[PATCH bpf-next v9 04/10] seccomp,landlock: Enforce Landlock programs per process hierarchy

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Landlock LSM - public kernel headers
+ *
+ * Copyright © 2016-2019 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2019 ANSSI
+ */
+
+#ifndef _LINUX_LANDLOCK_H
+#define _LINUX_LANDLOCK_H
+
+#include <linux/errno.h>
+#include <linux/sched.h> /* task_struct */
+
+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_SECURITY_LANDLOCK)
+extern int landlock_seccomp_prepend_prog(unsigned int flags,
+		const int __user *user_bpf_fd);
+extern void put_seccomp_landlock(struct task_struct *tsk);
+extern void get_seccomp_landlock(struct task_struct *tsk);
+#else /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */
+static inline int landlock_seccomp_prepend_prog(unsigned int flags,
+		const int __user *user_bpf_fd)
+{
+		return -EINVAL;
+}
+static inline void put_seccomp_landlock(struct task_struct *tsk)
+{
+}
+static inline void get_seccomp_landlock(struct task_struct *tsk)
+{
+}
+#endif /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */
+
+#endif /* _LINUX_LANDLOCK_H */

@@ -11,6 +11,7 @@
 
 #ifdef CONFIG_SECCOMP
 
+#include <linux/landlock.h>
 #include <linux/thread_info.h>
 #include <asm/seccomp.h>
 

@@ -22,6 +23,7 @@ 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.
+ * @landlock_prog_set: contains a set of Landlock programs.
  *
  *          @filter must only be accessed from the context of current as there
  *          is no read locking.

@@ -29,6 +31,9 @@ struct seccomp_filter;
 struct seccomp {
 	int mode;
 	struct seccomp_filter *filter;
+#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_SECURITY_LANDLOCK)
+	struct landlock_prog_set *landlock_prog_set;
+#endif /* CONFIG_SECCOMP_FILTER && CONFIG_SECURITY_LANDLOCK */
 };
 
 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER

@@ -16,6 +16,7 @@
 #define SECCOMP_SET_MODE_FILTER		1
 #define SECCOMP_GET_ACTION_AVAIL	2
 #define SECCOMP_GET_NOTIF_SIZES		3
+#define SECCOMP_PREPEND_LANDLOCK_PROG	4
 
 /* Valid flags for SECCOMP_SET_MODE_FILTER */
 #define SECCOMP_FILTER_FLAG_TSYNC		(1UL << 0)

@@ -51,6 +51,7 @@
 #include <linux/security.h>
 #include <linux/hugetlb.h>
 #include <linux/seccomp.h>
+#include <linux/landlock.h>
 #include <linux/swap.h>
 #include <linux/syscalls.h>
 #include <linux/jiffies.h>

@@ -454,6 +455,7 @@ void free_task(struct task_struct *tsk)
 	rt_mutex_debug_task_free(tsk);
 	ftrace_graph_exit_task(tsk);
 	put_seccomp_filter(tsk);
+	put_seccomp_landlock(tsk);
 	arch_release_task_struct(tsk);
 	if (tsk->flags & PF_KTHREAD)
 		free_kthread_struct(tsk);

@@ -884,7 +886,10 @@ 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.landlock_prog_set = NULL;
+#endif /* CONFIG_SECURITY_LANDLOCK */
+#endif /* CONFIG_SECCOMP */
 
 	setup_thread_stack(tsk, orig);
 	clear_user_return_notifier(tsk);

@@ -1598,6 +1603,7 @@ static void copy_seccomp(struct task_struct *p)
 
 	/* Ref-count the new filter user, and assign it. */
 	get_seccomp_filter(current);
+	get_seccomp_landlock(current);
 	p->seccomp = current->seccomp;
 
