1 /* 2 * linux/kernel/seccomp.c 3 * 4 * Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com> 5 * 6 * Copyright (C) 2012 Google, Inc. 7 * Will Drewry <wad@chromium.org> 8 * 9 * This defines a simple but solid secure-computing facility. 10 * 11 * Mode 1 uses a fixed list of allowed system calls. 12 * Mode 2 allows user-defined system call filters in the form 13 * of Berkeley Packet Filters/Linux Socket Filters. 14 */ 15 16 #include <linux/refcount.h> 17 #include <linux/audit.h> 18 #include <linux/compat.h> 19 #include <linux/coredump.h> 20 #include <linux/kmemleak.h> 21 #include <linux/sched.h> 22 #include <linux/sched/task_stack.h> 23 #include <linux/seccomp.h> 24 #include <linux/slab.h> 25 #include <linux/syscalls.h> 26 #include <linux/sysctl.h> 27 28 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER 29 #include <asm/syscall.h> 30 #endif 31 32 #ifdef CONFIG_SECCOMP_FILTER 33 #include <linux/filter.h> 34 #include <linux/pid.h> 35 #include <linux/ptrace.h> 36 #include <linux/security.h> 37 #include <linux/tracehook.h> 38 #include <linux/uaccess.h> 39 40 /** 41 * struct seccomp_filter - container for seccomp BPF programs 42 * 43 * @usage: reference count to manage the object lifetime. 44 * get/put helpers should be used when accessing an instance 45 * outside of a lifetime-guarded section. In general, this 46 * is only needed for handling filters shared across tasks. 47 * @log: true if all actions except for SECCOMP_RET_ALLOW should be logged 48 * @prev: points to a previously installed, or inherited, filter 49 * @prog: the BPF program to evaluate 50 * 51 * seccomp_filter objects are organized in a tree linked via the @prev 52 * pointer. For any task, it appears to be a singly-linked list starting 53 * with current->seccomp.filter, the most recently attached or inherited filter. 54 * However, multiple filters may share a @prev node, by way of fork(), which 55 * results in a unidirectional tree existing in memory. This is similar to 56 * how namespaces work. 57 * 58 * seccomp_filter objects should never be modified after being attached 59 * to a task_struct (other than @usage). 60 */ 61 struct seccomp_filter { 62 refcount_t usage; 63 bool log; 64 struct seccomp_filter *prev; 65 struct bpf_prog *prog; 66 }; 67 68 /* Limit any path through the tree to 256KB worth of instructions. */ 69 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter)) 70 71 /* 72 * Endianness is explicitly ignored and left for BPF program authors to manage 73 * as per the specific architecture. 74 */ 75 static void populate_seccomp_data(struct seccomp_data *sd) 76 { 77 struct task_struct *task = current; 78 struct pt_regs *regs = task_pt_regs(task); 79 unsigned long args[6]; 80 81 sd->nr = syscall_get_nr(task, regs); 82 sd->arch = syscall_get_arch(); 83 syscall_get_arguments(task, regs, 0, 6, args); 84 sd->args[0] = args[0]; 85 sd->args[1] = args[1]; 86 sd->args[2] = args[2]; 87 sd->args[3] = args[3]; 88 sd->args[4] = args[4]; 89 sd->args[5] = args[5]; 90 sd->instruction_pointer = KSTK_EIP(task); 91 } 92 93 /** 94 * seccomp_check_filter - verify seccomp filter code 95 * @filter: filter to verify 96 * @flen: length of filter 97 * 98 * Takes a previously checked filter (by bpf_check_classic) and 99 * redirects all filter code that loads struct sk_buff data 100 * and related data through seccomp_bpf_load. It also 101 * enforces length and alignment checking of those loads. 102 * 103 * Returns 0 if the rule set is legal or -EINVAL if not. 104 */ 105 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) 106 { 107 int pc; 108 for (pc = 0; pc < flen; pc++) { 109 struct sock_filter *ftest = &filter[pc]; 110 u16 code = ftest->code; 111 u32 k = ftest->k; 112 113 switch (code) { 114 case BPF_LD | BPF_W | BPF_ABS: 115 ftest->code = BPF_LDX | BPF_W | BPF_ABS; 116 /* 32-bit aligned and not out of bounds. */ 117 if (k >= sizeof(struct seccomp_data) || k & 3) 118 return -EINVAL; 119 continue; 120 case BPF_LD | BPF_W | BPF_LEN: 121 ftest->code = BPF_LD | BPF_IMM; 122 ftest->k = sizeof(struct seccomp_data); 123 continue; 124 case BPF_LDX | BPF_W | BPF_LEN: 125 ftest->code = BPF_LDX | BPF_IMM; 126 ftest->k = sizeof(struct seccomp_data); 127 continue; 128 /* Explicitly include allowed calls. */ 129 case BPF_RET | BPF_K: 130 case BPF_RET | BPF_A: 131 case BPF_ALU | BPF_ADD | BPF_K: 132 case BPF_ALU | BPF_ADD | BPF_X: 133 case BPF_ALU | BPF_SUB | BPF_K: 134 case BPF_ALU | BPF_SUB | BPF_X: 135 case BPF_ALU | BPF_MUL | BPF_K: 136 case BPF_ALU | BPF_MUL | BPF_X: 137 case BPF_ALU | BPF_DIV | BPF_K: 138 case BPF_ALU | BPF_DIV | BPF_X: 139 case BPF_ALU | BPF_AND | BPF_K: 140 case BPF_ALU | BPF_AND | BPF_X: 141 case BPF_ALU | BPF_OR | BPF_K: 142 case BPF_ALU | BPF_OR | BPF_X: 143 case BPF_ALU | BPF_XOR | BPF_K: 144 case BPF_ALU | BPF_XOR | BPF_X: 145 case BPF_ALU | BPF_LSH | BPF_K: 146 case BPF_ALU | BPF_LSH | BPF_X: 147 case BPF_ALU | BPF_RSH | BPF_K: 148 case BPF_ALU | BPF_RSH | BPF_X: 149 case BPF_ALU | BPF_NEG: 150 case BPF_LD | BPF_IMM: 151 case BPF_LDX | BPF_IMM: 152 case BPF_MISC | BPF_TAX: 153 case BPF_MISC | BPF_TXA: 154 case BPF_LD | BPF_MEM: 155 case BPF_LDX | BPF_MEM: 156 case BPF_ST: 157 case BPF_STX: 158 case BPF_JMP | BPF_JA: 159 case BPF_JMP | BPF_JEQ | BPF_K: 160 case BPF_JMP | BPF_JEQ | BPF_X: 161 case BPF_JMP | BPF_JGE | BPF_K: 162 case BPF_JMP | BPF_JGE | BPF_X: 163 case BPF_JMP | BPF_JGT | BPF_K: 164 case BPF_JMP | BPF_JGT | BPF_X: 165 case BPF_JMP | BPF_JSET | BPF_K: 166 case BPF_JMP | BPF_JSET | BPF_X: 167 continue; 168 default: 169 return -EINVAL; 170 } 171 } 172 return 0; 173 } 174 175 /** 176 * seccomp_run_filters - evaluates all seccomp filters against @sd 177 * @sd: optional seccomp data to be passed to filters 178 * @match: stores struct seccomp_filter that resulted in the return value, 179 * unless filter returned SECCOMP_RET_ALLOW, in which case it will 180 * be unchanged. 181 * 182 * Returns valid seccomp BPF response codes. 183 */ 184 #define ACTION_ONLY(ret) ((s32)((ret) & (SECCOMP_RET_ACTION_FULL))) 185 static u32 seccomp_run_filters(const struct seccomp_data *sd, 186 struct seccomp_filter **match) 187 { 188 struct seccomp_data sd_local; 189 u32 ret = SECCOMP_RET_ALLOW; 190 /* Make sure cross-thread synced filter points somewhere sane. */ 191 struct seccomp_filter *f = 192 lockless_dereference(current->seccomp.filter); 193 194 /* Ensure unexpected behavior doesn't result in failing open. */ 195 if (unlikely(WARN_ON(f == NULL))) 196 return SECCOMP_RET_KILL_PROCESS; 197 198 if (!sd) { 199 populate_seccomp_data(&sd_local); 200 sd = &sd_local; 201 } 202 203 /* 204 * All filters in the list are evaluated and the lowest BPF return 205 * value always takes priority (ignoring the DATA). 206 */ 207 for (; f; f = f->prev) { 208 u32 cur_ret = BPF_PROG_RUN(f->prog, sd); 209 210 if (ACTION_ONLY(cur_ret) < ACTION_ONLY(ret)) { 211 ret = cur_ret; 212 *match = f; 213 } 214 } 215 return ret; 216 } 217 #endif /* CONFIG_SECCOMP_FILTER */ 218 219 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 220 { 221 assert_spin_locked(¤t->sighand->siglock); 222 223 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) 224 return false; 225 226 return true; 227 } 228 229 static inline void seccomp_assign_mode(struct task_struct *task, 230 unsigned long seccomp_mode) 231 { 232 assert_spin_locked(&task->sighand->siglock); 233 234 task->seccomp.mode = seccomp_mode; 235 /* 236 * Make sure TIF_SECCOMP cannot be set before the mode (and 237 * filter) is set. 238 */ 239 smp_mb__before_atomic(); 240 set_tsk_thread_flag(task, TIF_SECCOMP); 241 } 242 243 #ifdef CONFIG_SECCOMP_FILTER 244 /* Returns 1 if the parent is an ancestor of the child. */ 245 static int is_ancestor(struct seccomp_filter *parent, 246 struct seccomp_filter *child) 247 { 248 /* NULL is the root ancestor. */ 249 if (parent == NULL) 250 return 1; 251 for (; child; child = child->prev) 252 if (child == parent) 253 return 1; 254 return 0; 255 } 256 257 /** 258 * seccomp_can_sync_threads: checks if all threads can be synchronized 259 * 260 * Expects sighand and cred_guard_mutex locks to be held. 261 * 262 * Returns 0 on success, -ve on error, or the pid of a thread which was 263 * either not in the correct seccomp mode or it did not have an ancestral 264 * seccomp filter. 