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Subject[PATCH v6 2/3] seccomp_filters: system call filtering using BPF
Date
[This patch depends on luto@mit.edu's no_new_privs patch:
https://lkml.org/lkml/2012/1/12/446
]

This patch adds support for seccomp mode 2. This mode enables dynamic
enforcement of system call filtering policy in the kernel as specified
by a userland task. The policy is expressed in terms of a Berkeley
Packet Filter program, as is used for userland-exposed socket filtering.
Instead of network data, the BPF program is evaluated over struct
seccomp_filter_data at the time of the system call.

A filter program may be installed by a userland task by calling
prctl(PR_ATTACH_SECCOMP_FILTER, &fprog);
where fprog is of type struct sock_fprog.

If the first filter program allows subsequent prctl(2) calls, then
additional filter programs may be attached. All attached programs
must be evaluated before a system call will be allowed to proceed.

To avoid CONFIG_COMPAT related landmines, once a filter program is
installed using specific is_compat_task() value, it is not allowed to
make system calls using the alternate entry point.

Filter programs will be inherited across fork/clone and execve, however
the installation of filters must be preceded by setting 'no_new_privs'
to ensure that unprivileged tasks cannot attach filters that affect
privileged tasks (e.g., setuid binary). Tasks with CAP_SYS_ADMIN
in their namespace may install inheritable filters without setting
the no_new_privs bit.

There are a number of benefits to this approach. A few of which are
as follows:
- BPF has been exposed to userland for a long time.
- Userland already knows its ABI: system call numbers and desired
arguments
- No time-of-check-time-of-use vulnerable data accesses are possible.
- system call arguments are loaded on demand only to minimize copying
required for system call number-only policy decisions.

This patch includes its own BPF evaluator, but relies on the
net/core/filter.c BPF checking code. It is possible to share
evaluators, but the performance sensitive nature of the network
filtering path makes it an iterative optimization which (I think :) can
be tackled separately via separate patchsets. (And at some point sharing
BPF JIT code!)

v6: - fix memory leak on attach compat check failure
- require no_new_privs || CAP_SYS_ADMIN prior to filter
installation. (luto@mit.edu)
- s/seccomp_struct_/seccomp_/ for macros/functions
(amwang@redhat.com)
- cleaned up Kconfig (amwang@redhat.com)
- on block, note if the call was compat (so the # means something)
v5: - uses syscall_get_arguments
(indan@nul.nu,oleg@redhat.com, mcgrathr@chromium.org)
- uses union-based arg storage with hi/lo struct to
handle endianness. Compromises between the two alternate
proposals to minimize extra arg shuffling and account for
endianness assuming userspace uses offsetof().
(mcgrathr@chromium.org, indan@nul.nu)
- update Kconfig description
- add include/seccomp_filter.h and add its installation
- (naive) on-demand syscall argument loading
- drop seccomp_t (eparis@redhat.com)
v4: - adjusted prctl to make room for PR_[SG]ET_NO_NEW_PRIVS
- now uses current->no_new_privs
(luto@mit.edu,torvalds@linux-foundation.com)
- assign names to seccomp modes (rdunlap@xenotime.net)
- fix style issues (rdunlap@xenotime.net)
- reworded Kconfig entry (rdunlap@xenotime.net)
v3: - macros to inline (oleg@redhat.com)
- init_task behavior fixed (oleg@redhat.com)
- drop creator entry and extra NULL check (oleg@redhat.com)
- alloc returns -EINVAL on bad sizing (serge.hallyn@canonical.com)
- adds tentative use of "always_unprivileged" as per
torvalds@linux-foundation.org and luto@mit.edu
v2: - (patch 2 only)
Signed-off-by: Will Drewry <wad@chromium.org>
---
include/linux/Kbuild | 1 +
include/linux/prctl.h | 3 +
include/linux/seccomp.h | 63 ++++
include/linux/seccomp_filter.h | 79 +++++
kernel/Makefile | 1 +
kernel/fork.c | 4 +
kernel/seccomp.c | 10 +-
kernel/seccomp_filter.c | 627 ++++++++++++++++++++++++++++++++++++++++
kernel/sys.c | 4 +
security/Kconfig | 20 ++
10 files changed, 811 insertions(+), 1 deletions(-)
create mode 100644 include/linux/seccomp_filter.h
create mode 100644 kernel/seccomp_filter.c
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index c94e717..5659454 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -330,6 +330,7 @@ header-y += scc.h
header-y += sched.h
header-y += screen_info.h
header-y += sdla.h
+header-y += seccomp_filter.h
header-y += securebits.h
header-y += selinux_netlink.h
header-y += sem.h
diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index 7ddc7f1..b8c4beb 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -114,4 +114,7 @@
# define PR_SET_MM_START_BRK 6
# define PR_SET_MM_BRK 7

