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Sources/procd/trace/trace.c

  1 /*
  2  * Copyright (C) 2015 John Crispin <blogic@openwrt.org>
  3  *
  4  * This program is free software; you can redistribute it and/or modify
  5  * it under the terms of the GNU Lesser General Public License version 2.1
  6  * as published by the Free Software Foundation
  7  *
  8  * This program is distributed in the hope that it will be useful,
  9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 11  * GNU General Public License for more details.
 12  */
 13 
 14 #define _GNU_SOURCE
 15 #include <fcntl.h>
 16 #include <stddef.h>
 17 #include <sys/ptrace.h>
 18 #include <sys/stat.h>
 19 #include <sys/types.h>
 20 #include <sys/user.h>
 21 #include <sys/wait.h>
 22 #include <unistd.h>
 23 #include <stdlib.h>
 24 #include <stdio.h>
 25 #include <errno.h>
 26 #include <string.h>
 27 #include <syslog.h>
 28 #include <limits.h>
 29 
 30 #ifndef PTRACE_EVENT_STOP
 31 /* PTRACE_EVENT_STOP is defined in linux/ptrace.h, but this header
 32  * collides with musl's sys/ptrace.h */
 33 #define PTRACE_EVENT_STOP 128
 34 #endif
 35 
 36 #ifndef PTRACE_EVENT_SECCOMP
 37 /* undefined with uClibc-ng */
 38 #define PTRACE_EVENT_SECCOMP 7
 39 #endif
 40 
 41 #include <libubox/ulog.h>
 42 #include <libubox/uloop.h>
 43 #include <libubox/blobmsg.h>
 44 #include <libubox/blobmsg_json.h>
 45 
 46 #include "../syscall-names.h"
 47 
 48 #define _offsetof(a, b) __builtin_offsetof(a,b)
 49 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 50 
 51 #if defined (__aarch64__)
 52 #include <linux/ptrace.h>
 53 #elif defined(__amd64__)
 54 #define reg_syscall_nr  _offsetof(struct user, regs.orig_rax)
 55 #elif defined(__arm__)
 56 #include <asm/ptrace.h>         /* for PTRACE_SET_SYSCALL */
 57 #define reg_syscall_nr  _offsetof(struct user, regs.uregs[7])
 58 # if defined(__ARM_EABI__)
 59 # define reg_retval_nr  _offsetof(struct user, regs.uregs[0])
 60 # endif
 61 #elif defined(__i386__)
 62 #define reg_syscall_nr  _offsetof(struct user, regs.orig_eax)
 63 #elif defined(__mips)
 64 # ifndef EF_REG2
 65 # define EF_REG2        8
 66 # endif
 67 #define reg_syscall_nr  (EF_REG2 / 4)
 68 #elif defined(__PPC__)
 69 #define reg_syscall_nr  _offsetof(struct user, regs.gpr[0])
 70 #define reg_retval_nr   _offsetof(struct user, regs.gpr[3])
 71 #else
 72 #error tracing is not supported on this architecture
 73 #endif
 74 
 75 enum mode {
 76         UTRACE,
 77         SECCOMP_TRACE,
 78 } mode = UTRACE;
 79 
 80 struct tracee {
 81         struct uloop_process proc;
 82         int in_syscall;
 83 };
 84 
 85 static struct tracee tracer;
 86 static int syscall_count[SYSCALL_COUNT];
 87 static int violation_count;
 88 static struct blob_buf b;
 89 static int debug;
 90 char *json = NULL;
 91 int ptrace_restart;
 92 
 93 static void set_syscall(const char *name, int val)
 94 {
 95         int i;
 96 
 97         for (i = 0; i < SYSCALL_COUNT; i++) {
 98                 int sc = syscall_index_to_number(i);
 99                 if (syscall_name(sc) && !strcmp(syscall_name(sc), name)) {
100                         syscall_count[i] = val;
101                         return;
102                 }
103         }
104 }
105 
106 struct syscall {
107         int syscall;
108         int count;
109 };
110 
111 static int cmp_count(const void *a, const void *b)
112 {
113         return ((struct syscall*)b)->count - ((struct syscall*)a)->count;
114 }
115 
116 static void print_syscalls(int policy, const char *json)
117 {
118         void *c, *d, *e;
119         int i;
120         char *tmp;
121 
122         if (mode == UTRACE) {
123                 set_syscall("rt_sigaction", 1);
124                 set_syscall("sigreturn", 1);
125                 set_syscall("rt_sigreturn", 1);
126                 set_syscall("exit_group", 1);
127                 set_syscall("exit", 1);
128         }
129 
130         struct syscall sorted[SYSCALL_COUNT];
131 
132         for (i = 0; i < SYSCALL_COUNT; i++) {
133                 sorted[i].syscall = syscall_index_to_number(i);
134                 sorted[i].count = syscall_count[i];
135         }
136 
137         qsort(sorted, SYSCALL_COUNT, sizeof(sorted[0]), cmp_count);
138 
139         blob_buf_init(&b, 0);
140         blobmsg_add_string(&b, "defaultAction", "SCMP_ACT_KILL_PROCESS");
