mirror of
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.
113 lines
4.8 KiB
C
113 lines
4.8 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/calls/calls.h"
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#include "libc/dns/consts.h"
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#include "libc/dns/dns.h"
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#include "libc/dns/dnsheader.h"
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#include "libc/dns/dnsquestion.h"
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#include "libc/dns/resolvconf.h"
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#include "libc/intrin/bits.h"
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#include "libc/mem/mem.h"
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#include "libc/runtime/runtime.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/stdio/rand.h"
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#include "libc/stdio/stdio.h"
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#include "libc/str/str.h"
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#include "libc/sysv/consts/af.h"
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#include "libc/sysv/consts/ipproto.h"
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#include "libc/sysv/consts/sock.h"
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#include "libc/sysv/errfuns.h"
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#define kMsgMax 512
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/**
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* Queries Domain Name System for address associated with name.
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*
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* @param resolvconf can be GetResolvConf()
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* @param af can be AF_INET, AF_UNSPEC
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* @param name can be a local or fully-qualified hostname
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* @param addr should point to a struct sockaddr_in; if this function
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* succeeds, its sin_family and sin_addr fields will be modified
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* @param addrsize is the byte size of addr
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* @return number of matches found, or -1 w/ errno
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* @error EAFNOSUPPORT. ENETDOWN, ENAMETOOLONG, EBADMSG
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*/
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int ResolveDns(const struct ResolvConf *resolvconf, int af, const char *name,
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struct sockaddr *addr, uint32_t addrsize) {
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int32_t ttl;
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int rc, fd, n;
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struct DnsQuestion q;
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struct DnsHeader h, h2;
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struct sockaddr_in *a4;
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uint8_t *p, *pe, msg[512];
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uint16_t rtype, rclass, rdlength;
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if (addrsize < kMinSockaddr4Size) return einval();
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if (af != AF_INET && af != AF_UNSPEC) return eafnosupport();
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if (!resolvconf->nameservers.i) return 0;
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bzero(&h, sizeof(h));
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rc = ebadmsg();
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h.id = rand64();
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h.bf1 = 1; /* recursion desired */
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h.qdcount = 1;
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q.qname = name;
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q.qtype = DNS_TYPE_A;
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q.qclass = DNS_CLASS_IN;
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bzero(msg, sizeof(msg));
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SerializeDnsHeader(msg, &h);
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if ((n = SerializeDnsQuestion(msg + 12, 500, &q)) == -1) return -1;
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if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) return -1;
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if (sendto(fd, msg, 12 + n, 0, resolvconf->nameservers.p,
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sizeof(*resolvconf->nameservers.p)) == 12 + n &&
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(n = read(fd, msg, 512)) >= 12) {
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DeserializeDnsHeader(&h2, msg);
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if (h2.id == h.id) {
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rc = 0;
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p = msg + 12;
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pe = msg + n;
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while (p < pe && h2.qdcount--) {
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p += strnlen((char *)p, pe - p) + 1 + 4;
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}
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while (p < pe && h2.ancount--) {
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if ((p[0] & 0xc0) == 0xc0) { /* name pointer */
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p += 2;
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} else {
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p += strnlen((char *)p, pe - p) + 1;
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}
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if (p + 10 <= pe) {
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rtype = READ16BE(p);
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rclass = READ16BE(p + 2);
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ttl = READ32BE(p + 4);
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rdlength = READ16BE(p + 8);
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if (p + 10 + rdlength <= pe && rdlength == 4 &&
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rclass == DNS_CLASS_IN && rtype == DNS_TYPE_A) {
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rc = 1;
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a4 = (struct sockaddr_in *)addr;
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a4->sin_family = AF_INET;
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memcpy(&a4->sin_addr.s_addr, p + 10, 4);
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break;
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}
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p += 10 + rdlength;
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}
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}
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}
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}
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close(fd);
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return rc;
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}
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