265 */ 266 static inline pid_t seccomp_can_sync_threads(void) 267 { 268 struct task_struct *thread, *caller; 269 270 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 271 assert_spin_locked(¤t->sighand->siglock); 272 273 /* Validate all threads being eligible for synchronization. */ 274 caller = current; 275 for_each_thread(caller, thread) { 276 pid_t failed; 277 278 /* Skip current, since it is initiating the sync. */ 279 if (thread == caller) 280 continue; 281 282 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || 283 (thread->seccomp.mode == SECCOMP_MODE_FILTER && 284 is_ancestor(thread->seccomp.filter, 285 caller->seccomp.filter))) 286 continue; 287 288 /* Return the first thread that cannot be synchronized. */ 289 failed = task_pid_vnr(thread); 290 /* If the pid cannot be resolved, then return -ESRCH */ 291 if (unlikely(WARN_ON(failed == 0))) 292 failed = -ESRCH; 293 return failed; 294 } 295 296 return 0; 297 } 298 299 /** 300 * seccomp_sync_threads: sets all threads to use current's filter 301 * 302 * Expects sighand and cred_guard_mutex locks to be held, and for 303 * seccomp_can_sync_threads() to have returned success already 304 * without dropping the locks. 305 * 306 */ 307 static inline void seccomp_sync_threads(void) 308 { 309 struct task_struct *thread, *caller; 310 311 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 312 assert_spin_locked(¤t->sighand->siglock); 313 314 /* Synchronize all threads. */ 315 caller = current; 316 for_each_thread(caller, thread) { 317 /* Skip current, since it needs no changes. */ 318 if (thread == caller) 319 continue; 320 321 /* Get a task reference for the new leaf node. */ 322 get_seccomp_filter(caller); 323 /* 324 * Drop the task reference to the shared ancestor since 325 * current's path will hold a reference. (This also 326 * allows a put before the assignment.) 327 */ 328 put_seccomp_filter(thread); 329 smp_store_release(&thread->seccomp.filter, 330 caller->seccomp.filter); 331 332 /* 333 * Don't let an unprivileged task work around 334 * the no_new_privs restriction by creating 335 * a thread that sets it up, enters seccomp, 336 * then dies. 337 */ 338 if (task_no_new_privs(caller)) 339 task_set_no_new_privs(thread); 340 341 /* 342 * Opt the other thread into seccomp if needed. 343 * As threads are considered to be trust-realm 344 * equivalent (see ptrace_may_access), it is safe to 345 * allow one thread to transition the other. 346 */ 347 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) 348 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 349 } 350 } 351 352 /** 353 * seccomp_prepare_filter: Prepares a seccomp filter for use. 354 * @fprog: BPF program to install 355 * 356 * Returns filter on success or an ERR_PTR on failure. 357 */ 358 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 359 { 360 struct seccomp_filter *sfilter; 361 int ret; 362 const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE); 363 364 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 365 return ERR_PTR(-EINVAL); 366 367 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 368 369 /* 370 * Installing a seccomp filter requires that the task has 371 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 372 * This avoids scenarios where unprivileged tasks can affect the 373 * behavior of privileged children. 374 */ 375 if (!task_no_new_privs(current) && 376 security_capable_noaudit(current_cred(), current_user_ns(), 377 CAP_SYS_ADMIN) != 0) 378 return ERR_PTR(-EACCES); 379 380 /* Allocate a new seccomp_filter */ 381 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); 382 if (!sfilter) 383 return ERR_PTR(-ENOMEM); 384 385 ret = bpf_prog_create_from_user(&sfilter->prog, fprog, 386 seccomp_check_filter, save_orig); 387 if (ret < 0) { 388 kfree(sfilter); 389 return ERR_PTR(ret); 390 } 391 392 refcount_set(&sfilter->usage, 1); 393 394 return sfilter; 395 } 396 397 /** 398 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 399 * @user_filter: pointer to the user data containing a sock_fprog. 400 * 401 * Returns 0 on success and non-zero otherwise. 402 */ 403 static struct seccomp_filter * 404 seccomp_prepare_user_filter(const char __user *user_filter) 405 { 406 struct sock_fprog fprog; 407 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 408 409 #ifdef CONFIG_COMPAT 410 if (in_compat_syscall()) { 411 struct compat_sock_fprog fprog32; 412 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 413 goto out; 414 fprog.len = fprog32.len; 415 fprog.filter = compat_ptr(fprog32.filter); 416 } else /* falls through to the if below. */ 417 #endif 418 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 419 goto out; 420 filter = seccomp_prepare_filter(&fprog); 421 out: 422 return filter; 423 } 424 425 /** 426 * seccomp_attach_filter: validate and attach filter 427 * @flags: flags to change filter behavior 428 * @filter: seccomp filter to add to the current process 429 * 430 * Caller must be holding current->sighand->siglock lock. 431 * 432 * Returns 0 on success, -ve on error. 