/* * Copyright 2018 The Android Open Source Project * * 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. * * main.c - main function */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "clatd.h" #include "common.h" #include "config.h" #include "logging.h" #define DEVICEPREFIX "v4-" /* function: handle_sigterm * signal handler: stop the event loop */ static void handle_sigterm(__attribute__((unused)) int unused) { sigterm = 1; }; /* function: print_help * in case the user is running this on the command line */ void print_help() { printf("android-clat arguments:\n"); printf("-i [uplink interface]\n"); printf("-p [plat prefix]\n"); printf("-4 [IPv4 address]\n"); printf("-6 [IPv6 address]\n"); printf("-t [tun file descriptor number]\n"); printf("-r [read socket descriptor number]\n"); printf("-w [write socket descriptor number]\n"); } // Load the architecture identifier (AUDIT_ARCH_* constant) #define BPF_SECCOMP_LOAD_AUDIT_ARCH \ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct seccomp_data, arch)) // Load the system call number #define BPF_SECCOMP_LOAD_SYSCALL_NR \ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct seccomp_data, nr)) #if __BYTE_ORDER == __LITTLE_ENDIAN // Load the system call argument n, where n is [0..5] #define BPF_SECCOMP_LOAD_SYSCALL_ARG_LO32(n) \ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct seccomp_data, args[n])) #define BPF_SECCOMP_LOAD_SYSCALL_ARG_HI32(n) \ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct seccomp_data, args[n]) + 4) #else #error "Not a little endian architecture?" #endif // Allow the system call #define BPF_SECCOMP_ALLOW BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW) // Allow (but 'audit' log) the system call #define BPF_SECCOMP_LOG BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_LOG) // Reject the system call (kill thread) #define BPF_SECCOMP_KILL BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL) // Note arguments to BPF_JUMP(opcode, operand, true_offset, false_offset) // If not equal, jump over count instructions #define BPF_JUMP_IF_NOT_EQUAL(v, count) \ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (v), 0, (count)) // If equal, jump over count instructions #define BPF_JUMP_IF_EQUAL(v, count) \ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (v), (count), 0) // *TWO* instructions: compare and if not equal jump over the allow statement #define BPF2_SECCOMP_ALLOW_IF_EQUAL(v) \ BPF_JUMP_IF_NOT_EQUAL((v), 1), \ BPF_SECCOMP_ALLOW // *TWO* instructions: compare and if not equal jump over the log statement #define BPF2_SECCOMP_LOG_IF_EQUAL(v) \ BPF_JUMP_IF_NOT_EQUAL((v), 1), \ BPF_SECCOMP_LOG // *TWO* instructions: compare and if equal jump over the kill statement #define BPF2_SECCOMP_KILL_IF_NOT_EQUAL(v) \ BPF_JUMP_IF_EQUAL((v), 1), \ BPF_SECCOMP_KILL // Android only supports the following 5 little endian architectures #if defined(__aarch64__) && defined(__LP64__) #define MY_AUDIT_ARCH AUDIT_ARCH_AARCH64 #elif defined(__arm__) && defined(__ILP32__) #define MY_AUDIT_ARCH AUDIT_ARCH_ARM #elif defined(__i386__) && defined(__ILP32__) #define MY_AUDIT_ARCH AUDIT_ARCH_I386 #elif defined(__x86_64__) && defined(__LP64__) #define MY_AUDIT_ARCH AUDIT_ARCH_X86_64 #elif defined(__riscv) && defined(__LP64__) #define MY_AUDIT_ARCH AUDIT_ARCH_RISCV64 #else #error "Unknown AUDIT_ARCH_* architecture." #endif void enable_seccomp(void) { static const struct sock_filter filter[] = { BPF_SECCOMP_LOAD_AUDIT_ARCH, BPF2_SECCOMP_KILL_IF_NOT_EQUAL(MY_AUDIT_ARCH), BPF_SECCOMP_LOAD_SYSCALL_NR, // aarch64 // main event loop: // ppoll ( read sendmsg | recvmsg writev ) BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_ppoll), // 73 BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_read), // 63 BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_sendmsg), // 211 BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_recvmsg), // 212 BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_writev), // 66 // logging: getuid writev BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_getuid), // 174 // inbound signal (SIGTERM) processing BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_rt_sigreturn), // 139 // sleep(n) BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_nanosleep), // 101 // _exit(0) BPF2_SECCOMP_ALLOW_IF_EQUAL(__NR_exit_group), // 94 #if defined(__aarch64__) // Pixels are aarch64 - if we break clatd functionality on them, // we *will* notice on GoogleGuest WiFi network (which is ipv6 