141         c = blobmsg_open_array(&b, "syscalls");
142         d = blobmsg_open_table(&b, "");
143         e = blobmsg_open_array(&b, "names");
144 
145         for (i = 0; i < SYSCALL_COUNT; i++) {
146                 int sc = sorted[i].syscall;
147                 if (!sorted[i].count)
148                         break;
149                 if (syscall_name(sc)) {
150                         if (debug)
151                                 printf("syscall %d (%s) was called %d times\n",
152                                        sc, syscall_name(sc), sorted[i].count);
153                         blobmsg_add_string(&b, NULL, syscall_name(sc));
154                 } else {
155                         ULOG_ERR("no name found for syscall(%d)\n", sc);
156                 }
157         }
158         blobmsg_close_array(&b, e);
159         blobmsg_add_string(&b, "action", "SCMP_ACT_ALLOW");
160         blobmsg_close_table(&b, d);
161         blobmsg_close_array(&b, c);
162         if (json) {
163                 FILE *fp = fopen(json, "w");
164                 if (fp) {
165                         tmp = blobmsg_format_json_indent(b.head, true, 0);
166                         if (!tmp) {
167                                 fclose(fp);
168                                 return;
169                         }
170 
171                         fprintf(fp, "%s\n", tmp);
172                         free(tmp);
173                         fclose(fp);
174                         ULOG_INFO("saving syscall trace to %s\n", json);
175                 } else {
176                         ULOG_ERR("failed to open %s\n", json);
177                 }
178         } else {
179                 tmp = blobmsg_format_json_indent(b.head, true, 0);
180                 if (!tmp)
181                         return;
182 
183                 printf("%s\n", tmp);
184                 free(tmp);
185         }
186 }
187 
188 static void report_seccomp_vialation(pid_t pid, unsigned syscall)
189 {
190         char buf[200];
191         snprintf(buf, sizeof(buf), "/proc/%d/cmdline", pid);
192         int f = open(buf, O_RDONLY);
193         if (f < 0)
194                 return;
195 
196         int r = read(f, buf, sizeof(buf) - 1);
197         buf[sizeof(buf) - 1] = '\0';
198 
199         if (r >= 0)
200                 buf[r] = 0;
201         else
202                 strcpy(buf, "unknown?");
203         close(f);
204 
205         if (violation_count < INT_MAX)
206                 violation_count++;
207         int i = syscall_index(syscall);
208         if (i >= 0) {
209                 syscall_count[i]++;
210                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %s (see %s)\n",
211                          buf, pid,  syscall_name(syscall), json);
212         } else {
213                 ULOG_ERR("%s[%u] tried to call non-whitelisted syscall: %d (see %s)\n",
214                          buf, pid,  syscall, json);
215         }
216 }
217 
218 static void tracer_cb(struct uloop_process *c, int ret)
219 {
220         struct tracee *tracee = container_of(c, struct tracee, proc);
221         int inject_signal = 0;
222 
223         /* We explicitely check for events in upper 16 bits, because
224          * musl (as opposed to glibc) does not report
225          * PTRACE_EVENT_STOP as WIFSTOPPED */
226         if (WIFSTOPPED(ret) || (ret >> 16)) {
227                 if (WSTOPSIG(ret) & 0x80) {
228                         if (!tracee->in_syscall) {
229 #ifdef __aarch64__
230                                 int syscall = -1;
231                                 struct ptrace_syscall_info ptsi = {.op=PTRACE_SYSCALL_INFO_ENTRY};
232                                 if (ptrace(PTRACE_GET_SYSCALL_INFO, c->pid, sizeof(ptsi), &ptsi) != -1)
233                                         syscall = ptsi.entry.nr;
234 #else
235                                 int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
236 #endif
237                                 int i = syscall_index(syscall);
238                                 if (i >= 0) {
239                                         syscall_count[i]++;
240                                         if (debug)
241                                                 fprintf(stderr, "%s()\n", syscall_name(syscall));
