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restrict_process_seccomp.c
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/* Copyright 2018-2022 Michael Santos <michael.santos@gmail.com>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "pseudocron.h"
#ifdef RESTRICT_PROCESS_seccomp
#include <errno.h>
#include <stddef.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <linux/audit.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
/* macros from openssh-7.2/sandbox-seccomp-filter.c */
/* Linux seccomp_filter sandbox */
#define SECCOMP_FILTER_FAIL SECCOMP_RET_KILL
/* Use a signal handler to emit violations when debugging */
#ifdef SANDBOX_SECCOMP_FILTER_DEBUG
#undef SECCOMP_FILTER_FAIL
#define SECCOMP_FILTER_FAIL SECCOMP_RET_TRAP
#endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
/* Simple helpers to avoid manual errors (but larger BPF programs). */
#define SC_DENY(_nr, _errno) \
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, __NR_##_nr, 0, 1), \
BPF_STMT(BPF_RET + BPF_K, SECCOMP_RET_ERRNO | (_errno))
#define SC_ALLOW(_nr) \
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, __NR_##_nr, 0, 1), \
BPF_STMT(BPF_RET + BPF_K, SECCOMP_RET_ALLOW)
#define SC_ALLOW_ARG(_nr, _arg_nr, _arg_val) \
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, __NR_##_nr, 0, \
4), /* load first syscall argument */ \
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, \
offsetof(struct seccomp_data, args[(_arg_nr)])), \
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (_arg_val), 0, 1), \
BPF_STMT(BPF_RET + BPF_K, \
SECCOMP_RET_ALLOW), /* reload syscall number; all rules expect \
it in accumulator */ \
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct seccomp_data, nr))
/*
* http://outflux.net/teach-seccomp/
* https://github.com/gebi/teach-seccomp
*
*/
#define syscall_nr (offsetof(struct seccomp_data, nr))
#define arch_nr (offsetof(struct seccomp_data, arch))
#if defined(__i386__)
#define SECCOMP_AUDIT_ARCH AUDIT_ARCH_I386
#elif defined(__x86_64__)
#define SECCOMP_AUDIT_ARCH AUDIT_ARCH_X86_64
#elif defined(__arm__)
#define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ARM
#elif defined(__aarch64__)
#define SECCOMP_AUDIT_ARCH AUDIT_ARCH_AARCH64
#else
#warning "seccomp: unsupported platform"
#define SECCOMP_AUDIT_ARCH 0
#endif
int restrict_process_init() {
struct sock_filter filter[] = {
/* Ensure the syscall arch convention is as expected. */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct seccomp_data, arch)),
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SECCOMP_AUDIT_ARCH, 1, 0),
BPF_STMT(BPF_RET + BPF_K, SECCOMP_FILTER_FAIL),
/* Load the syscall number for checking. */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct seccomp_data, nr)),
/* Syscalls to non-fatally deny */
/* Syscalls to allow */
#ifdef __NR_brk
SC_ALLOW(brk),
#endif
#ifdef __NR_exit_group
SC_ALLOW(exit_group),
#endif
#ifdef __NR_nanosleep
SC_ALLOW(nanosleep),
#endif
#ifdef __NR_clock_getres
SC_ALLOW(clock_getres),
#endif
#ifdef __NR_clock_gettime
SC_ALLOW(clock_gettime),
#endif
#ifdef __NR_clock_gettime64
SC_ALLOW(clock_gettime64),
#endif
#ifdef __NR_gettimeofday
SC_ALLOW(gettimeofday),
#endif
/* /etc/localtime */
#ifdef __NR_fstat
SC_ALLOW(fstat),
#endif
#ifdef __NR_fstat64
SC_ALLOW(fstat64),
#endif
#ifdef __NR_stat
SC_ALLOW(stat),
#endif
#ifdef __NR_stat64
SC_ALLOW(stat64),
#endif
#ifdef __NR_newfstatat
SC_ALLOW(newfstatat),
#endif
/* stdio */
#ifdef __NR_read
SC_ALLOW(read),
#endif
#ifdef __NR_readv
SC_ALLOW(readv),
#endif
#ifdef __NR_write
SC_ALLOW(write),
#endif
#ifdef __NR_writev
SC_ALLOW(writev),
#endif
/* sigwinch */
#ifdef __NR_ioctl
SC_ALLOW(ioctl),
#endif
#ifdef __NR_restart_syscall
SC_ALLOW(restart_syscall),
#endif
#ifdef __NR_mmap
SC_ALLOW(mmap),
#endif
#ifdef __NR_mprotect
SC_ALLOW(mprotect),
#endif
#ifdef __NR_munmap
SC_ALLOW(munmap),
#endif
/* Default deny */
BPF_STMT(BPF_RET + BPF_K, SECCOMP_FILTER_FAIL)};
struct sock_fprog prog = {
.len = (unsigned short)(sizeof(filter) / sizeof(filter[0])),
.filter = filter,
};
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0)
return -1;
return prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
}
#endif