 	/*

@@ -41,6 +41,7 @@
 #include <linux/tracehook.h>
 #include <linux/uaccess.h>
 #include <linux/anon_inodes.h>
+#include <linux/landlock.h>
 
 enum notify_state {
 	SECCOMP_NOTIFY_INIT,

@@ -1397,6 +1398,9 @@ static long do_seccomp(unsigned int op, unsigned int flags,
 			return -EINVAL;
 
 		return seccomp_get_notif_sizes(uargs);
+	case SECCOMP_PREPEND_LANDLOCK_PROG:
+		return landlock_seccomp_prepend_prog(flags,
+				(const int __user *)uargs);
 	default:
 		return -EINVAL;
 	}

@@ -1,3 +1,4 @@
 obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
 
-landlock-y := init.o
+landlock-y := init.o \
+	enforce.o enforce_seccomp.o

@@ -23,4 +23,49 @@
 #define _LANDLOCK_TRIGGER_FS_PICK_LAST	LANDLOCK_TRIGGER_FS_PICK_WRITE
 #define _LANDLOCK_TRIGGER_FS_PICK_MASK	((_LANDLOCK_TRIGGER_FS_PICK_LAST << 1ULL) - 1)
 
+extern struct lsm_blob_sizes landlock_blob_sizes;
+
+struct landlock_prog_list {
+	struct landlock_prog_list *prev;
+	struct bpf_prog *prog;
+	refcount_t usage;
+};
+
+/**
+ * struct landlock_prog_set - Landlock 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 of each entries, only
+ * create a pointer to &struct landlock_prog_set and increments its usage. When
+ * prepending a new program, if &struct landlock_prog_set is shared with other
+ * tasks, then duplicate it and prepend the program to this new &struct
+ * landlock_prog_set.
+ *
+ * @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_prog_set to not change the
+ *	   children's programs as well.
+ * @programs: array of non-NULL &struct landlock_prog_list pointers
+ */
+struct landlock_prog_set {
+	struct landlock_prog_list *programs[_LANDLOCK_HOOK_LAST];
+	refcount_t usage;
+};
+
+/**
+ * get_index - get an index for the programs of struct landlock_prog_set
+ *
+ * @type: a Landlock hook type
+ */
+static inline int get_index(enum landlock_hook_type type)
+{
+	/* type ID > 0 for loaded programs */
+	return type - 1;
+}
+
+static inline enum landlock_hook_type get_type(struct bpf_prog *prog)
+{
+	return prog->aux->extra->subtype.landlock_hook.type;
+}
+
 #endif /* _SECURITY_LANDLOCK_COMMON_H */