433 */ 434 static long seccomp_attach_filter(unsigned int flags, 435 struct seccomp_filter *filter) 436 { 437 unsigned long total_insns; 438 struct seccomp_filter *walker; 439 440 assert_spin_locked(¤t->sighand->siglock); 441 442 /* Validate resulting filter length. */ 443 total_insns = filter->prog->len; 444 for (walker = current->seccomp.filter; walker; walker = walker->prev) 445 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 446 if (total_insns > MAX_INSNS_PER_PATH) 447 return -ENOMEM; 448 449 /* If thread sync has been requested, check that it is possible. */ 450 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 451 int ret; 452 453 ret = seccomp_can_sync_threads(); 454 if (ret) 455 return ret; 456 } 457 458 /* Set log flag, if present. */ 459 if (flags & SECCOMP_FILTER_FLAG_LOG) 460 filter->log = true; 461 462 /* 463 * If there is an existing filter, make it the prev and don't drop its 464 * task reference. 465 */ 466 filter->prev = current->seccomp.filter; 467 current->seccomp.filter = filter; 468 469 /* Now that the new filter is in place, synchronize to all threads. */ 470 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 471 seccomp_sync_threads(); 472 473 return 0; 474 } 475 476 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 477 void get_seccomp_filter(struct task_struct *tsk) 478 { 479 struct seccomp_filter *orig = tsk->seccomp.filter; 480 if (!orig) 481 return; 482 /* Reference count is bounded by the number of total processes. */ 483 refcount_inc(&orig->usage); 484 } 485 486 static inline void seccomp_filter_free(struct seccomp_filter *filter) 487 { 488 if (filter) { 489 bpf_prog_destroy(filter->prog); 490 kfree(filter); 491 } 492 } 493 494 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 495 void put_seccomp_filter(struct task_struct *tsk) 496 { 497 struct seccomp_filter *orig = tsk->seccomp.filter; 498 /* Clean up single-reference branches iteratively. */ 499 while (orig && refcount_dec_and_test(&orig->usage)) { 500 struct seccomp_filter *freeme = orig; 501 orig = orig->prev; 502 seccomp_filter_free(freeme); 503 } 504 } 505 506 static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason) 507 { 508 memset(info, 0, sizeof(*info)); 509 info->si_signo = SIGSYS; 510 info->si_code = SYS_SECCOMP; 511 info->si_call_addr = (void __user *)KSTK_EIP(current); 512 info->si_errno = reason; 513 info->si_arch = syscall_get_arch(); 514 info->si_syscall = syscall; 515 } 516 517 /** 518 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 519 * @syscall: syscall number to send to userland 520 * @reason: filter-supplied reason code to send to userland (via si_errno) 521 * 522 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 523 */ 524 static void seccomp_send_sigsys(int syscall, int reason) 525 { 526 struct siginfo info; 527 seccomp_init_siginfo(&info, syscall, reason); 528 force_sig_info(SIGSYS, &info, current); 529 } 530 #endif /* CONFIG_SECCOMP_FILTER */ 531 532 /* For use with seccomp_actions_logged */ 533 #define SECCOMP_LOG_KILL_PROCESS (1 << 0) 534 #define SECCOMP_LOG_KILL_THREAD (1 << 1) 535 #define SECCOMP_LOG_TRAP (1 << 2) 536 #define SECCOMP_LOG_ERRNO (1 << 3) 537 #define SECCOMP_LOG_TRACE (1 << 4) 538 #define SECCOMP_LOG_LOG (1 << 5) 539 #define SECCOMP_LOG_ALLOW (1 << 6) 540 541 static u32 seccomp_actions_logged = SECCOMP_LOG_KILL_PROCESS | 542 SECCOMP_LOG_KILL_THREAD | 543 SECCOMP_LOG_TRAP | 544 SECCOMP_LOG_ERRNO | 545 SECCOMP_LOG_TRACE | 546 SECCOMP_LOG_LOG; 547 548 static inline void seccomp_log(unsigned long syscall, long signr, u32 action, 549 bool requested) 550 { 551 bool log = false; 552 553 switch (action) { 554 case SECCOMP_RET_ALLOW: 555 break; 556 case SECCOMP_RET_TRAP: 557 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRAP; 558 break; 559 case SECCOMP_RET_ERRNO: 560 log = requested && seccomp_actions_logged & SECCOMP_LOG_ERRNO; 561 break; 562 case SECCOMP_RET_TRACE: 563 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRACE; 564 break; 565 case SECCOMP_RET_LOG: 566 log = seccomp_actions_logged & SECCOMP_LOG_LOG; 567 break; 568 case SECCOMP_RET_KILL_THREAD: 569 log = seccomp_actions_logged & SECCOMP_LOG_KILL_THREAD; 570 break; 571 case SECCOMP_RET_KILL_PROCESS: 572 default: 573 log = seccomp_actions_logged & SECCOMP_LOG_KILL_PROCESS; 574 } 575 576 /* 577 * Force an audit message to be emitted when the action is RET_KILL_*, 578 * RET_LOG, or the FILTER_FLAG_LOG bit was set and the action is 579 * allowed to be logged by the admin. 