANDLOCK_MAP1(m, d, t, a) m(d, t, a)
@@ -62,10 +65,99 @@

#define LANDLOCK_HOOK_INIT(NAME) LSM_HOOK_INIT(NAME, landlock_hook_##NAME)

+/**
+ * landlock_run_prog_for_syscall - run Landlock program for a syscall
+ *
+ * @hook_idx: hook index in the rules array
+ * @ctx: non-NULL eBPF context; the "origin" field will be updated
+ * @hooks: Landlock hooks pointer
+ */
+static u32 landlock_run_prog_for_syscall(u32 hook_idx,
+ struct landlock_data *ctx, struct landlock_hooks *hooks)
+{
+ struct landlock_rule *rule;
+ u32 cur_ret = 0, ret = 0;
+
+ if (!hooks)
+ return 0;
+
+ for (rule = hooks->rules[hook_idx]; rule && !ret; rule = rule->prev) {
+ if (!(rule->prog->subtype.landlock_hook.origin & ctx->origin))
+ continue;
+ cur_ret = BPF_PROG_RUN(rule->prog, (void *)ctx);
+ if (cur_ret > MAX_ERRNO)
+ ret = MAX_ERRNO;
+ else
+ ret = cur_ret;
+ }
+ return ret;
+}

static int landlock_run_prog(enum landlock_hook_id hook_id, __u64 args[6])
{
- return 0;
+ u32 cur_ret = 0, ret = 0;
+#ifdef CONFIG_SECCOMP_FILTER
+ struct landlock_seccomp_ret *lr;
+#endif /* CONFIG_SECCOMP_FILTER */
+ struct landlock_rule *rule;
+ u32 hook_idx = get_index(hook_id);
+
+ struct landlock_data ctx = {
+ .hook = hook_id,
+ .cookie = 0,
+ .args[0] = args[0],
+ .args[1] = args[1],
+ .args[2] = args[2],
+ .args[3] = args[3],
+ .args[4] = args[4],
+ .args[5] = args[5],
+ };
+
+ /* TODO: use lockless_dereference()? */
+
+#ifdef CONFIG_SECCOMP_FILTER
+ /* seccomp triggers and landlock_ret cleanup */
+ ctx.origin = LANDLOCK_FLAG_ORIGIN_SECCOMP;
+ for (lr = current->seccomp.landlock_ret; lr; lr = lr->prev) {
+ if (!lr->triggered)
+ continue;
+ lr->triggered = false;
+ /* clean up all seccomp results */
+ if (ret)
+ continue;
+ ctx.cookie = lr->cookie;
+ for (rule = current->seccomp.landlock_hooks->rules[hook_idx];
+ rule && !ret; rule = rule->prev) {
+ struct seccomp_filter *filter;
+
+ if (!(rule->prog->subtype.landlock_hook.origin &
+ ctx.origin))
+ continue;
+ for (filter = rule->thread_filter; filter;
+ filter = filter->thread_prev) {
+ if (rule->thread_filter != lr->filter)
+ continue;
+ cur_ret = BPF_PROG_RUN(rule->prog, (void *)&ctx);
+ if (cur_ret > MAX_ERRNO)
+ ret = MAX_ERRNO;
+ else
+ ret = cur_ret;
+ /* walk to the next program */
+ break;
+ }
+ }
+ }
+ if (ret)
+ return -ret;
+ ctx.cookie = 0;
+
+ /* syscall trigger */
+ ctx.origin = LANDLOCK_FLAG_ORIGIN_SYSCALL;
+ ret = landlock_run_prog_for_syscall(hook_idx, &ctx,
+ current->seccomp.landlock_hooks);
+#endif /* CONFIG_SECCOMP_FILTER */
+
+ return -ret;
}

static const struct bpf_func_proto *bpf_landlock_func_proto(
@@ -152,7 +244,7 @@ static struct security_hook_list landlock_hooks[] = {

void __init landlock_add_hooks(void)
{
- pr_info("landlock: Becoming ready for sandboxing\n");
+ pr_info("landlock: Becoming ready to sandbox with seccomp\n");
security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks));
}