242                                 } else if (debug) {
243                                         fprintf(stderr, "syscal(%d)\n", syscall);
244                                 }
245                         }
246                         tracee->in_syscall = !tracee->in_syscall;
247                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_FORK << 8)) ||
248                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_VFORK << 8)) ||
249                            (ret >> 8) == (SIGTRAP | (PTRACE_EVENT_CLONE << 8))) {
250                         struct tracee *child = calloc(1, sizeof(struct tracee));
251 
252                         unsigned long msg;
253                         ptrace(PTRACE_GETEVENTMSG, c->pid, 0, &msg);
254                         child->proc.pid = msg;
255                         child->proc.cb = tracer_cb;
256                         ptrace(ptrace_restart, child->proc.pid, 0, 0);
257                         uloop_process_add(&child->proc);
258                         if (debug)
259                                 fprintf(stderr, "Tracing new child %d\n", child->proc.pid);
260                 } else if ((ret >> 16) == PTRACE_EVENT_STOP) {
261                         /* Nothing special to do here */
262                 } else if ((ret >> 8) == (SIGTRAP | (PTRACE_EVENT_SECCOMP << 8))) {
263 #ifdef __aarch64__
264                         int syscall = -1;
265                         struct ptrace_syscall_info ptsi = {.op=PTRACE_SYSCALL_INFO_SECCOMP};
266                         if (ptrace(PTRACE_GET_SYSCALL_INFO, c->pid, sizeof(ptsi), &ptsi) != -1)
267                                 syscall = ptsi.entry.nr;
268 #else
269                         int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
270 #if defined(__arm__)
271                         ptrace(PTRACE_SET_SYSCALL, c->pid, 0, -1);
272                         ptrace(PTRACE_POKEUSER, c->pid, reg_retval_nr, -ENOSYS);
273 #else
274                         ptrace(PTRACE_POKEUSER, c->pid, reg_syscall_nr, -1);
275 #endif
276 #endif
277                         report_seccomp_vialation(c->pid, syscall);
278                 } else {
279                         inject_signal = WSTOPSIG(ret);
280                         if (debug)
281                                 fprintf(stderr, "Injecting signal %d into pid %d\n",
282                                         inject_signal, tracee->proc.pid);
283                 }
284         } else if (WIFEXITED(ret) || (WIFSIGNALED(ret) && WTERMSIG(ret))) {
285                 if (tracee == &tracer) {
286                         uloop_end(); /* Main process exit */
287                 } else {
288                         if (debug)
289                                 fprintf(stderr, "Child %d exited\n", tracee->proc.pid);
290                         free(tracee);
291                 }
292                 return;
293         }
294 
295         ptrace(ptrace_restart, c->pid, 0, inject_signal);
296         uloop_process_add(c);
297 }
298 
299 static void sigterm_handler(int signum)
300 {
301         /* When we receive SIGTERM, we forward it to the tracee. After
302          * the tracee exits, trace_cb() will be called and make us
303          * exit too. */
304         kill(tracer.proc.pid, SIGTERM);
305 }
306 
307 
308 int main(int argc, char **argv, char **envp)
309 {
310         int status, ch, policy = EPERM;
311         pid_t child;
312 
313         /* When invoked via seccomp-trace symlink, work as seccomp
314          * violation logger rather than as syscall tracer */
315         if (strstr(argv[0], "seccomp-trace"))
316                 mode = SECCOMP_TRACE;
317 
318         while ((ch = getopt(argc, argv, "f:p:")) != -1) {
319                 switch (ch) {
320                 case 'f':
321                         json = optarg;
322                         break;
323                 case 'p':
324                         policy = atoi(optarg);
325                         break;
326                 }
327         }
328 
329         if (!json)
330                 json = getenv("SECCOMP_FILE");
331 
332         argc -= optind;
333         argv += optind;
334 
335         if (!argc)
336                 return -1;
337 
338         if (getenv("TRACE_DEBUG"))
339                 debug = 1;