580 */ 581 if (log) 582 return __audit_seccomp(syscall, signr, action); 583 584 /* 585 * Let the audit subsystem decide if the action should be audited based 586 * on whether the current task itself is being audited. 587 */ 588 return audit_seccomp(syscall, signr, action); 589 } 590 591 /* 592 * Secure computing mode 1 allows only read/write/exit/sigreturn. 593 * To be fully secure this must be combined with rlimit 594 * to limit the stack allocations too. 595 */ 596 static const int mode1_syscalls[] = { 597 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 598 0, /* null terminated */ 599 }; 600 601 static void __secure_computing_strict(int this_syscall) 602 { 603 const int *syscall_whitelist = mode1_syscalls; 604 #ifdef CONFIG_COMPAT 605 if (in_compat_syscall()) 606 syscall_whitelist = get_compat_mode1_syscalls(); 607 #endif 608 do { 609 if (*syscall_whitelist == this_syscall) 610 return; 611 } while (*++syscall_whitelist); 612 613 #ifdef SECCOMP_DEBUG 614 dump_stack(); 615 #endif 616 seccomp_log(this_syscall, SIGKILL, SECCOMP_RET_KILL_THREAD, true); 617 do_exit(SIGKILL); 618 } 619 620 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 621 void secure_computing_strict(int this_syscall) 622 { 623 int mode = current->seccomp.mode; 624 625 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 626 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 627 return; 628 629 if (mode == SECCOMP_MODE_DISABLED) 630 return; 631 else if (mode == SECCOMP_MODE_STRICT) 632 __secure_computing_strict(this_syscall); 633 else 634 BUG(); 635 } 636 #else 637 638 #ifdef CONFIG_SECCOMP_FILTER 639 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 640 const bool recheck_after_trace) 641 { 642 u32 filter_ret, action; 643 struct seccomp_filter *match = NULL; 644 int data; 645 646 /* 647 * Make sure that any changes to mode from another thread have 648 * been seen after TIF_SECCOMP was seen. 649 */ 650 rmb(); 651 652 filter_ret = seccomp_run_filters(sd, &match); 653 data = filter_ret & SECCOMP_RET_DATA; 654 action = filter_ret & SECCOMP_RET_ACTION_FULL; 655 656 switch (action) { 657 case SECCOMP_RET_ERRNO: 658 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 659 if (data > MAX_ERRNO) 660 data = MAX_ERRNO; 661 syscall_set_return_value(current, task_pt_regs(current), 662 -data, 0); 663 goto skip; 664 665 case SECCOMP_RET_TRAP: 666 /* Show the handler the original registers. */ 667 syscall_rollback(current, task_pt_regs(current)); 668 /* Let the filter pass back 16 bits of data. */ 669 seccomp_send_sigsys(this_syscall, data); 670 goto skip; 671 672 case SECCOMP_RET_TRACE: 673 /* We've been put in this state by the ptracer already. */ 674 if (recheck_after_trace) 675 return 0; 676 677 /* ENOSYS these calls if there is no tracer attached. */ 678 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 679 syscall_set_return_value(current, 680 task_pt_regs(current), 681 -ENOSYS, 0); 682 goto skip; 683 } 684 685 /* Allow the BPF to provide the event message */ 686 ptrace_event(PTRACE_EVENT_SECCOMP, data); 687 /* 688 * The delivery of a fatal signal during event 689 * notification may silently skip tracer notification, 690 * which could leave us with a potentially unmodified 691 * syscall that the tracer would have liked to have 692 * changed. Since the process is about to die, we just 693 * force the syscall to be skipped and let the signal 694 * kill the process and correctly handle any tracer exit 695 * notifications. 696 */ 697 if (fatal_signal_pending(current)) 698 goto skip; 699 /* Check if the tracer forced the syscall to be skipped. */ 700 this_syscall = syscall_get_nr(current, task_pt_regs(current)); 701 if (this_syscall < 0) 702 goto skip; 703 704 /* 705 * Recheck the syscall, since it may have changed. This 706 * intentionally uses a NULL struct seccomp_data to force 707 * a reload of all registers. This does not goto skip since 708 * a skip would have already been reported. 