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/*
* Copyright (c) 2021 Omar Polo <op@omarpolo.com>
*
* Permission to use, copy, modify, and 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 "gmid.h"
#if defined(__FreeBSD__)
#include <sys/capsicum.h>
#include <err.h>
void
sandbox()
{
if (cap_enter() == -1)
err(1, "cap_enter");
}
#elif defined(__linux__)
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <linux/audit.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
/* thanks chromium' src/seccomp.c */
#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
#elif defined(__mips__)
# if defined(__mips64)
# if defined(__MIPSEB__)
# define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPS64
# else
# define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPSEL64
# endif
# else
# if defined(__MIPSEB__)
# define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPS
# else
# define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPSEL
# endif
# endif
#else
# error "Platform does not support seccomp filter yet"
#endif
/* uncomment to enable debugging. ONLY FOR DEVELOPMENT */
/* #define SC_DEBUG */
#ifdef SC_DEBUG
# define SC_FAIL SECCOMP_RET_TRAP
#else
# define SC_FAIL SECCOMP_RET_KILL
#endif
/* make the filter more readable */
#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)
#ifdef SC_DEBUG
#include <signal.h>
#include <unistd.h>
static void
sandbox_seccomp_violation(int signum, siginfo_t *info, void *ctx)
{
(void)signum;
(void)ctx;
fprintf(stderr, "%s: unexpected system call (arch:0x%x,syscall:%d @ %p)\n",
__func__, info->si_arch, info->si_syscall, info->si_call_addr);
_exit(1);
}
static void
sandbox_seccomp_catch_sigsys(void)
{
struct sigaction act;
sigset_t mask;
memset(&act, 0, sizeof(act));
sigemptyset(&mask);
sigaddset(&mask, SIGSYS);
act.sa_sigaction = &sandbox_seccomp_violation;
act.sa_flags = SA_SIGINFO;
if (sigaction(SIGSYS, &act, NULL) == -1) {
fprintf(stderr, "%s: sigaction(SIGSYS): %s\n",
__func__, strerror(errno));
exit(1);
}
if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1) {
fprintf(stderr, "%s: sigprocmask(SIGSYS): %s\n",
__func__, strerror(errno));
exit(1);
}
}
#endif /* SC_DEBUG */
void
sandbox()
{
struct sock_filter filter[] = {
/* load the *current* architecture */
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, arch))),
/* ensure it's the same that we've been compiled on */
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,
SECCOMP_AUDIT_ARCH, 1, 0),
/* if not, kill the program */
BPF_STMT(BPF_RET | BPF_K, SC_FAIL),
/* load the syscall number */
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, nr))),
/* allow logging on stdout */
SC_ALLOW(write),
SC_ALLOW(writev),
SC_ALLOW(readv),
/* these are used to serve the files. note how we
* allow openat but not open. */
#ifdef __aarch64__
/* it seems that on aarch64 there isn't a poll(2)
* syscall, but instead it's implemented on top of
* ppoll(2). */
SC_ALLOW(ppoll),
#else
SC_ALLOW(poll),
#endif
SC_ALLOW(accept),
SC_ALLOW(read),
SC_ALLOW(openat),
SC_ALLOW(fstat),
SC_ALLOW(close),
SC_ALLOW(lseek),
SC_ALLOW(brk),
SC_ALLOW(mmap),
SC_ALLOW(munmap),
/* we need recvmsg to receive fd */
SC_ALLOW(recvmsg),
/* XXX: ??? */
SC_ALLOW(getpid),
/* alpine on amd64 does a clock_gettime(2) */
SC_ALLOW(clock_gettime),
/* for directory listing */
SC_ALLOW(getdents64),
SC_ALLOW(exit),
SC_ALLOW(exit_group),
/* allow only F_GETFL and F_SETFL fcntl */
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_fcntl, 0, 8),
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, args[1]))),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, F_GETFL, 0, 1),
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, F_SETFL, 0, 1),
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, F_SETFD, 0, 1),
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
BPF_STMT(BPF_RET | BPF_K, SC_FAIL),
/* re-load the syscall number */
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, nr))),
/* allow ioctl but only on fd 1, glibc doing stuff? */
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_ioctl, 0, 3),
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, args[0]))),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1, 0, 1),
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
/* disallow enything else */
BPF_STMT(BPF_RET | BPF_K, SC_FAIL),
};
struct sock_fprog prog = {
.len = (unsigned short) (sizeof(filter) / sizeof(filter[0])),
.filter = filter,
};
#ifdef SC_DEBUG
sandbox_seccomp_catch_sigsys();
#endif
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) {
fprintf(stderr, "%s: prctl(PR_SET_NO_NEW_PRIVS): %s\n",
__func__, strerror(errno));
exit(1);
}
if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) == -1) {
fprintf(stderr, "%s: prctl(PR_SET_SECCOMP): %s\n",
__func__, strerror(errno));
exit(1);
}
}
#elif defined(__OpenBSD__)
#include <err.h>
#include <unistd.h>
void
sandbox()
{
struct vhost *h;
for (h = hosts; h->domain != NULL; ++h) {
if (unveil(h->dir, "r") == -1)
err(1, "unveil %s for domain %s", h->dir, h->domain);
}
if (pledge("stdio recvfd rpath inet", NULL) == -1)
err(1, "pledge");
}
#else
void
sandbox()
{
LOGN(NULL, "%s", "no sandbox method known for this OS");
}
#endif
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