+/* Set process seccomp filters */
+#define PR_ATTACH_SECCOMP_FILTER 37
+
#endif /* _LINUX_PRCTL_H */
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 171ab66..d3b896b 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -5,10 +5,29 @@
#ifdef CONFIG_SECCOMP

#include <linux/thread_info.h>
+#include <linux/types.h>
#include <asm/seccomp.h>

+/* Valid values of seccomp_struct.mode */
+#define SECCOMP_MODE_DISABLED 0 /* seccomp is not in use. */
+#define SECCOMP_MODE_STRICT 1 /* uses hard-coded seccomp.c rules. */
+#define SECCOMP_MODE_FILTER 2 /* system call access determined by filter. */
+
+struct seccomp_filter;
+/**
+ * struct seccomp_struct - the state of a seccomp'ed process
+ *
+ * @mode: indicates one of the valid values above for controlled
+ * system calls available to a process.
+ * @filter: Metadata for filter if using CONFIG_SECCOMP_FILTER.
+ * @filter must only be accessed from the context of current as there
+ * is no guard.
+ */
struct seccomp_struct {
int mode;
+#ifdef CONFIG_SECCOMP_FILTER
+ struct seccomp_filter *filter;
+#endif
};

extern void __secure_computing(int);
@@ -51,4 +70,48 @@ static inline int seccomp_mode(struct seccomp_struct *s)