709 */ 710 if (__seccomp_filter(this_syscall, NULL, true)) 711 return -1; 712 713 return 0; 714 715 case SECCOMP_RET_LOG: 716 seccomp_log(this_syscall, 0, action, true); 717 return 0; 718 719 case SECCOMP_RET_ALLOW: 720 /* 721 * Note that the "match" filter will always be NULL for 722 * this action since SECCOMP_RET_ALLOW is the starting 723 * state in seccomp_run_filters(). 724 */ 725 return 0; 726 727 case SECCOMP_RET_KILL_THREAD: 728 case SECCOMP_RET_KILL_PROCESS: 729 default: 730 seccomp_log(this_syscall, SIGSYS, action, true); 731 /* Dump core only if this is the last remaining thread. */ 732 if (action == SECCOMP_RET_KILL_PROCESS || 733 get_nr_threads(current) == 1) { 734 siginfo_t info; 735 736 /* Show the original registers in the dump. */ 737 syscall_rollback(current, task_pt_regs(current)); 738 /* Trigger a manual coredump since do_exit skips it. */ 739 seccomp_init_siginfo(&info, this_syscall, data); 740 do_coredump(&info); 741 } 742 if (action == SECCOMP_RET_KILL_PROCESS) 743 do_group_exit(SIGSYS); 744 else 745 do_exit(SIGSYS); 746 } 747 748 unreachable(); 749 750 skip: 751 seccomp_log(this_syscall, 0, action, match ? match->log : false); 752 return -1; 753 } 754 #else 755 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 756 const bool recheck_after_trace) 757 { 758 BUG(); 759 } 760 #endif 761 762 int __secure_computing(const struct seccomp_data *sd) 763 { 764 int mode = current->seccomp.mode; 765 int this_syscall; 766 767 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 768 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 769 return 0; 770 771 this_syscall = sd ? sd->nr : 772 syscall_get_nr(current, task_pt_regs(current)); 773 774 switch (mode) { 775 case SECCOMP_MODE_STRICT: 776 __secure_computing_strict(this_syscall); /* may call do_exit */ 777 return 0; 778 case SECCOMP_MODE_FILTER: 779 return __seccomp_filter(this_syscall, sd, false); 780 default: 781 BUG(); 782 } 783 } 784 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 785 786 long prctl_get_seccomp(void) 787 { 788 return current->seccomp.mode; 789 } 790 791 /** 792 * seccomp_set_mode_strict: internal function for setting strict seccomp 793 * 794 * Once current->seccomp.mode is non-zero, it may not be changed. 795 * 796 * Returns 0 on success or -EINVAL on failure. 797 */ 798 static long seccomp_set_mode_strict(void) 799 { 800 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 801 long ret = -EINVAL; 802 803 spin_lock_irq(¤t->sighand->siglock); 804 805 if (!seccomp_may_assign_mode(seccomp_mode)) 806 goto out; 807 808 #ifdef TIF_NOTSC 809 disable_TSC(); 810 #endif 811 seccomp_assign_mode(current, seccomp_mode); 812 ret = 0; 813 814 out: 815 spin_unlock_irq(¤t->sighand->siglock); 816 817 return ret; 818 } 819 820 #ifdef CONFIG_SECCOMP_FILTER 821 /** 822 * seccomp_set_mode_filter: internal function for setting seccomp filter 823 * @flags: flags to change filter behavior 824 * @filter: struct sock_fprog containing filter 825 * 826 * This function may be called repeatedly to install additional filters. 827 * Every filter successfully installed will be evaluated (in reverse order) 828 * for each system call the task makes. 829 * 830 * Once current->seccomp.mode is non-zero, it may not be changed. 831 * 832 * Returns 0 on success or -EINVAL on failure. 833 */ 834 static long seccomp_set_mode_filter(unsigned int flags, 835 const char __user *filter) 836 { 837 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 838 struct seccomp_filter *prepared = NULL; 839 long ret = -EINVAL; 840 841 /* Validate flags. */ 842 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 843 return -EINVAL; 844 845 /* Prepare the new filter before holding any locks. */ 846 prepared = seccomp_prepare_user_filter(filter); 847 if (IS_ERR(prepared)) 848 return PTR_ERR(prepared); 849 850 /* 851 * Make sure we cannot change seccomp or nnp state via TSYNC 852 * while another thread is in the middle of calling exec. 853 */ 854 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 855 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 856 goto out_free; 857 858 spin_lock_irq(¤t->sighand->siglock); 859 860 if (!seccomp_may_assign_mode(seccomp_mode)) 861 goto out; 862 863 ret = seccomp_attach_filter(flags, prepared); 864 if (ret) 865 goto out; 866 /* Do not free the successfully attached filter. */ 867 prepared = NULL; 868 869 seccomp_assign_mode(current, seccomp_mode); 870 out: 871 