@@ -0,0 +1,272 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - enforcing helpers
+ *
+ * Copyright © 2016-2019 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2019 ANSSI
+ */
+
+#include <asm/barrier.h> /* smp_store_release() */
+#include <asm/page.h> /* PAGE_SIZE */
+#include <linux/bpf.h> /* bpf_prog_put() */
+#include <linux/compiler.h> /* READ_ONCE() */
+#include <linux/err.h> /* PTR_ERR() */
+#include <linux/errno.h>
+#include <linux/filter.h> /* struct bpf_prog */
+#include <linux/refcount.h>
+#include <linux/slab.h> /* alloc(), kfree() */
+
+#include "common.h" /* struct landlock_prog_list */
+
+/* TODO: use a dedicated kmem_cache_alloc() instead of k*alloc() */
+
+static void put_landlock_prog_list(struct landlock_prog_list *prog_list)
+{
+	struct landlock_prog_list *orig = prog_list;
+
+	/* clean up single-reference branches iteratively */
+	while (orig && refcount_dec_and_test(&orig->usage)) {
+		struct landlock_prog_list *freeme = orig;
+
+		if (orig->prog)
+			bpf_prog_put(orig->prog);
+		orig = orig->prev;
+		kfree(freeme);
+	}
+}
+
+void landlock_put_prog_set(struct landlock_prog_set *prog_set)
+{
+	if (prog_set && refcount_dec_and_test(&prog_set->usage)) {
+		size_t i;
+
+		for (i = 0; i < ARRAY_SIZE(prog_set->programs); i++)
+			put_landlock_prog_list(prog_set->programs[i]);
+		kfree(prog_set);
+	}
+}
+
+void landlock_get_prog_set(struct landlock_prog_set *prog_set)
+{
+	if (!prog_set)
+		return;
+	refcount_inc(&prog_set->usage);
+}
+
+static struct landlock_prog_set *new_landlock_prog_set(void)
+{
+	struct landlock_prog_set *ret;
+
+	/* array filled with NULL values */
+	ret = kzalloc(sizeof(*ret), GFP_KERNEL);
+	if (!ret)
+		return ERR_PTR(-ENOMEM);
+	refcount_set(&ret->usage, 1);
+	return ret;
+}
+
+/**
+ * store_landlock_prog - prepend and deduplicate a Landlock prog_list
+ *
+ * Prepend @prog to @init_prog_set while ignoring @prog
+ * if they are already in @ref_prog_set.  Whatever is the result of this
+ * function call, you can call bpf_prog_put(@prog) after.
+ *
+ * @init_prog_set: empty prog_set to prepend to
+ * @ref_prog_set: prog_set to check for duplicate programs
+ * @prog: program to prepend
+ *
+ * Return -errno on error or 0 if @prog was successfully stored.
+ */
+static int store_landlock_prog(struct landlock_prog_set *init_prog_set,
+		const struct landlock_prog_set *ref_prog_set,
+		struct bpf_prog *prog)
+{
+	struct landlock_prog_list *tmp_list = NULL;
+	int err;
+	u32 hook_idx;
+	enum landlock_hook_type last_type;
+	struct bpf_prog *new = prog;
+
+	/* allocate all the memory we need */
+	struct landlock_prog_list *new_list;
+
+	last_type = get_type(new);
+
+	/* ignore duplicate programs */
+	if (ref_prog_set) {
+		struct landlock_prog_list *ref;
+
+		hook_idx = get_index(get_type(new));
+		for (ref = ref_prog_set->programs[hook_idx];
+				ref; ref = ref->prev) {
+			if (ref->prog == new)
+				return -EINVAL;
+		}
+	}
+
+	new = bpf_prog_inc(new);
+	if (IS_ERR(new)) {
+		err = PTR_ERR(new);
+		goto put_tmp_list;
+	}
+	new_list = kzalloc(sizeof(*new_list), GFP_KERNEL);
+	if (!new_list) {
+		bpf_prog_put(new);
+		err = -ENOMEM;
+		goto put_tmp_list;
+	}
+	/* ignore Landlock types in this tmp_list */
+	new_list->prog = new;
+	new_list->prev = tmp_list;
+	refcount_set(&new_list->usage, 1);
+	tmp_list = new_list;
+
+	if (!tmp_list)
+		/* inform user space that this program was already added */
+		return -EEXIST;
+
+	/* properly store the list (without error cases) */
+	while (tmp_list) {
+		struct landlock_prog_list *new_list;
+
+		new_list = tmp_list;
+		tmp_list = tmp_list->prev;
+		/* do not increment the previous prog list usage */
+		hook_idx = get_index(get_type(new_list->prog));
+		new_list->prev = init_prog_set->programs[hook_idx];
+		/* no need to add from the last program to the first because
+		 * each of them are a different Landlock type */
+		smp_store_release(&init_prog_set->programs[hook_idx], new_list);
+	}
+	return 0;
+
+put_tmp_list:
+	put_landlock_prog_list(tmp_list);
+	return err;
+}
+
+/* limit Landlock programs set to 256KB */
