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 static void __get_seccomp_filter(struct seccomp_filter *filter) 477 { 478 /* Reference count is bounded by the number of total processes. */ 479 refcount_inc(&filter->usage); 480 } 481 482 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 483 void get_seccomp_filter(struct task_struct *tsk) 484 { 485 struct seccomp_filter *orig = tsk->seccomp.filter; 486 if (!orig) 487 return; 488 __get_seccomp_filter(orig); 489 } 490 491 static inline void seccomp_filter_free(struct seccomp_filter *filter) 492 { 493 if (filter) { 494 bpf_prog_destroy(filter->prog); 495 kfree(filter); 496 } 497 } 498 499 static void __put_seccomp_filter(struct seccomp_filter *orig) 500 { 501 /* Clean up single-reference branches iteratively. */ 502 while (orig && refcount_dec_and_test(&orig->usage)) { 503 struct seccomp_filter *freeme = orig; 504 orig = orig->prev; 505 seccomp_filter_free(freeme); 506 } 507 } 508 509 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 510 void put_seccomp_filter(struct task_struct *tsk) 511 { 512 __put_seccomp_filter(tsk->seccomp.filter); 513 } 514 515 static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason) 516 { 517 memset(info, 0, sizeof(*info)); 518 info->si_signo = SIGSYS; 519 info->si_code = SYS_SECCOMP; 520 info->si_call_addr = (void __user *)KSTK_EIP(current); 521 info->si_errno = reason; 522 info->si_arch = syscall_get_arch(); 523 info->si_syscall = syscall; 524 } 525 526 /** 527 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 528 * @syscall: syscall number to send to userland 529 * @reason: filter-supplied reason code to send to userland (via si_errno) 530 * 531 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 532 */ 533 static void seccomp_send_sigsys(int syscall, int reason) 534 { 535 struct siginfo info; 536 seccomp_init_siginfo(&info, syscall, reason); 537 force_sig_info(SIGSYS, &info, current); 538 } 539 #endif /* CONFIG_SECCOMP_FILTER */ 540 541 /* For use with seccomp_actions_logged */ 542 #define SECCOMP_LOG_KILL_PROCESS (1 << 0) 543 #define SECCOMP_LOG_KILL_THREAD (1 << 1) 544 #define SECCOMP_LOG_TRAP (1 << 2) 545 #define SECCOMP_LOG_ERRNO (1 << 3) 546 #define SECCOMP_LOG_TRACE (1 << 4) 547 #define SECCOMP_LOG_LOG (1 << 5) 548 #define SECCOMP_LOG_ALLOW (1 << 6) 549 550 static u32 seccomp_actions_logged = SECCOMP_LOG_KILL_PROCESS | 551 SECCOMP_LOG_KILL_THREAD | 552 SECCOMP_LOG_TRAP | 553 SECCOMP_LOG_ERRNO | 554 SECCOMP_LOG_TRACE | 555 SECCOMP_LOG_LOG; 556 557 static inline void seccomp_log(unsigned long syscall, long signr, u32 action, 558 bool requested) 559 { 560 bool log = false; 561 562 switch (action) { 563 case SECCOMP_RET_ALLOW: 564 break; 565 case SECCOMP_RET_TRAP: 566 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRAP; 567 break; 568 case SECCOMP_RET_ERRNO: 569 log = requested && seccomp_actions_logged & SECCOMP_LOG_ERRNO; 570 break; 571 case SECCOMP_RET_TRACE: 572 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRACE; 573 break; 574 case SECCOMP_RET_LOG: 575 log = seccomp_actions_logged & SECCOMP_LOG_LOG; 576 break; 577 case SECCOMP_RET_KILL_THREAD: 578 log = seccomp_actions_logged & SECCOMP_LOG_KILL_THREAD; 579 break; 580 case SECCOMP_RET_KILL_PROCESS: 581 default: 582 log = seccomp_actions_logged & SECCOMP_LOG_KILL_PROCESS; 583 } 584 585 /* 586 * Force an audit message to be emitted when the action is RET_KILL_*, 587 * RET_LOG, or the FILTER_FLAG_LOG bit was set and the action is 588 * allowed to be logged by the admin. 589 */ 590 if (log) 591 return __audit_seccomp(syscall, signr, action); 592 593 /* 594 * Let the audit subsystem decide if the action should be audited based 595 * on whether the current task itself is being audited. 596 */ 597 return audit_seccomp(syscall, signr, action); 598 } 599 600 /* 601 * Secure computing mode 1 allows only read/write/exit/sigreturn. 