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https://github.com/jart/cosmopolitan.git
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7cf66bc161
This change introduces the nointernet() function which may be called to prevent a process and its descendants from communicating with publicly routable Internet addresses. GNU Make has been modified to always call this function. In the future Landlock Make will have a way to whitelist subnets to override this behavior, or disable it entirely. Support is available for Linux only. Our firewall does not require root access. Calling nointernet() will return control to the caller inside a new process that has a SECCOMP BPF filter installed, which traps network related system calls. Your original process then becomes a permanent ptrace() supervisor that monitors all processes and threads descending from the returned child. Whenever a networking system call happens the kernel will stop the process and wakes up the monitor, which then peeks into the child memory to read the sockaddr_in to determine if it's ok. The downside to doing this is that there can be only one supervisor at a time using ptrace() on a process. So this firewall won't be enabled if you run make under strace or inside gdb. It also makes testing tricky.
90 lines
4.4 KiB
C
90 lines
4.4 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/assert.h"
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#include "libc/calls/internal.h"
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#include "libc/calls/strace.internal.h"
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#include "libc/calls/struct/iovec.h"
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#include "libc/dce.h"
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#include "libc/intrin/asan.internal.h"
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#include "libc/macros.internal.h"
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#include "libc/sock/internal.h"
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#include "libc/sock/sock.h"
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#include "libc/str/str.h"
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#include "libc/sysv/errfuns.h"
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/**
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* Sends data over network.
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*
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* This function blocks unless MSG_DONTWAIT is passed. In that case, the
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* non-error EWOULDBLOCK might be returned. It basically means we didn't
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* wait around to learn an amount of bytes were written that we know in
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* advance are guaranteed to be atomic.
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*
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* @param fd is the file descriptor returned by socket()
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* @param buf is the data to send, which we'll copy if necessary
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* @param size is the byte-length of buf
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* @param flags MSG_OOB, MSG_DONTROUTE, MSG_PARTIAL, MSG_NOSIGNAL, etc.
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* @param opt_addr is a binary ip:port destination override, which is
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* mandatory for UDP if connect() wasn't called
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* @param addrsize is the byte-length of addr's true polymorphic form
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* @return number of bytes transmitted, or -1 w/ errno
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* @error EINTR, EHOSTUNREACH, ECONNRESET (UDP ICMP Port Unreachable),
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* EPIPE (if MSG_NOSIGNAL), EMSGSIZE, ENOTSOCK, EFAULT, etc.
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* @asyncsignalsafe
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* @restartable (unless SO_RCVTIMEO)
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*/
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ssize_t sendto(int fd, const void *buf, size_t size, uint32_t flags,
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const void *opt_addr, uint32_t addrsize) {
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ssize_t rc;
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uint32_t bsdaddrsize;
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union sockaddr_storage_bsd bsd;
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if (IsAsan() && (!__asan_is_valid(buf, size) ||
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(opt_addr && !__asan_is_valid(opt_addr, addrsize)))) {
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rc = efault();
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} else {
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if (!IsWindows()) {
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if (!IsBsd() || !opt_addr) {
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rc = sys_sendto(fd, buf, size, flags, opt_addr, addrsize);
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} else if (!(rc = sockaddr2bsd(opt_addr, addrsize, &bsd, &bsdaddrsize))) {
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rc = sys_sendto(fd, buf, size, flags, &bsd, bsdaddrsize);
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}
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} else if (__isfdopen(fd)) {
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if (__isfdkind(fd, kFdSocket)) {
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rc = sys_sendto_nt(fd, (struct iovec[]){{buf, size}}, 1, flags,
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opt_addr, addrsize);
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} else if (__isfdkind(fd, kFdFile)) {
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if (flags) {
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rc = einval();
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} else if (opt_addr) {
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rc = eisconn();
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} else {
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rc = sys_write_nt(fd, (struct iovec[]){{buf, size}}, 1, -1);
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}
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} else {
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rc = enotsock();
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}
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} else {
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rc = ebadf();
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}
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}
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DATATRACE("sendto(%d, %#.*hhs%s, %'zu, %#x, %p, %u) → %'ld% lm", fd,
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MAX(0, MIN(40, rc)), buf, rc > 40 ? "..." : "", size, flags,
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opt_addr, addrsize, rc);
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return rc;
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}
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