340         unsetenv("TRACE_DEBUG");
341 
342         child = fork();
343 
344         if (child == 0) {
345                 char **_argv = calloc(argc + 1, sizeof(char *));
346                 char **_envp;
347                 char *preload = NULL;
348                 const char *old_preload = getenv("LD_PRELOAD");
349                 int newenv = 0;
350                 int envc = 0;
351                 int ret;
352 
353                 memcpy(_argv, argv, argc * sizeof(char *));
354 
355                 while (envp[envc++])
356                         ;
357 
358                 _envp = calloc(envc + 2, sizeof(char *));
359                 switch (mode) {
360                 case UTRACE:
361                         preload = "/lib/libpreload-trace.so";
362                         newenv = 1;
363                         break;
364                 case SECCOMP_TRACE:
365                         preload = "/lib/libpreload-seccomp.so";
366                         newenv = 2;
367                         if (asprintf(&_envp[1], "SECCOMP_FILE=%s", json ? json : "") < 0)
368                                 ULOG_ERR("failed to allocate SECCOMP_FILE env: %m\n");
369 
370                         kill(getpid(), SIGSTOP);
371                         break;
372                 }
373                 if (asprintf(&_envp[0], "LD_PRELOAD=%s%s%s", preload,
374                              old_preload ? ":" : "",
375                               old_preload ? old_preload : "") < 0)
376                         ULOG_ERR("failed to allocate LD_PRELOAD env: %m\n");
377 
378                 memcpy(&_envp[newenv], envp, envc * sizeof(char *));
379 
380                 ret = execve(_argv[0], _argv, _envp);
381                 ULOG_ERR("failed to exec %s: %m\n", _argv[0]);
382 
383                 free(_argv);
384                 if (_envp[0])
385                         free(_envp[0]);
386                 if (newenv == 2 && _envp[1])
387                         free(_envp[1]);
388                 free(_envp);
389                 return ret;
390         }
391 
392         if (child < 0)
393                 return -1;
394 
395         waitpid(child, &status, WUNTRACED);
396         if (!WIFSTOPPED(status)) {
397                 ULOG_ERR("failed to start %s\n", *argv);
398                 return -1;
399         }
400 
401         /* Initialize uloop to catch all ptrace stops from now on. */
402         uloop_init();
403 
404         int ptrace_options = PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK | PTRACE_O_TRACECLONE;
405         switch (mode) {
406         case UTRACE:
407                 ptrace_options |= PTRACE_O_TRACESYSGOOD;
408                 ptrace_restart = PTRACE_SYSCALL;
409                 break;
410         case SECCOMP_TRACE:
411                 ptrace_options |= PTRACE_O_TRACESECCOMP;
412                 ptrace_restart = PTRACE_CONT;
413                 break;
414         }
415         if (ptrace(PTRACE_SEIZE, child, 0, ptrace_options) == -1) {
416                 ULOG_ERR("PTRACE_SEIZE: %m\n");
417                 return -1;
418         }
419         if (ptrace(ptrace_restart, child, 0, SIGCONT) == -1) {
420                 ULOG_ERR("ptrace_restart: %m\n");
421                 return -1;
422         }
423 
424         tracer.proc.pid = child;
425         tracer.proc.cb = tracer_cb;
426         uloop_process_add(&tracer.proc);
427         signal(SIGTERM, sigterm_handler); /* Override uloop's SIGTERM handler */
428         uloop_run();
429         uloop_done();
430 
431 
432         switch (mode) {
433         case UTRACE:
434                 if (!json)
435                         if (asprintf(&json, "/tmp/%s.%u.json", basename(*argv), child) < 0)
436                                 ULOG_ERR("failed to allocate output path: %m\n");
437                 break;
438         case SECCOMP_TRACE:
439                 if (!violation_count)
440                         return 0;
441                 if (asprintf(&json, "/tmp/%s.%u.violations.json", basename(*argv), child) < 0)
442                         ULOG_ERR("failed to allocate violations output path: %m\n");
443                 break;
444         }
445         print_syscalls(policy, json);
446         return 0;
447 }
448 

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