602 * To be fully secure this must be combined with rlimit 603 * to limit the stack allocations too. 604 */ 605 static const int mode1_syscalls[] = { 606 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 607 0, /* null terminated */ 608 }; 609 610 static void __secure_computing_strict(int this_syscall) 611 { 612 const int *syscall_whitelist = mode1_syscalls; 613 #ifdef CONFIG_COMPAT 614 if (in_compat_syscall()) 615 syscall_whitelist = get_compat_mode1_syscalls(); 616 #endif 617 do { 618 if (*syscall_whitelist == this_syscall) 619 return; 620 } while (*++syscall_whitelist); 621 622 #ifdef SECCOMP_DEBUG 623 dump_stack(); 624 #endif 625 seccomp_log(this_syscall, SIGKILL, SECCOMP_RET_KILL_THREAD, true); 626 do_exit(SIGKILL); 627 } 628 629 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 630 void secure_computing_strict(int this_syscall) 631 { 632 int mode = current->seccomp.mode; 633 634 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 635 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 636 return; 637 638 if (mode == SECCOMP_MODE_DISABLED) 639 return; 640 else if (mode == SECCOMP_MODE_STRICT) 641 __secure_computing_strict(this_syscall); 642 else 643 BUG(); 644 } 645 #else 646 647 #ifdef CONFIG_SECCOMP_FILTER 648 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 649 const bool recheck_after_trace) 650 { 651 u32 filter_ret, action; 652 struct seccomp_filter *match = NULL; 653 int data; 654 655 /* 656 * Make sure that any changes to mode from another thread have 657 * been seen after TIF_SECCOMP was seen. 658 */ 659 rmb(); 660 661 filter_ret = seccomp_run_filters(sd, &match); 662 data = filter_ret & SECCOMP_RET_DATA; 663 action = filter_ret & SECCOMP_RET_ACTION_FULL; 664 665 switch (action) { 666 case SECCOMP_RET_ERRNO: 667 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 668 if (data > MAX_ERRNO) 669 data = MAX_ERRNO; 670 syscall_set_return_value(current, task_pt_regs(current), 671 -data, 0); 672 goto skip; 673 674 case SECCOMP_RET_TRAP: 675 /* Show the handler the original registers. */ 676 syscall_rollback(current, task_pt_regs(current)); 677 /* Let the filter pass back 16 bits of data. */ 678 seccomp_send_sigsys(this_syscall, data); 679 goto skip; 680 681 case SECCOMP_RET_TRACE: 682 /* We've been put in this state by the ptracer already. */ 683 if (recheck_after_trace) 684 return 0; 685 686 /* ENOSYS these calls if there is no tracer attached. */ 687 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 688 syscall_set_return_value(current, 689 task_pt_regs(current), 690 -ENOSYS, 0); 691 goto skip; 692 } 693 694 /* Allow the BPF to provide the event message */ 695 ptrace_event(PTRACE_EVENT_SECCOMP, data); 696 /* 697 * The delivery of a fatal signal during event 698 * notification may silently skip tracer notification, 699 * which could leave us with a potentially unmodified 700 * syscall that the tracer would have liked to have 701 * changed. Since the process is about to die, we just 702 * force the syscall to be skipped and let the signal 703 * kill the process and correctly handle any tracer exit 704 * notifications. 705 */ 706 if (fatal_signal_pending(current)) 707 goto skip; 708 /* Check if the tracer forced the syscall to be skipped. */ 709 this_syscall = syscall_get_nr(current, task_pt_regs(current)); 710 if (this_syscall < 0) 711 goto skip; 712 713 /* 714 * Recheck the syscall, since it may have changed. This 715 * intentionally uses a NULL struct seccomp_data to force 716 * a reload of all registers. This does not goto skip since 717 * a skip would have already been reported. 718 */ 719 if (__seccomp_filter(this_syscall, NULL, true)) 720 return -1; 721 722 return 0; 723 724 case SECCOMP_RET_LOG: 725 seccomp_log(this_syscall, 0, action, true); 726 return 0; 727 728 case SECCOMP_RET_ALLOW: 729 /* 730 * Note that the "match" filter will always be NULL for 731 * this action since SECCOMP_RET_ALLOW is the starting 732 * state in seccomp_run_filters(). 