+#define LANDLOCK_PROGRAMS_MAX_PAGES (1 << 6)
+
+/**
+ * landlock_prepend_prog - attach a Landlock prog_list to @current_prog_set
+ *
+ * Whatever is the result of this function call, you can call
+ * bpf_prog_put(@prog) after.
+ *
+ * @current_prog_set: landlock_prog_set 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 prog_list to prepend to @current_prog_set. @prog
+ *	  will be owned by landlock_prepend_prog() and freed if an error
+ *	  happened.
+ *
+ * Return @current_prog_set or a new pointer when OK. Return a pointer error
+ * otherwise.
+ */
+struct landlock_prog_set *landlock_prepend_prog(
+		struct landlock_prog_set *current_prog_set,
+		struct bpf_prog *prog)
+{
+	struct landlock_prog_set *new_prog_set = current_prog_set;
+	unsigned long pages;
+	int err;
+	size_t i;
+	struct landlock_prog_set tmp_prog_set = {};
+
+	if (prog->type != BPF_PROG_TYPE_LANDLOCK_HOOK)
+		return ERR_PTR(-EINVAL);
+
+	/* validate memory size allocation */
+	pages = prog->pages;
+	if (current_prog_set) {
+		size_t i;
+
+		for (i = 0; i < ARRAY_SIZE(current_prog_set->programs); i++) {
+			struct landlock_prog_list *walker_p;
+
+			for (walker_p = current_prog_set->programs[i];
+					walker_p; walker_p = walker_p->prev)
+				pages += walker_p->prog->pages;
+		}
+		/* count a struct landlock_prog_set if we need to allocate one */
+		if (refcount_read(&current_prog_set->usage) != 1)
+			pages += round_up(sizeof(*current_prog_set), PAGE_SIZE)
+				/ PAGE_SIZE;
+	}
+	if (pages > LANDLOCK_PROGRAMS_MAX_PAGES)
+		return ERR_PTR(-E2BIG);
+
+	/* ensure early that we can allocate enough memory for the new
+	 * prog_lists */
+	err = store_landlock_prog(&tmp_prog_set, current_prog_set, prog);
+	if (err)
+		return ERR_PTR(err);
+
+	/*
+	 * Each task_struct points to an array of prog list pointers.  These
+	 * tables are duplicated when additions are made (which means each
+	 * table needs to be refcounted for the processes using it). When a new
+	 * table is created, all the refcounters on the prog_list are bumped (to
+	 * track each table that references the prog). When a new prog is
+	 * added, it's just prepended to the list for the new table to point
+	 * at.
+	 *
+	 * Manage all the possible errors before this step to not uselessly
+	 * duplicate current_prog_set and avoid a rollback.
+	 */
+	if (!new_prog_set) {
+		/*
+		 * If there is no Landlock program set used by the current task,
+		 * then create a new one.
+		 */
+		new_prog_set = new_landlock_prog_set();
+		if (IS_ERR(new_prog_set))
+			goto put_tmp_lists;
+	} else if (refcount_read(&current_prog_set->usage) > 1) {
+		/*
+		 * If the current task is not the sole user of its Landlock
+		 * program set, then duplicate them.
+		 */
+		new_prog_set = new_landlock_prog_set();
+		if (IS_ERR(new_prog_set))
+			goto put_tmp_lists;
+		for (i = 0; i < ARRAY_SIZE(new_prog_set->programs); i++) {
+			new_prog_set->programs[i] =
+				READ_ONCE(current_prog_set->programs[i]);
+			if (new_prog_set->programs[i])
+				refcount_inc(&new_prog_set->programs[i]->usage);
+		}
+
+		/*
+		 * Landlock program set from the current task will not be freed
+		 * here because the usage is strictly greater than 1. It is
+		 * only prevented to be freed by another task thanks to the
+		 * caller of landlock_prepend_prog() which should be locked if
+		 * needed.
+		 */
+		landlock_put_prog_set(current_prog_set);
+	}
+
+	/* prepend tmp_prog_set to new_prog_set */
+	for (i = 0; i < ARRAY_SIZE(tmp_prog_set.programs); i++) {
+		/* get the last new list */
+		struct landlock_prog_list *last_list =
+			tmp_prog_set.programs[i];
+
+		if (last_list) {
+			while (last_list->prev)
+				last_list = last_list->prev;
+			/* no need to increment usage (pointer replacement) */
+			last_list->prev = new_prog_set->programs[i];
+			new_prog_set->programs[i] = tmp_prog_set.programs[i];
+		}
+	}
+	return new_prog_set;
+
+put_tmp_lists:
+	for (i = 0; i < ARRAY_SIZE(tmp_prog_set.programs); i++)
+		put_landlock_prog_list(tmp_prog_set.programs[i]);
+	return new_prog_set;
+}