only) BPF_SECCOMP_KILL, #else // All other architectures: generate audit lines visible in dmesg and logcat BPF_SECCOMP_LOG, #endif }; static const struct sock_fprog prog = { .len = (unsigned short)ARRAY_SIZE(filter), .filter = (struct sock_filter *)filter, }; // https://man7.org/linux/man-pages/man2/PR_SET_NO_NEW_PRIVS.2const.html // required to allow non-privileged seccomp filter installation int rv = prctl(PR_SET_NO_NEW_PRIVS, 1L, 0L, 0L, 0L); if (rv) { logmsg(ANDROID_LOG_FATAL, "prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) = %d [%d]", rv, errno); exit(1); } // https://man7.org/linux/man-pages/man2/PR_SET_SECCOMP.2const.html // but see also https://man7.org/linux/man-pages/man2/seccomp.2.html rv = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog, 0L, 0L); if (rv) { logmsg(ANDROID_LOG_FATAL, "prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog, 0, 0) = %d [%d]", rv, errno); exit(1); } } /* function: main * allocate and setup the tun device, then run the event loop */ int main(int argc, char **argv) { struct tun_data tunnel; int opt; char *uplink_interface = NULL, *plat_prefix = NULL; char *v4_addr = NULL, *v6_addr = NULL, *tunfd_str = NULL, *read_sock_str = NULL, *write_sock_str = NULL; unsigned len; // Clatd binary is setuid/gid CLAT, thus when we reach here we have: // $ adb shell ps | grep clat // [pid] [ppid] // clat 7650 1393 10785364 2612 do_sys_poll 0 S clatd-wlan0 // $ adb shell cat /proc/7650/status | egrep -i '^(Uid:|Gid:|Groups:)' // [real][effective][saved][filesystem] // [uid] [euid] [suid] [fsuid] // Uid: 1000 1029 1029 1029 // [gid] [egid] [sgid] [fsgid] // Gid: 1000 1029 1029 1029 // Groups: 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1018 1021 1023 1024 1032 1065 3001 3002 3003 3005 3006 3007 3009 3010 3011 3012 // This mismatch between uid & euid appears to cause periodic (every 5 minutes): // objhash pid ppid uid // W ActivityManager: Stale PhantomProcessRecord {xxxxxxx 7650:1393:clatd-wlan0/1000}, removing // This is due to: // $ adbz shell ls -ld /proc/7650 // dr-xr-xr-x 9 clat clat 0 2025-03-14 11:37 /proc/7650 // which is used by // //frameworks/base/core/java/com/android/internal/os/ProcessCpuTracker.java // which thus returns the uid 'clat' vs // //frameworks/base/core/java/android/os/Process.java // getUidForPid() which grabs *real* 'uid' from /proc//status and is used in: // //frameworks/base/services/core/java/com/android/server/am/PhantomProcessList.java // (perhaps this should grab euid instead? unclear) // // However, we want to drop as many privs as possible, hence: gid_t egid = getegid(); // documented to never fail, hence should return AID_CLAT == 1029 uid_t euid = geteuid(); // (ditto) setresgid(egid, egid, egid); // ignore any failure setresuid(euid, euid, euid); // ignore any failure // ideally we'd somehow drop supplementary groups too... // but for historical reasons that actually requires CAP_SETGID which we don't have // (see man 2 setgroups) // // Now we (should) have: // $ adb shell ps | grep clat // clat 5370 1479 10785364 2528 do_sys_poll 0 S clatd-wlan0 // # adb shell cat /proc/5370/status | egrep -i '^(Uid:|Gid:|Groups:)' // Uid: 1029 1029 1029 1029 // Gid: 1029 1029 1029 1029 // Groups: 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1018 1021 1023 1024 1032 1065 3001 3002 3003 3005 3006 3007 3009 3010 3011 3012 while ((opt = getopt(argc, argv, "i:p:4:6:t:r:w:h")) != -1) { switch (opt) { case 'i': uplink_interface = optarg; break; case 'p': plat_prefix = optarg; break; case '4': v4_addr = optarg; break; case '6': v6_addr = optarg; break; case 't': tunfd_str = optarg; break; case 'r': read_sock_str = optarg; break; case 'w': write_sock_str = optarg; break; case 'h': print_help(); exit(0); default: logmsg(ANDROID_LOG_FATAL, "Unknown option -%c. Exiting.", (char)optopt); exit(1); } } if (uplink_interface == NULL) { logmsg(ANDROID_LOG_FATAL, "clatd called without an interface"); exit(1); } if (tunfd_str != NULL && !parse_int(tunfd_str, &tunnel.fd4)) { logmsg(ANDROID_LOG_FATAL, "invalid tunfd %s", tunfd_str); exit(1); } if (!tunnel.fd4) { logmsg(ANDROID_LOG_FATAL, "no tunfd specified on commandline."); exit(1); } if (read_sock_str != NULL && !parse_int(read_sock_str, &tunnel.read_fd6)) { logmsg(ANDROID_LOG_FATAL, "invalid read socket %s", read_sock_str); exit(1); } if (!tunnel.read_fd6) { logmsg(ANDROID_LOG_FATAL, "no read_fd6 specified on commandline."); exit(1); } if (write_sock_str != NULL && !parse_int(write_sock_str, &tunnel.write_fd6)) { logmsg(ANDROID_LOG_FATAL, "invalid write socket %s", write_sock_str); exit(1); } if (!tunnel.write_fd6) { logmsg(ANDROID_LOG_FATAL, "no write_fd6 specified on commandline."); exit(1); } len = snprintf(tunnel.device4, sizeof(tunnel.device4), "%s%s", DEVICEPREFIX, uplink_interface); if (len >= sizeof(tunnel.device4)) { logmsg(ANDROID_LOG_FATAL, "interface name too long '%s'", tunnel.device4); exit(1); } Global_Clatd_Config.native_ipv6_interface = uplink_interface; if (!plat_prefix || inet_pton(AF_INET6, plat_prefix, &Global_Clatd_Config.plat_subnet) <= 0) { logmsg(ANDROID_LOG_FATAL, "invalid IPv6 address specified for plat prefix: %s", plat_prefix); exit(1); } if (!v4_addr || !inet_pton(AF_INET, v4_addr, &Global_Clatd_Config.ipv4_local_subnet.s_addr)) { logmsg(ANDROID_LOG_FATAL, "Invalid IPv4 address %s", v4_addr); exit(1); } if (!v6_addr || !inet_pton(AF_INET6, v6_addr, &Global_Clatd_Config.ipv6_local_subnet)) { logmsg(ANDROID_LOG_FATAL, "Invalid source address %s", v6_addr); exit(1); } logmsg(ANDROID_LOG_INFO, "Starting clat version " CLATD_VERSION " on %s plat=%s v4=%s v6=%s", uplink_interface, plat_prefix ? plat_prefix : "(none)", v4_addr ? v4_addr : "(none)", v6_addr ? v6_addr : "(none)"); { // Compile time detection of 32 vs 64-bit build. (note: C does not have 'constexpr') // Avoid use of preprocessor macros to get compile time syntax checking even on 64-bit. const int user_bits = sizeof(void*) * 8; const bool user32 = (user_bits == 32); // Note that on 64-bit all this personality related code simply compile optimizes out. // 32-bit: fetch current personality (see 'man personality': 0xFFFFFFFF means retrieve only) // On Linux fetching personality cannot fail. const int prev_personality = user32 ? personality(0xFFFFFFFFuL) : PER_LINUX; // 32-bit: attempt to get rid of kernel spoofing of 'uts.machine' architecture, // In theory this cannot fail, as PER_LINUX should always be supported. if (user32) (void)personality((prev_personality & ~PER_MASK) | PER_LINUX); // 64-bit: this will compile time evaluate to false. const bool was_linux32 = (prev_personality & PER_MASK) == PER_LINUX32; struct utsname uts = {}; if (uname(&uts)) exit(1); // only possible error is EFAULT, but 'uts' is on stack // sysname is likely 'Linux', release is 'kver', machine is kernel's *true* architecture logmsg(ANDROID_LOG_INFO, "%d-bit userspace on %s kernel %s for %s%s.", user_bits, uts.sysname, uts.release, uts.machine, was_linux32 ? " (was spoofed)" : ""); // 32-bit: try to return to the 'default' personality // In theory this cannot fail, because it was already previously in use. if (user32) (void)personality(prev_personality); } // Loop until someone sends us a signal or brings down the tun interface. if (signal(SIGTERM, handle_sigterm) == SIG_ERR) { logmsg(ANDROID_LOG_FATAL, "sigterm handler failed: %s", strerror(errno)); exit(1); } // Apparently some network gear will refuse to perform NS for IPs that aren't DAD'ed, // this would then result in an ipv6-only network with working native ipv6, working // IPv4 via DNS64, but non-functioning IPv4 via CLAT (ie. IPv4 literals + IPv4 only apps). // The kernel itself doesn't do DAD for anycast ips (but does handle IPV6 MLD and handle ND). // So we'll spoof dad here, and yeah, we really should check for a response and in // case of failure pick a different IP. Seeing as 48-bits of the IP are utterly random // (with the other 16 chosen to guarantee checksum neutrality) this seems like a remote // concern... // TODO: actually perform true DAD send_dad(tunnel.write_fd6, &Global_Clatd_Config.ipv6_local_subnet); enable_seccomp(); // WARNING: from this point forward very limited system calls available. event_loop(&tunnel); if (sigterm) { logmsg(ANDROID_LOG_INFO, "Shutting down clatd on %s, already received SIGTERM", uplink_interface); } else { // this implies running == false, ie. we received EOF or ENETDOWN error. logmsg(ANDROID_LOG_INFO, "Shutting down clatd on %s, waiting for SIGTERM", uplink_interface); // let's give higher level java code 15 seconds to kill us, // but eventually terminate anyway, in case system server forgets about us... // sleep() should be interrupted by SIGTERM, the handler should set 'sigterm' sleep(15); logmsg(ANDROID_LOG_INFO, "Clatd on %s %s SIGTERM", uplink_interface, sigterm ? "received" : "timed out waiting for"); } // Using _exit() here avoids 4 mprotect() syscalls triggered via 'exit(0)' or 'return 0' _exit(0); }