#endif /* CONFIG_SECCOMP */

+#ifdef CONFIG_SECCOMP_FILTER
+
+
+extern long prctl_attach_seccomp_filter(char __user *);
+
+extern struct seccomp_filter *get_seccomp_filter(struct seccomp_filter *);
+extern void put_seccomp_filter(struct seccomp_filter *);
+
+extern int seccomp_test_filters(int);
+extern void seccomp_filter_log_failure(int);
+extern void seccomp_fork(struct seccomp_struct *child,
+ const struct seccomp_struct *parent);
+
+static inline void seccomp_init_task(struct seccomp_struct *seccomp)
+{
+ seccomp->mode = SECCOMP_MODE_DISABLED;
+ seccomp->filter = NULL;
+}
+
+/* No locking is needed here because the task_struct will
+ * have no parallel consumers.
+ */
+static inline void seccomp_free_task(struct seccomp_struct *seccomp)
+{
+ put_seccomp_filter(seccomp->filter);
+ seccomp->filter = NULL;
+}
+
+#else /* CONFIG_SECCOMP_FILTER */
+
+#include <linux/errno.h>
+
+struct seccomp_filter { };
+/* Macros consume the unused dereference by the caller. */
+#define seccomp_init_task(_seccomp) do { } while (0);
+#define seccomp_fork(_tsk, _orig) do { } while (0);
+#define seccomp_free_task(_seccomp) do { } while (0);
+
+static inline long prctl_attach_seccomp_filter(char __user *a2)
+{
+ return -ENOSYS;
+}
+
+#endif /* CONFIG_SECCOMP_FILTER */
#endif /* _LINUX_SECCOMP_H */
diff --git a/include/linux/seccomp_filter.h b/include/linux/seccomp_filter.h
new file mode 100644
index 0000000..3ecd641
--- /dev/null
+++ b/include/linux/seccomp_filter.h
@@ -0,0 +1,79 @@
+/*
+ * Secomp-based system call filtering data structures and definitions.
+ *
+ * Copyright (C) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ *
+ * This copyrighted material is made available to anyone wishing to use,
+ * modify, copy, or redistribute it subject to the terms and conditions
+ * of the GNU General Public License v.2.
+ *
+ */
+
+#ifndef __LINUX_SECCOMP_FILTER_H__
+#define __LINUX_SECCOMP_FILTER_H__
+
+#include <asm/byteorder.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+/*
+ * Keep the contents of this file similar to linux/filter.h:
+ * struct sock_filter and sock_fprog and versions.
+ * Custom naming exists solely if divergence is ever needed.
+ */
+
+/*
+ * Current version of the filter code architecture.
+ */
+#define SECCOMP_BPF_MAJOR_VERSION 1
+#define SECCOMP_BPF_MINOR_VERSION 1
+
+struct seccomp_filter_block { /* Filter block */
+ __u16 code; /* Actual filter code */
+ __u8 jt; /* Jump true */
+ __u8 jf; /* Jump false */
+ __u32 k; /* Generic multiuse field */
+};
+
+struct seccomp_fprog { /* Required for SO_ATTACH_FILTER. */
+ unsigned short len; /* Number of filter blocks */
+ struct seccomp_filter_block __user *filter;
+};
+
+/* Ensure the u32 ordering is consistent with platform byte order. */
+#if defined(__LITTLE_ENDIAN)
+#define SECCOMP_ENDIAN_SWAP(x, y) x, y
+#elif defined(__BIG_ENDIAN)
+#define SECCOMP_ENDIAN_SWAP(x, y) y, x
+#else
+#error edit for your odd arch byteorder.
+#endif
+
+/* System call argument layout for the filter data. */
+union seccomp_filter_arg {
+ struct {
+ __u32 SECCOMP_ENDIAN_SWAP(lo32, hi32);
+ };
+ __u64 u64;
+};
+
+/*
+ * Expected data the BPF program will execute over.
+ * Endianness will be arch specific, but the values will be
+ * swapped, as above, to allow for consistent BPF programs.
+ */
+struct seccomp_filter_data {
+ int syscall_nr;
+ __u32 __reserved;
+ union seccomp_filter_arg args[6];
+};
+
+#undef SECCOMP_ENDIAN_SWAP
+
+/*
+ * Defined valid return values for the BPF program.
+ */
+#define SECCOMP_BPF_ALLOW 0xFFFFFFFF
+#define SECCOMP_BPF_DENY 0
+
+#endif /* __LINUX_SECCOMP_FILTER_H__ */
diff --git a/kernel/Makefile b/kernel/Makefile
index 2d9de86..fd81bac 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -78,6 +78,7 @@ obj-$(CONFIG_DETECT_HUNG_TASK) += hung_task.o
obj-$(CONFIG_LOCKUP_DETECTOR) += watchdog.o
obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
obj-$(CONFIG_SECCOMP) += seccomp.o
+obj-$(CONFIG_SECCOMP_FILTER) += seccomp_filter.o
obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
obj-$(CONFIG_TREE_RCU) += rcutree.o
obj-$(CONFIG_TREE_PREEMPT_RCU) += rcutree.o
diff --git a/kernel/fork.c b/kernel/fork.c
index 051f090..0007933 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -34,6 +34,7 @@
#include <linux/cgroup.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
+#include <linux/seccomp.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/jiffies.h>
@@ -169,6 +170,7 @@ void free_task(struct task_struct *tsk)
free_thread_info(tsk->stack);
rt_mutex_debug_task_free(tsk);
ftrace_graph_exit_task(tsk);
+ seccomp_free_task(&tsk->seccomp);
free_task_struct(tsk);
}
EXPORT_SYMBOL(free_task);
@@ -1093,6 +1095,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
goto fork_out;

ftrace_graph_init_task(p);
+ seccomp_init_task(&p->seccomp);

rt_mutex_init_task(p);

@@ -1376,6 +1379,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
if (clone_flags & CLONE_THREAD)
threadgroup_change_end(current);
perf_event_fork(p);
+ seccomp_fork(&p->seccomp, &current->seccomp);

trace_task_newtask(p, clone_flags);

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index e8d76c5..a045dd4 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -37,7 +37,7 @@ void __secure_computing(int this_syscall)
int * syscall;