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - enforcing helpers headers
+ *
+ * Copyright © 2016-2019 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2019 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_ENFORCE_H
+#define _SECURITY_LANDLOCK_ENFORCE_H
+
+struct landlock_prog_set *landlock_prepend_prog(
+		struct landlock_prog_set *current_prog_set,
+		struct bpf_prog *prog);
+void landlock_put_prog_set(struct landlock_prog_set *prog_set);
+void landlock_get_prog_set(struct landlock_prog_set *prog_set);
+
+#endif /* _SECURITY_LANDLOCK_ENFORCE_H */

@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - enforcing with seccomp
+ *
+ * Copyright © 2016-2018 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2019 ANSSI
+ */
+
+#ifdef CONFIG_SECCOMP_FILTER
+
+#include <linux/bpf.h> /* bpf_prog_put() */
+#include <linux/capability.h>
+#include <linux/err.h> /* PTR_ERR() */
+#include <linux/errno.h>
+#include <linux/filter.h> /* struct bpf_prog */
+#include <linux/landlock.h>
+#include <linux/refcount.h>
+#include <linux/sched.h> /* current */
+#include <linux/uaccess.h> /* get_user() */
+
+#include "enforce.h"
+
+/* headers in include/linux/landlock.h */
+
+/**
+ * landlock_seccomp_prepend_prog - attach a Landlock program to the current
+ *                                 process
+ *
+ * current->seccomp.landlock_state->prog_set is lazily allocated. When a
+ * process fork, only a pointer is copied.  When a new program is added by a
+ * process, if there is other references to this process' prog_set, then a new
+ * allocation is made to contain an array pointing to Landlock program lists.
+ * This design enable low-performance impact and is memory efficient while
+ * keeping the property of prepend-only programs.
+ *
+ * For now, installing a Landlock prog requires that the requesting task has
+ * the global CAP_SYS_ADMIN. We cannot force the use of no_new_privs to not
+ * exclude containers where a process may legitimately acquire more privileges
+ * thanks to an SUID binary.
+ *
+ * @flags: not used for now, but could be used for TSYNC
+ * @user_bpf_fd: file descriptor pointing to a loaded Landlock prog
+ */
+int landlock_seccomp_prepend_prog(unsigned int flags,
+		const int __user *user_bpf_fd)
+{
+	struct landlock_prog_set *new_prog_set;
+	struct bpf_prog *prog;
+	int bpf_fd, err;
+
+	/* planned to be replaced with a no_new_privs check to allow
+	 * unprivileged tasks */
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	/* enable to check if Landlock is supported with early EFAULT */
+	if (!user_bpf_fd)
+		return -EFAULT;
+	if (flags)
+		return -EINVAL;
+	err = get_user(bpf_fd, user_bpf_fd);
+	if (err)
+		return err;
+
+	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_prog_set = landlock_prepend_prog(
+			current->seccomp.landlock_prog_set, prog);
+	bpf_prog_put(prog);
+	/* @prog is managed/freed by landlock_prepend_prog() */
+	if (IS_ERR(new_prog_set))
+		return PTR_ERR(new_prog_set);
+	current->seccomp.landlock_prog_set = new_prog_set;
+	return 0;
+}
+
+void put_seccomp_landlock(struct task_struct *tsk)
+{
+	landlock_put_prog_set(tsk->seccomp.landlock_prog_set);
+}
+
+void get_seccomp_landlock(struct task_struct *tsk)
+{
+	landlock_get_prog_set(tsk->seccomp.landlock_prog_set);
+}
+
+#endif /* CONFIG_SECCOMP_FILTER */