spin_unlock_irq(¤t->sighand->siglock); 872 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 873 mutex_unlock(¤t->signal->cred_guard_mutex); 874 out_free: 875 seccomp_filter_free(prepared); 876 return ret; 877 } 878 #else 879 static inline long seccomp_set_mode_filter(unsigned int flags, 880 const char __user *filter) 881 { 882 return -EINVAL; 883 } 884 #endif 885 886 static long seccomp_get_action_avail(const char __user *uaction) 887 { 888 u32 action; 889 890 if (copy_from_user(&action, uaction, sizeof(action))) 891 return -EFAULT; 892 893 switch (action) { 894 case SECCOMP_RET_KILL_PROCESS: 895 case SECCOMP_RET_KILL_THREAD: 896 case SECCOMP_RET_TRAP: 897 case SECCOMP_RET_ERRNO: 898 case SECCOMP_RET_TRACE: 899 case SECCOMP_RET_LOG: 900 case SECCOMP_RET_ALLOW: 901 break; 902 default: 903 return -EOPNOTSUPP; 904 } 905 906 return 0; 907 } 908 909 /* Common entry point for both prctl and syscall. */ 910 static long do_seccomp(unsigned int op, unsigned int flags, 911 const char __user *uargs) 912 { 913 switch (op) { 914 case SECCOMP_SET_MODE_STRICT: 915 if (flags != 0 || uargs != NULL) 916 return -EINVAL; 917 return seccomp_set_mode_strict(); 918 case SECCOMP_SET_MODE_FILTER: 919 return seccomp_set_mode_filter(flags, uargs); 920 case SECCOMP_GET_ACTION_AVAIL: 921 if (flags != 0) 922 return -EINVAL; 923 924 return seccomp_get_action_avail(uargs); 925 default: 926 return -EINVAL; 927 } 928 } 929 930 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 931 const char __user *, uargs) 932 { 933 return do_seccomp(op, flags, uargs); 934 } 935 936 /** 937 * prctl_set_seccomp: configures current->seccomp.mode 938 * @seccomp_mode: requested mode to use 939 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 940 * 941 * Returns 0 on success or -EINVAL on failure. 942 */ 943 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 944 { 945 unsigned int op; 946 char __user *uargs; 947 948 switch (seccomp_mode) { 949 case SECCOMP_MODE_STRICT: 950 op = SECCOMP_SET_MODE_STRICT; 951 /* 952 * Setting strict mode through prctl always ignored filter, 953 * so make sure it is always NULL here to pass the internal 954 * check in do_seccomp(). 955 */ 956 uargs = NULL; 957 break; 958 case SECCOMP_MODE_FILTER: 959 op = SECCOMP_SET_MODE_FILTER; 960 uargs = filter; 961 break; 962 default: 963 return -EINVAL; 964 } 965 966 /* prctl interface doesn't have flags, so they are always zero. */ 967 return do_seccomp(op, 0, uargs); 968 } 969 970 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) 971 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, 972 void __user *data) 973 { 974 struct seccomp_filter *filter; 975 struct sock_fprog_kern *fprog; 976 long ret; 977 unsigned long count = 0; 978 979 if (!capable(CAP_SYS_ADMIN) || 980 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 981 return -EACCES; 982 } 983 984 spin_lock_irq(&task->sighand->siglock); 985 if (task->seccomp.mode != SECCOMP_MODE_FILTER) { 986 ret = -EINVAL; 987 goto out; 988 } 989 990 filter = task->seccomp.filter; 991 while (filter) { 992 filter = filter->prev; 993 count++; 994 } 995 996 if (filter_off >= count) { 997 ret = -ENOENT; 998 goto out; 999 } 1000 count -= filter_off; 1001 1002 filter = task->seccomp.filter; 1003 while (filter && count > 1) { 1004 filter = filter->prev; 1005 count--; 1006 } 1007 1008 if (WARN_ON(count != 1 || !filter)) { 1009 /* The filter tree shouldn't shrink while we're using it. */ 1010 ret = -ENOENT; 1011 goto out; 1012 } 1013 1014 fprog = filter->prog->orig_prog; 1015 if (!fprog) { 1016 /* This must be a new non-cBPF filter, since we save 1017 * every cBPF filter's orig_prog above when 1018 * CONFIG_CHECKPOINT_RESTORE is enabled. 1019 */ 1020 ret = -EMEDIUMTYPE; 1021 goto out; 1022 } 1023 1024 ret = fprog->len; 1025 if (!data) 1026 goto out; 1027 1028 get_seccomp_filter(task); 1029 spin_unlock_irq(&task->sighand->siglock); 1030 1031 if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) 1032 ret = -EFAULT; 1033 1034 put_seccomp_filter(task); 1035 return ret; 1036 1037 out: 1038 spin_unlock_irq(&task->sighand->siglock); 1039 return ret; 1040 } 1041 #endif 1042 1043 #ifdef CONFIG_SYSCTL 1044 1045 /* Human readable action names for friendly sysctl interaction */ 1046 #define SECCOMP_RET_KILL_PROCESS_NAME "kill_process" 1047 #define SECCOMP_RET_KILL_THREAD_NAME "kill_thread" 1048 #define SECCOMP_RET_TRAP_NAME "trap" 1049 #define SECCOMP_RET_ERRNO_NAME "errno" 1050 #define SECCOMP_RET_TRACE_NAME "trace" 1051 #define SECCOMP_RET_LOG_NAME "log" 1052 #define SECCOMP_RET_ALLOW_NAME "allow" 1053 1054 static const char seccomp_actions_avail[] = 1055 SECCOMP_RET_KILL_PROCESS_NAME " " 1056 SECCOMP_RET_KILL_THREAD_NAME " " 1057 SECCOMP_RET_TRAP_NAME " " 1058 SECCOMP_RET_ERRNO_NAME " " 1059 SECCOMP_RET_TRACE_NAME " " 1060 SECCOMP_RET_LOG_NAME " " 1061 SECCOMP_RET_ALLOW_NAME; 1062 1063 struct seccomp_log_name { 1064 u32 log; 1065 const char *name; 1066 }; 1067 1068 static const struct seccomp_log_name seccomp_log_names[] = { 1069 { SECCOMP_LOG_KILL_PROCESS, SECCOMP_RET_KILL_PROCESS_NAME }, 1070 { SECCOMP_LOG_KILL_THREAD, SECCOMP_RET_KILL_THREAD_NAME }, 1071 { SECCOMP_LOG_TRAP, SECCOMP_RET_TRAP_NAME }, 1072 { SECCOMP_LOG_ERRNO, SECCOMP_RET_ERRNO_NAME }, 1073 { SECCOMP_LOG_TRACE, SECCOMP_RET_TRACE_NAME }, 1074 { SECCOMP_LOG_LOG, SECCOMP_RET_LOG_NAME }, 1075 { SECCOMP_LOG_ALLOW, SECCOMP_RET_ALLOW_NAME }, 1076 { } 1077 }; 1078 1079 static bool seccomp_names_from_actions_logged(char *names, size_t size, 1080 u32 actions_logged) 1081 { 1082 const struct seccomp_log_name *cur; 1083 bool append_space = false; 1084 1085 for (cur = seccomp_log_names; cur->name && size; cur++) { 1086 ssize_t ret; 1087 1088 if (!(actions_logged & cur->log)) 1089 continue; 1090 1091 if (append_space) { 1092 ret = strscpy(names, " ", size); 1093 if (ret < 0) 1094 return false; 1095 1096 names += ret; 1097 size -= ret; 1098 } else 1099 append_space = true; 1100 1101 ret = strscpy(names, cur->name, size); 1102 if (ret < 0) 1103 return false; 1104 1105 names += ret; 1106 size -= ret; 1107 } 1108 1109 return true; 1110 } 1111 1112 static bool seccomp_action_logged_from_name(u32 *action_logged, 1113 const char *name) 1114 { 1115 const struct seccomp_log_name *cur; 1116 1117 for (cur = seccomp_log_names; cur->name; cur++) { 1118 if (!strcmp(cur->name, name)) { 1119 *action_logged = cur->log; 1120 return true; 1121 } 1122 } 1123 1124 return false; 1125 } 1126 1127 static bool seccomp_actions_logged_from_names(u32 *actions_logged, char *names) 1128 { 1129 char *name; 1130 1131 *actions_logged = 0; 1132 while ((name = strsep(&names, " ")) && *name) { 1133 u32 action_logged = 0; 1134 1135 if (!seccomp_action_logged_from_name(&action_logged, name)) 1136 return false; 1137 1138 *actions_logged |= action_logged; 1139 } 1140 1141 return true; 1142 } 1143 1144 static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write, 1145 void __user *buffer, size_t *lenp, 1146 loff_t *ppos) 1147 { 1148 char names[sizeof(seccomp_actions_avail)]; 1149 struct ctl_table table; 1150 int ret; 1151 1152 if (write && !capable(CAP_SYS_ADMIN)) 1153 return -EPERM; 1154 1155 memset(names, 0, sizeof(names)); 1156 1157 if (!write) { 1158 if (!seccomp_names_from_actions_logged(names, sizeof(names), 1159 seccomp_actions_logged)) 1160 return -EINVAL; 1161 } 1162 1163 table = *ro_table; 1164 table.data = names; 1165 table.maxlen = sizeof(names); 1166 ret = proc_dostring(&table, write, buffer, lenp, ppos); 1167 if (ret) 1168 return ret; 1169 1170 if (write) { 1171 u32 actions_logged; 1172 1173 if (!seccomp_actions_logged_from_names(&actions_logged, 1174 table.data)) 1175 return -EINVAL; 1176 1177 if (actions_logged & SECCOMP_LOG_ALLOW) 1178 return -EINVAL; 1179 1180 seccomp_actions_logged = actions_logged; 1181 } 1182 1183 return 0; 1184 } 1185 1186 static struct ctl_path seccomp_sysctl_path[] = { 1187 { .procname = "kernel", }, 1188 { .procname = "seccomp", }, 1189 { } 1190 }; 1191 1192 static struct ctl_table seccomp_sysctl_table[] = { 1193 { 1194 .procname = "actions_avail", 1195 .data = (void *) &seccomp_actions_avail, 1196 .maxlen = sizeof(seccomp_actions_avail), 1197 .mode = 0444, 1198 .proc_handler = proc_dostring, 1199 }, 1200 { 1201 .procname = "actions_logged", 1202 .mode = 0644, 1203 .proc_handler = seccomp_actions_logged_handler, 1204 }, 1205 { } 1206 }; 1207 1208 static int __init seccomp_sysctl_init(void) 1209 { 1210 struct ctl_table_header *hdr; 1211 1212 hdr = register_sysctl_paths(seccomp_sysctl_path, seccomp_sysctl_table); 1213 if (!hdr) 1214 pr_warn("seccomp: sysctl registration failed\n"); 1215 else 1216 kmemleak_not_leak(hdr); 1217 1218 return 0; 1219 } 1220 1221 device_initcall(seccomp_sysctl_init) 1222 1223 #endif /* CONFIG_SYSCTL */ 1224