switch (mode) {
- case 1:
+ case SECCOMP_MODE_STRICT:
syscall = mode1_syscalls;
#ifdef CONFIG_COMPAT
if (is_compat_task())
@@ -48,6 +48,14 @@ void __secure_computing(int this_syscall)
return;
} while (*++syscall);
break;
+#ifdef CONFIG_SECCOMP_FILTER
+ case SECCOMP_MODE_FILTER:
+ if (seccomp_test_filters(this_syscall) == 0)
+ return;
+
+ seccomp_filter_log_failure(this_syscall);
+ break;
+#endif
default:
BUG();
}
diff --git a/kernel/seccomp_filter.c b/kernel/seccomp_filter.c
new file mode 100644
index 0000000..0e2e56c
--- /dev/null
+++ b/kernel/seccomp_filter.c
@@ -0,0 +1,627 @@
+/*
+ * linux/kernel/seccomp_filter.c
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ *
+ * Extends linux/kernel/seccomp.c to allow tasks to install system call
+ * filters using a Berkeley Packet Filter program which is executed over
+ * struct seccomp_filter_data.
+ */
+
+#include <asm/syscall.h>
+
+#include <linux/capability.h>
+#include <linux/compat.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/rculist.h>
+#include <linux/filter.h>
+#include <linux/kallsyms.h>
+#include <linux/kref.h>
+#include <linux/module.h>
+#include <linux/pid.h>
+#include <linux/prctl.h>
+#include <linux/ptrace.h>
+#include <linux/ratelimit.h>
+#include <linux/reciprocal_div.h>
+#include <linux/regset.h>
+#include <linux/seccomp.h>
+#include <linux/seccomp_filter.h>
+#include <linux/security.h>
+#include <linux/seccomp.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/user.h>
+
+
+/**
+ * struct seccomp_filter - container for seccomp BPF programs
+ *
+ * @usage: reference count to manage the object lifetime.
+ * get/put helpers should be used when accessing an instance
+ * outside of a lifetime-guarded section. In general, this
+ * is only needed for handling filters shared across tasks.
+ * @parent: pointer to the ancestor which this filter will be composed with.
+ * @insns: the BPF program instructions to evaluate
+ * @count: the number of instructions in the program.
+ *
+ * seccomp_filter objects should never be modified after being attached
+ * to a task_struct (other than @usage).
+ */
+struct seccomp_filter {
+ struct kref usage;
+ struct seccomp_filter *parent;
+ struct {
+ uint32_t compat:1;
+ } flags;
+ unsigned short count; /* Instruction count */
+ struct sock_filter insns[0];
+};
+
+/*
+ * struct seccomp_filter_metadata - BPF data wrapper
+ * @data: data accessible to the BPF program.
+ * @has_args: indicates that the args have been lazily populated.
+ *
+ * Used by seccomp_load_pointer.
+ */
+struct seccomp_filter_metadata {
+ struct seccomp_filter_data data;
+ bool has_args;
+};
+
+static unsigned int seccomp_run_filter(void *, uint32_t,
+ const struct sock_filter *);
+
+/**
+ * seccomp_filter_alloc - allocates a new filter object
+ * @padding: size of the insns[0] array in bytes
+ *
+ * The @padding should be a multiple of
+ * sizeof(struct sock_filter).
+ *
+ * Returns ERR_PTR on error or an allocated object.
+ */
+static struct seccomp_filter *seccomp_filter_alloc(unsigned long padding)
+{
+ struct seccomp_filter *f;
+ unsigned long bpf_blocks = padding / sizeof(struct sock_filter);
+
+ /* Drop oversized requests. */
+ if (bpf_blocks == 0 || bpf_blocks > BPF_MAXINSNS)
+ return ERR_PTR(-EINVAL);
+
+ /* Padding should always be in sock_filter increments. */
+ if (padding % sizeof(struct sock_filter))
+ return ERR_PTR(-EINVAL);
+
+ f = kzalloc(sizeof(struct seccomp_filter) + padding, GFP_KERNEL);
+ if (!f)
+ return ERR_PTR(-ENOMEM);
+ kref_init(&f->usage);