733 */ 734 return 0; 735 736 case SECCOMP_RET_KILL_THREAD: 737 case SECCOMP_RET_KILL_PROCESS: 738 default: 739 seccomp_log(this_syscall, SIGSYS, action, true); 740 /* Dump core only if this is the last remaining thread. */ 741 if (action == SECCOMP_RET_KILL_PROCESS || 742 get_nr_threads(current) == 1) { 743 siginfo_t info; 744 745 /* Show the original registers in the dump. */ 746 syscall_rollback(current, task_pt_regs(current)); 747 /* Trigger a manual coredump since do_exit skips it. */ 748 seccomp_init_siginfo(&info, this_syscall, data); 749 do_coredump(&info); 750 } 751 if (action == SECCOMP_RET_KILL_PROCESS) 752 do_group_exit(SIGSYS); 753 else 754 do_exit(SIGSYS); 755 } 756 757 unreachable(); 758 759 skip: 760 seccomp_log(this_syscall, 0, action, match ? match->log : false); 761 return -1; 762 } 763 #else 764 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 765 const bool recheck_after_trace) 766 { 767 BUG(); 768 } 769 #endif 770 771 int __secure_computing(const struct seccomp_data *sd) 772 { 773 int mode = current->seccomp.mode; 774 int this_syscall; 775 776 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 777 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 778 return 0; 779 780 this_syscall = sd ? sd->nr : 781 syscall_get_nr(current, task_pt_regs(current)); 782 783 switch (mode) { 784 case SECCOMP_MODE_STRICT: 785 __secure_computing_strict(this_syscall); /* may call do_exit */ 786 return 0; 787 case SECCOMP_MODE_FILTER: 788 return __seccomp_filter(this_syscall, sd, false); 789 default: 790 BUG(); 791 } 792 } 793 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 794 795 long prctl_get_seccomp(void) 796 { 797 return current->seccomp.mode; 798 } 799 800 /** 801 * seccomp_set_mode_strict: internal function for setting strict seccomp 802 * 803 * Once current->seccomp.mode is non-zero, it may not be changed. 804 * 805 * Returns 0 on success or -EINVAL on failure. 806 */ 807 static long seccomp_set_mode_strict(void) 808 { 809 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 810 long ret = -EINVAL; 811 812 spin_lock_irq(¤t->sighand->siglock); 813 814 if (!seccomp_may_assign_mode(seccomp_mode)) 815 goto out; 816 817 #ifdef TIF_NOTSC 818 disable_TSC(); 819 #endif 820 seccomp_assign_mode(current, seccomp_mode); 821 ret = 0; 822 823 out: 824 spin_unlock_irq(¤t->sighand->siglock); 825 826 return ret; 827 } 828 829 #ifdef CONFIG_SECCOMP_FILTER 830 /** 831 * seccomp_set_mode_filter: internal function for setting seccomp filter 832 * @flags: flags to change filter behavior 833 * @filter: struct sock_fprog containing filter 834 * 835 * This function may be called repeatedly to install additional filters. 836 * Every filter successfully installed will be evaluated (in reverse order) 837 * for each system call the task makes. 838 * 839 * Once current->seccomp.mode is non-zero, it may not be changed. 840 * 841 * Returns 0 on success or -EINVAL on failure. 842 */ 843 static long seccomp_set_mode_filter(unsigned int flags, 844 const char __user *filter) 845 { 846 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 847 struct seccomp_filter *prepared = NULL; 848 long ret = -EINVAL; 849 850 /* Validate flags. */ 851 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 852 return -EINVAL; 853 854 /* Prepare the new filter before holding any locks. */ 855 prepared = seccomp_prepare_user_filter(filter); 856 if (IS_ERR(prepared)) 857 return PTR_ERR(prepared); 858 859 /* 860 * Make sure we cannot change seccomp or nnp state via TSYNC 861 * while another thread is in the middle of calling exec. 862 */ 863 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 864 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 865 goto out_free; 866 867 spin_lock_irq(¤t->sighand->siglock); 868 869 if (!seccomp_may_assign_mode(seccomp_mode)) 870 goto out; 871 872 ret = seccomp_attach_filter(flags, prepared); 873 if (ret) 874 goto out; 875 /* Do not free the successfully attached filter. */ 876 prepared = NULL; 877 878 seccomp_assign_mode(current, seccomp_mode); 879 out: 880 spin_unlock_irq(¤t->sighand->siglock); 881 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 882 mutex_unlock(¤t->signal->cred_guard_mutex); 883 out_free: 884 seccomp_filter_free(prepared); 885 return ret; 886 } 887 #else 888 static inline long seccomp_set_mode_filter(unsigned int flags, 889 const char __user *filter) 890 { 891 return -EINVAL; 892 } 893 #endif 894 895 static long seccomp_get_action_avail(const char __user *uaction) 896 { 897 u32 action; 898 899 if (copy_from_user(&action, uaction, sizeof(action))) 900 return -EFAULT; 901 902 switch (action) { 903 case