diff --git a/security/landlock/manager.c b/security/landlock/manager.c
new file mode 100644
index 000000000000..e9f3f1092023
--- /dev/null
+++ b/security/landlock/manager.c
@@ -0,0 +1,242 @@
+/*
+ * Landlock LSM - seccomp and cgroups managers
+ *
+ * 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 <asm/atomic.h> /* atomic_*() */
+#include <asm/page.h> /* PAGE_SIZE */
+#include <asm/uaccess.h> /* copy_from_user() */
+#include <linux/bpf.h> /* bpf_prog_put() */
+#include <linux/filter.h> /* struct bpf_prog */
+#include <linux/kernel.h> /* round_up() */
+#include <linux/landlock.h>
+#include <linux/sched.h> /* current_cred(), task_no_new_privs() */
+#include <linux/security.h> /* security_capable_noaudit() */
+#include <linux/slab.h> /* alloc(), kfree() */
+#include <linux/types.h> /* atomic_t */
+
+#ifdef CONFIG_SECCOMP_FILTER
+#include <linux/seccomp.h> /* struct seccomp_filter */
+#endif /* CONFIG_SECCOMP_FILTER */
+
+#include "common.h"
+
+static void put_landlock_rule(struct landlock_rule *rule)
+{
+ struct landlock_rule *orig = rule;
+
+ /* Clean up single-reference branches iteratively. */
+ while (orig && atomic_dec_and_test(&orig->usage)) {
+ struct landlock_rule *freeme = orig;
+
+#ifdef CONFIG_SECCOMP_FILTER
+ put_seccomp_filter(orig->thread_filter);
+#endif /* CONFIG_SECCOMP_FILTER */
+ bpf_prog_put(orig->prog);
+ orig = orig->prev;
+ kfree(freeme);
+ }
+}
+
+void put_landlock_hooks(struct landlock_hooks *hooks)
+{
+ if (!hooks)
+ return;
+
+ if (atomic_dec_and_test(&hooks->usage)) {
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(hooks->rules); i++)
+ put_landlock_rule(hooks->rules[i]);
+ kfree(hooks);
+ }
+}
+
+#ifdef CONFIG_SECCOMP_FILTER
+void put_landlock_ret(struct landlock_seccomp_ret *landlock_ret)
+{
+ struct landlock_seccomp_ret *orig = landlock_ret;
+
+ while (orig) {
+ struct landlock_seccomp_ret *freeme = orig;
+
+ put_seccomp_filter(orig->filter);
+ orig = orig->prev;
+ kfree(freeme);
+ }
+}
+#endif /* CONFIG_SECCOMP_FILTER */
+
+struct landlock_hooks *new_landlock_hooks(void)
+{
+ struct landlock_hooks *ret;
+
+ /* array filled with NULL values */
+ ret = kzalloc(sizeof(*ret), GFP_KERNEL);
+ if (!ret)
+ return ERR_PTR(-ENOMEM);
+ atomic_set(&ret->usage, 1);
+ return ret;
+}
+
+/* Limit Landlock hooks to 256KB. */
+#define LANDLOCK_HOOKS_MAX_PAGES (1 << 6)
+
+/**
+ * landlock_set_hook - attach a Landlock program to @current_hooks
+ *
+ * @current_hooks: landlock_hooks pointer, must be locked (if needed) to
+ * prevent a concurrent put/free. This pointer must not be
+ * freed after the call.
+ * @prog: non-NULL Landlock program to append to @current_hooks. @prog will be
+ * owned by landlock_set_hook() and freed if an error happened.
+ * @thread_filter: pointer to the seccomp filter of the current thread, if any
+ *
+ * Return @current_hooks or a new pointer when OK. Return a pointer error
+ * otherwise.
+ */
+static struct landlock_hooks *landlock_set_hook(
+ struct landlock_hooks *current_hooks, struct bpf_prog *prog,
+ struct seccomp_filter *thread_filter)
+{
+ struct landlock_hooks *new_hooks = current_hooks;
+ unsigned long pages;
+ struct landlock_rule *rule;
+ u32 hook_idx;
+
+ if (prog->type != BPF_PROG_TYPE_LANDLOCK) {
+ new_hooks = ERR_PTR(-EINVAL);
+ goto put_prog;
+ }
+
+ /* validate allocated memory */
+ pages = prog->pages;
+ if (current_hooks) {
+ int i;
+ struct landlock_rule *walker;
+
+ for (i = 0; i < ARRAY_SIZE(current_hooks->rules); i++) {
+ for (walker = current_hooks->rules[i]; walker;
+ walker = walker->prev) {