+ f->count = bpf_blocks;
+ return f;
+}
+
+/**
+ * seccomp_filter_free - frees the allocated filter.
+ * @filter: NULL or live object to be completely destructed.
+ */
+static void seccomp_filter_free(struct seccomp_filter *filter)
+{
+ if (!filter)
+ return;
+ put_seccomp_filter(filter->parent);
+ kfree(filter);
+}
+
+static void __put_seccomp_filter(struct kref *kref)
+{
+ struct seccomp_filter *orig =
+ container_of(kref, struct seccomp_filter, usage);
+ seccomp_filter_free(orig);
+}
+
+void seccomp_filter_log_failure(int syscall)
+{
+ int compat = 0;
+#ifdef CONFIG_COMPAT
+ compat = is_compat_task();
+#endif
+ pr_info("%s[%d]: %ssystem call %d blocked at 0x%lx\n",
+ current->comm, task_pid_nr(current),
+ (compat ? "compat " : ""),
+ syscall, KSTK_EIP(current));
+}
+
+/* put_seccomp_filter - decrements the ref count of @orig and may free. */
+void put_seccomp_filter(struct seccomp_filter *orig)
+{
+ if (!orig)
+ return;
+ kref_put(&orig->usage, __put_seccomp_filter);
+}
+
+/* get_seccomp_filter - increments the reference count of @orig. */
+struct seccomp_filter *get_seccomp_filter(struct seccomp_filter *orig)
+{
+ if (!orig)
+ return NULL;
+ kref_get(&orig->usage);
+ return orig;
+}
+
+#if BITS_PER_LONG == 32
+static inline unsigned long *seccomp_filter_data_arg(
+ struct seccomp_filter_data *data, int index)
+{
+ /* Avoid inconsistent hi contents. */
+ data->args[index].hi32 = 0;
+ return (unsigned long *) &(data->args[index].lo32);
+}
+#elif BITS_PER_LONG == 64
+static inline unsigned long *seccomp_filter_data_arg(
+ struct seccomp_filter_data *data, int index)
+{
+ return (unsigned long *) &(data->args[index].u64);
+}
+#else
+#error Unknown BITS_PER_LONG.
+#endif
+
+/**
+ * seccomp_load_pointer: checks and returns a pointer to the requested offset
+ * @buf: u8 array to index into
+ * @buflen: length of the @buf array
+ * @offset: offset to return data from
+ * @size: size of the data to retrieve at offset
+ * @unused: placeholder which net/core/filter.c uses for for temporary
+ * storage. Ideally, the two code paths can be merged.
+ *
+ * Returns a pointer to the BPF evaluator after checking the offset and size
+ * boundaries.
+ */
+static inline void *seccomp_load_pointer(void *data, int offset, size_t size,
+ void *buffer)
+{
+ struct seccomp_filter_metadata *metadata = data;
+ int arg;
+ if (offset >= sizeof(metadata->data))
+ goto fail;
+ if (offset < 0)
+ goto fail;
+ if (size > sizeof(metadata->data) - offset)
+ goto fail;
+ if (metadata->has_args)
+ goto pass;
+ /* No argument data touched. */
+ if (offset + size - 1 < offsetof(struct seccomp_filter_data, args))
+ goto pass;
+ for (arg = 0; arg < ARRAY_SIZE(metadata->data.args); ++arg)
+ syscall_get_arguments(current, task_pt_regs(current), arg, 1,
+ seccomp_filter_data_arg(&metadata->data, arg));
+ metadata->has_args = true;
+pass:
+ return ((__u8 *)(&metadata->data)) + offset;
+fail:
+ return NULL;
+}
+
+/**
+ * seccomp_test_filters - tests 'current' against the given syscall
+ * @syscall: number of the system call to test
+ *
+ * Returns 0 on ok and non-zero on error/failure.
+ */
+int seccomp_test_filters(int syscall)
+{
+ int ret = -EACCES;
+ struct seccomp_filter *filter;
+ struct seccomp_filter_metadata metadata;
+
+ filter = current->seccomp.filter; /* uses task ref */
+ if (!filter)
+ goto out;
+
+ metadata.data.syscall_nr = syscall;
+ metadata.has_args = false;
+
+#ifdef CONFIG_COMPAT
+ if (filter->flags.compat != !!(is_compat_task()))
+ goto out;
+#endif
+
