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restrict_process_seccomp.c
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restrict_process_seccomp.c
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/* Copyright (c) 2019-2021, Michael Santos <michael.santos@gmail.com>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include "restrict_process.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 RESTRICT_PROCESS_SECCOMP_FILTER_DEBUG
#undef SECCOMP_FILTER_FAIL
#define SECCOMP_FILTER_FAIL SECCOMP_RET_TRAP
#endif /* RESTRICT_PROCESS_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 disable_setuid_subprocess(void) {
return prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
}
int restrict_process_signal_on_supervisor_exit(void) {
return prctl(PR_SET_PDEATHSIG, 9);
}
int restrict_process_init(void) { return 0; }
int restrict_process(void) {
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
/* /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_write
SC_ALLOW(write),
#endif
#ifdef __NR_writev
SC_ALLOW(writev),
#endif
#ifdef __NR_restart_syscall
SC_ALLOW(restart_syscall),
#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);
}
int restrict_process_wait(int fdp) {
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_exit_group
SC_ALLOW(exit_group),
#endif
/* stdio */
#ifdef __NR_write
SC_ALLOW(write),
#endif
#ifdef __NR_writev
SC_ALLOW(writev),
#endif
#ifdef __NR_restart_syscall
SC_ALLOW(restart_syscall),
#endif
#ifdef __NR_rt_sigaction
SC_ALLOW(rt_sigaction),
#endif
#ifdef __NR_rt_sigprocmask
SC_ALLOW(rt_sigprocmask),
#endif
#ifdef __NR_sigprocmask
SC_ALLOW(sigprocmask),
#endif
#ifdef __NR_rt_sigreturn
SC_ALLOW(rt_sigreturn),
#endif
#ifdef __NR_sigreturn
SC_ALLOW(sigreturn),
#endif
#ifdef __NR_wait4
SC_ALLOW(wait4),
#endif
#ifdef __NR_alarm
SC_ALLOW(alarm),
#endif
#ifdef __NR_setitimer
SC_ALLOW(setitimer),
#endif
#ifdef __NR_lseek
SC_ALLOW(lseek),
#endif
#ifdef __NR__llseek
SC_ALLOW(_llseek),
#endif
#ifdef __NR_kill
SC_ALLOW(kill),
#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,
};
(void)fdp;
return prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
}
#endif