+ /* TODO: add penalty for each prog? */
+ pages += walker->prog->pages;
+ }
+ }
+ /* count landlock_hooks if we will allocate it */
+ if (atomic_read(&current_hooks->usage) != 1)
+ pages += round_up(sizeof(*current_hooks), PAGE_SIZE) /
+ PAGE_SIZE;
+ }
+ if (pages > LANDLOCK_HOOKS_MAX_PAGES) {
+ new_hooks = ERR_PTR(-E2BIG);
+ goto put_prog;
+ }
+
+ rule = kmalloc(sizeof(*rule), GFP_KERNEL);
+ if (!rule) {
+ new_hooks = ERR_PTR(-ENOMEM);
+ goto put_prog;
+ }
+ rule->prev = NULL;
+ rule->prog = prog;
+ /* attach the filters from the same thread, if any */
+ rule->thread_filter = thread_filter;
+ if (rule->thread_filter)
+ atomic_inc(&rule->thread_filter->usage);
+ atomic_set(&rule->usage, 1);
+
+ if (!current_hooks) {
+ /* add a new landlock_hooks, if needed */
+ new_hooks = new_landlock_hooks();
+ if (IS_ERR(new_hooks))
+ goto put_rule;
+ } else if (atomic_read(&current_hooks->usage) > 1) {
+ int i;
+
+ /* copy landlock_hooks, if shared */
+ new_hooks = new_landlock_hooks();
+ if (IS_ERR(new_hooks))
+ goto put_rule;
+ for (i = 0; i < ARRAY_SIZE(new_hooks->rules); i++) {
+ new_hooks->rules[i] =
+ current_hooks->rules[i];
+ if (new_hooks->rules[i])
+ atomic_inc(&new_hooks->rules[i]->usage);
+ }
+ /*
+ * @current_hooks will not be freed here because it's usage
+ * field is > 1. It is only prevented to be freed by another
+ * subject thanks to the caller of landlock_set_hook() which
+ * should be locked if needed.
+ */
+ put_landlock_hooks(current_hooks);
+ }
+
+ /* subtype.landlock_hook.id > 0 for loaded programs */
+ hook_idx = get_index(rule->prog->subtype.landlock_hook.id);
+ rule->prev = new_hooks->rules[hook_idx];
+ new_hooks->rules[hook_idx] = rule;
+ return new_hooks;
+
+put_prog:
+ bpf_prog_put(prog);
+ return new_hooks;
+
+put_rule:
+ put_landlock_rule(rule);
+ return new_hooks;
+}
+
+/**
+ * landlock_set_hook - attach a Landlock program to the current process
+ *
+ * current->seccomp.landlock_hooks is lazily allocated. When a process fork,
+ * only a pointer is copied. When a new hook is added by a process, if there is
+ * other references to this process' landlock_hooks, then a new allocation is
+ * made to contains an array pointing to Landlock program lists. This design
+ * has low-performance impact and memory efficiency while keeping the property
+ * of append-only programs.
+ *
+ * @flags: not used for now, but could be used for TSYNC
+ * @user_bpf_fd: file descriptor pointing to a loaded/checked eBPF program
+ * dedicated to Landlock
+ */
+#ifdef CONFIG_SECCOMP_FILTER
+int landlock_seccomp_set_hook(unsigned int flags, const char __user *user_bpf_fd)
+{
+ struct landlock_hooks *new_hooks;
+ struct bpf_prog *prog;
+ int bpf_fd;
+
+ if (!task_no_new_privs(current) &&
+ security_capable_noaudit(current_cred(),
+ current_user_ns(), CAP_SYS_ADMIN) != 0)
+ return -EPERM;
+ if (!user_bpf_fd)
+ return -EINVAL;
+ if (flags)
+ return -EINVAL;
+ if (copy_from_user(&bpf_fd, user_bpf_fd, sizeof(user_bpf_fd)))
+ return -EFAULT;
+ prog = bpf_prog_get(bpf_fd);
+ if (IS_ERR(prog))
+ return PTR_ERR(prog);
+
+ /*
+ * We don't need to lock anything for the current process hierarchy,
+ * everything is guarded by the atomic counters.
+ */
+ new_hooks = landlock_set_hook(current->seccomp.landlock_hooks, prog,
+ current->seccomp.thread_filter);
+ /* @prog is managed/freed by landlock_set_hook() */
+ if (IS_ERR(new_hooks))
+ return PTR_ERR(new_hooks);
+ current->seccomp.landlock_hooks = new_hooks;
+ return 0;
+}
+#endif /* CONFIG_SECCOMP_FILTER */
--
2.9.3
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