+ /* Only allow a system call if it is allowed in all ancestors. */
+ ret = 0;
+ for ( ; filter != NULL; filter = filter->parent) {
+ /* Allowed if return value is SECCOMP_BPF_ALLOW */
+ if (seccomp_run_filter(&metadata, sizeof(metadata.data),
+ filter->insns) != SECCOMP_BPF_ALLOW)
+ ret = -EACCES;
+ }
+out:
+ return ret;
+}
+
+/**
+ * seccomp_attach_filter: Attaches a seccomp filter to current.
+ * @fprog: BPF program to install
+ *
+ * Context: User context only. This function may sleep on allocation and
+ * operates on current. current must be attempting a system call
+ * when this is called (usually prctl).
+ *
+ * This function may be called repeatedly to install additional filters.
+ * Every filter successfully installed will be evaluated (in reverse order)
+ * for each system call the thread makes.
+ *
+ * Returns 0 on success or an errno on failure.
+ */
+long seccomp_attach_filter(struct sock_fprog *fprog)
+{
+ struct seccomp_filter *filter = NULL;
+ /* Note, len is a short so overflow should be impossible. */
+ unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
+ long ret = -EPERM;
+
+ /* Allocate a new seccomp_filter */
+ filter = seccomp_filter_alloc(fp_size);
+ if (IS_ERR(filter)) {
+ ret = PTR_ERR(filter);
+ goto out;
+ }
+
+ /* Copy the instructions from fprog. */
+ ret = -EFAULT;
+ if (copy_from_user(filter->insns, fprog->filter, fp_size))
+ goto out;
+
+ /* Check the fprog */
+ ret = sk_chk_filter(filter->insns, filter->count);
+ if (ret)
+ goto out;
+
+ /*
+ * Installing a seccomp filter requires that the task
+ * have CAP_SYS_ADMIN in its namespace or be running with
+ * no_new_privs. This avoids scenarios where unprivileged
+ * tasks can affect the behavior of privileged children.
+ */
+ ret = -EACCES;
+ if (!current->no_new_privs &&
+ security_capable_noaudit(current_cred(), current_user_ns(),
+ CAP_SYS_ADMIN) != 0)
+ goto out;
+
+ /*
+ * If there is an existing filter, make it the parent
+ * and reuse the existing task-based ref.
+ */
+ filter->parent = current->seccomp.filter;
+
+#ifdef CONFIG_COMPAT
+ /* Disallow changing system calling conventions after the fact. */
+ filter->flags.compat = !!(is_compat_task());
+
+ if (filter->parent &&
+ filter->parent->flags.compat != filter->flags.compat)
+ goto out;
+#endif
+
+ /*
+ * Double claim the new filter so we can release it below simplifying
+ * the error paths earlier.
+ */
+ ret = 0;
+ get_seccomp_filter(filter);
+ current->seccomp.filter = filter;
+ /* Engage seccomp if it wasn't. This doesn't use PR_SET_SECCOMP. */
+ if (current->seccomp.mode == SECCOMP_MODE_DISABLED) {
+ current->seccomp.mode = SECCOMP_MODE_FILTER;
+ set_thread_flag(TIF_SECCOMP);
+ }
+
+out:
+ put_seccomp_filter(filter); /* for get or task, on err */
+ return ret;
+}
+
+#ifdef CONFIG_COMPAT
+/* This should be kept in sync with net/compat.c which changes infrequently. */
+struct compat_sock_fprog {
+ u16 len;
+ compat_uptr_t filter; /* struct sock_filter */
+};
+
+static long compat_attach_seccomp_filter(char __user *optval)
+{
+ struct compat_sock_fprog __user *fprog32 =
+ (struct compat_sock_fprog __user *)optval;
+ struct sock_fprog __user *kfprog =
+ compat_alloc_user_space(sizeof(struct sock_fprog));
+ compat_uptr_t ptr;
+ u16 len;
+
+ if (!access_ok(VERIFY_READ, fprog32, sizeof(*fprog32)) ||
+ !access_ok(VERIFY_WRITE, kfprog, sizeof(struct sock_fprog)) ||
+ __get_user(len, &fprog32->len) ||
+ __get_user(ptr, &fprog32->filter) ||
+ __put_user(len, &kfprog->len) ||
+ __put_user(compat_ptr(ptr), &kfprog->filter))
+ return -EFAULT;
+
+ return seccomp_attach_filter(kfprog);
+}
+#endif
+
+long prctl_attach_seccomp_filter(char __user *user_filter)
+{
+ struct sock_fprog fprog;
+ long ret = -EINVAL;
+ ret = -EFAULT;
+ if (!user_filter)
+ goto out;
+
+#ifdef CONFIG_COMPAT
+ if (is_compat_task())
+ return compat_attach_seccomp_filter(user_filter);
+#endif
+
+ if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
+ goto out;
+
+ ret = seccomp_attach_filter(&fprog);
+out:
+ return ret;
+}
+
+/**
+ * seccomp_fork: manages inheritance on fork
+ * @child: forkee's seccomp_struct
+ * @parent: forker's seccomp_struct
+ *
+ * Ensures that @child inherits seccomp mode and state iff
+ * seccomp filtering is in use.
+ */
+void seccomp_fork(struct seccomp_struct *child,
+ const struct seccomp_struct *parent)
+{
+ child->mode = parent->mode;
+ if (parent->mode != SECCOMP_MODE_FILTER)
+ return;
+ child->filter = get_seccomp_filter(parent->filter);
+}
+
+/**
+ * seccomp_run_filter - evaluate BPF
+ * @buf: opaque buffer to execute the filter over
+ * @buflen: length of the buffer
+ * @fentry: filter to apply
+ *
+ * Decode and apply filter instructions to the buffer. Return length to
+ * keep, 0 for none. @buf is a seccomp_filter_metadata we are filtering,
+ * @filter is the array of filter instructions. Because all jumps are
+ * guaranteed to be before last instruction, and last instruction
+ * guaranteed to be a RET, we dont need to check flen.
+ *
+ * See core/net/filter.c as this is nearly an exact copy.
+ * At some point, it would be nice to merge them to take advantage of
+ * optimizations (like JIT).
+ */
+static unsigned int seccomp_run_filter(void *data, uint32_t datalen,
+ const struct sock_filter *fentry)
+{
+ const void *ptr;
+ u32 A = 0; /* Accumulator */
+ u32 X = 0; /* Index Register */
+ u32 mem[BPF_MEMWORDS]; /* Scratch Memory Store */
+ u32 tmp;
+ int k;
+
+ /*
+ * Process array of filter instructions.
+ */
+ for (;; fentry++) {
+#if defined(CONFIG_X86_32)
+#define K (fentry->k)
+#else
+ const u32 K = fentry->k;
+#endif
+
+ switch (fentry->code) {
+ case BPF_S_ALU_ADD_X:
+ A += X;
+ continue;
+ case BPF_S_ALU_ADD_K:
+ A += K;
+ continue;
+ case BPF_S_ALU_SUB_X:
+ A -= X;
+ continue;
+ case BPF_S_ALU_SUB_K:
+ A -= K;
+ continue;
+ case BPF_S_ALU_MUL_X:
+ A *= X;
+ continue;
+ case BPF_S_ALU_MUL_K:
+ A *= K;
+ continue;
+ case BPF_S_ALU_DIV_X:
+ if (X == 0)
+ return 0;
+ A /= X;
+ continue;
+ case BPF_S_ALU_DIV_K:
+ A = reciprocal_divide(A, K);
+ continue;
+ case BPF_S_ALU_AND_X:
+ A &= X;
+ continue;
+ case BPF_S_ALU_AND_K:
+ A &= K;
+ continue;
+ case BPF_S_ALU_OR_X:
+ A |= X;
+ continue;
+ case BPF_S_ALU_OR_K:
+ A |= K;
+ continue;
+ case BPF_S_ALU_LSH_X:
+ A <<= X;
+ continue;
+ case BPF_S_ALU_LSH_K:
+ A <<= K;
+ continue;
+ case BPF_S_ALU_RSH_X:
+ A >>= X;
+ continue;
+ case BPF_S_ALU_RSH_K:
+ A >>= K;
+ continue;
+ case BPF_S_ALU_NEG:
+ A = -A;
+ continue;
+ case BPF_S_JMP_JA:
+ fentry += K;
+ continue;
+ case BPF_S_JMP_JGT_K:
+ fentry += (A > K) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_JMP_JGE_K:
+ fentry += (A >= K) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_JMP_JEQ_K:
+ fentry += (A == K) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_JMP_JSET_K:
+ fentry += (A & K) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_JMP_JGT_X:
+ fentry += (A > X) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_JMP_JGE_X:
+ fentry += (A >= X) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_JMP_JEQ_X:
+ fentry += (A == X) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_JMP_JSET_X:
+ fentry += (A & X) ? fentry->jt : fentry->jf;
+ continue;
+ case BPF_S_LD_W_ABS:
+ k = K;
+load_w:
+ ptr = seccomp_load_pointer(data, k, 4, &tmp);
+ if (ptr != NULL) {
+ /*
+ * Assume load_pointer did any byte swapping.
+ */
+ A = *(const u32 *)ptr;
+ continue;
+ }
+ return 0;
+ case BPF_S_LD_H_ABS:
+ k = K;
+load_h:
+ ptr = seccomp_load_pointer(data, k, 2, &tmp);
+ if (ptr != NULL) {
+ A = *(const u16 *)ptr;
+ continue;
+ }
+ return 0;
+ case BPF_S_LD_B_ABS:
+ k = K;
+load_b:
+ ptr = seccomp_load_pointer(data, k, 1, &tmp);
+ if (ptr != NULL) {
+ A = *(const u8 *)ptr;
+ continue;
+ }
+ return 0;
+ case BPF_S_LD_W_LEN:
+ A = datalen;
+ continue;
+ case BPF_S_LDX_W_LEN:
+ X = datalen;
+ continue;
+ case BPF_S_LD_W_IND:
+ k = X + K;
+ goto load_w;
+ case BPF_S_LD_H_IND:
+ k = X + K;
+ goto load_h;
+ case BPF_S_LD_B_IND:
+ k = X + K;
+ goto load_b;
+ case BPF_S_LDX_B_MSH:
+ ptr = seccomp_load_pointer(data, K, 1, &tmp);
+ if (ptr != NULL) {
+ X = (*(u8 *)ptr & 0xf) << 2;
+ continue;
+ }
+ return 0;
+ case BPF_S_LD_IMM:
+ A = K;
+ continue;
+ case BPF_S_LDX_IMM:
+ X = K;
+ continue;
+ case BPF_S_LD_MEM:
+ A = mem[K];
+ continue;
+ case BPF_S_LDX_MEM:
+ X = mem[K];
+ continue;
+ case BPF_S_MISC_TAX:
+ X = A;
+ continue;
+ case BPF_S_MISC_TXA:
+ A = X;
+ continue;
+ case BPF_S_RET_K:
+ return K;
+ case BPF_S_RET_A:
+ return A;
+ case BPF_S_ST:
+ mem[K] = A;
+ continue;
+ case BPF_S_STX:
+ mem[K] = X;
+ continue;
+ case BPF_S_ANC_PROTOCOL:
+ case BPF_S_ANC_PKTTYPE:
+ case BPF_S_ANC_IFINDEX:
+ case BPF_S_ANC_MARK:
+ case BPF_S_ANC_QUEUE:
+ case BPF_S_ANC_HATYPE:
+ case BPF_S_ANC_RXHASH:
+ case BPF_S_ANC_CPU:
+ case BPF_S_ANC_NLATTR:
+ case BPF_S_ANC_NLATTR_NEST:
+ continue;
+ default:
+ WARN_RATELIMIT(1, "Unknown code:%u jt:%u tf:%u k:%u\n",
+ fentry->code, fentry->jt,
+ fentry->jf, fentry->k);
+ return 0;
+ }
+ }
+
+ return 0;
+}
diff --git a/kernel/sys.c b/kernel/sys.c
index 4070153..8e43f70 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1901,6 +1901,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
case PR_SET_SECCOMP:
error = prctl_set_seccomp(arg2);
break;
+ case PR_ATTACH_SECCOMP_FILTER:
+ error = prctl_attach_seccomp_filter((char __user *)
+ arg2);
+ break;
case PR_GET_TSC:
error = GET_TSC_CTL(arg2);
break;
diff --git a/security/Kconfig b/security/Kconfig
index 51bd5a0..3c55d36 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -84,6 +84,26 @@ config SECURITY_DMESG_RESTRICT

If you are unsure how to answer this question, answer N.

+config SECCOMP_FILTER
+ bool "Enable seccomp-based system call filtering"
+ select SECCOMP
+ help
+ This option provides support for limiting the accessibility of
+ system calls at a task-level using a dynamically defined policy.
+
+ System call filtering policy is expressed as a Berkeley Packet
+ Filter program. The program is attached using prctl(2) and
+ cannot be detached. Once attached, the filter program will
+ evaluate each system call, and its arguments, the task
+ makes. Its output determines if the system call may proceed.
+ If the system call is disallowed, the task will be terminated
+ immediately.
+
+ Dynamically limiting system call access aids software in the
+ creation of secure computation environments.
+
+ See Documentation/prctl/seccomp_filter.txt for more detail.
+
config SECURITY
bool "Enable different security models"
depends on SYSFS
--
1.7.5.4


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