SECCOMP_RET_KILL_PROCESS: 904 case SECCOMP_RET_KILL_THREAD: 905 case SECCOMP_RET_TRAP: 906 case SECCOMP_RET_ERRNO: 907 case SECCOMP_RET_TRACE: 908 case SECCOMP_RET_LOG: 909 case SECCOMP_RET_ALLOW: 910 break; 911 default: 912 return -EOPNOTSUPP; 913 } 914 915 return 0; 916 } 917 918 /* Common entry point for both prctl and syscall. */ 919 static long do_seccomp(unsigned int op, unsigned int flags, 920 const char __user *uargs) 921 { 922 switch (op) { 923 case SECCOMP_SET_MODE_STRICT: 924 if (flags != 0 || uargs != NULL) 925 return -EINVAL; 926 return seccomp_set_mode_strict(); 927 case SECCOMP_SET_MODE_FILTER: 928 return seccomp_set_mode_filter(flags, uargs); 929 case SECCOMP_GET_ACTION_AVAIL: 930 if (flags != 0) 931 return -EINVAL; 932 933 return seccomp_get_action_avail(uargs); 934 default: 935 return -EINVAL; 936 } 937 } 938 939 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 940 const char __user *, uargs) 941 { 942 return do_seccomp(op, flags, uargs); 943 } 944 945 /** 946 * prctl_set_seccomp: configures current->seccomp.mode 947 * @seccomp_mode: requested mode to use 948 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 949 * 950 * Returns 0 on success or -EINVAL on failure. 951 */ 952 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 953 { 954 unsigned int op; 955 char __user *uargs; 956 957 switch (seccomp_mode) { 958 case SECCOMP_MODE_STRICT: 959 op = SECCOMP_SET_MODE_STRICT; 960 /* 961 * Setting strict mode through prctl always ignored filter, 962 * so make sure it is always NULL here to pass the internal 963 * check in do_seccomp(). 964 */ 965 uargs = NULL; 966 break; 967 case SECCOMP_MODE_FILTER: 968 op = SECCOMP_SET_MODE_FILTER; 969 uargs = filter; 970 break; 971 default: 972 return -EINVAL; 973 } 974 975 /* prctl interface doesn't have flags, so they are always zero. */ 976 return do_seccomp(op, 0, uargs); 977 } 978 979 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) 980 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, 981 void __user *data) 982 { 983 struct seccomp_filter *filter; 984 struct sock_fprog_kern *fprog; 985 long ret; 986 unsigned long count = 0; 987 988 if (!capable(CAP_SYS_ADMIN) || 989 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 990 return -EACCES; 991 } 992 993 spin_lock_irq(&task->sighand->siglock); 994 if (task->seccomp.mode != SECCOMP_MODE_FILTER) { 995 ret = -EINVAL; 996 goto out; 997 } 998 999 filter = task->seccomp.filter; 1000 while (filter) { 1001 filter = filter->prev; 1002 count++; 1003 } 1004 1005 if (filter_off >= count) { 1006 ret = -ENOENT; 1007 goto out; 1008 } 1009 count -= filter_off; 1010 1011 filter = task->seccomp.filter; 1012 while (filter && count > 1) { 1013 filter = filter->prev; 1014 count--; 1015 } 1016 1017 if (WARN_ON(count != 1 || !filter)) { 1018 /* The filter tree shouldn't shrink while we're using it. */ 1019 ret = -ENOENT; 1020 goto out; 1021 } 1022 1023 fprog = filter->prog->orig_prog; 1024 if (!fprog) { 1025 /* This must be a new non-cBPF filter, since we save 1026 * every cBPF filter's orig_prog above when 1027 * CONFIG_CHECKPOINT_RESTORE is enabled. 1028 */ 1029 ret = -EMEDIUMTYPE; 1030 goto out; 1031 } 1032 1033 ret = fprog->len; 1034 if (!data) 1035 goto out; 1036 1037 __get_seccomp_filter(filter); 1038 spin_unlock_irq(&task->sighand->siglock); 1039 1040 if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) 1041 ret = -EFAULT; 1042 1043 __put_seccomp_filter(filter); 1044 return ret; 1045 1046 out: 1047 spin_unlock_irq(&task->sighand->siglock); 1048 return ret; 1049 } 1050 #endif 1051 1052 #ifdef CONFIG_SYSCTL 1053 1054 /* Human readable action names for friendly sysctl interaction */ 1055 #define SECCOMP_RET_KILL_PROCESS_NAME "kill_process" 1056 #define SECCOMP_RET_KILL_THREAD_NAME "kill_thread" 1057 #define SECCOMP_RET_TRAP_NAME "trap" 1058 #define SECCOMP_RET_ERRNO_NAME "errno" 1059 #define SECCOMP_RET_TRACE_NAME "trace" 1060 #define SECCOMP_RET_LOG_NAME "log" 1061 #define SECCOMP_RET_ALLOW_NAME "allow" 1062 1063 static const char seccomp_actions_avail[] = 1064 SECCOMP_RET_KILL_PROCESS_NAME " " 1065 SECCOMP_RET_KILL_THREAD_NAME " " 1066 SECCOMP_RET_TRAP_NAME " " 1067 SECCOMP_RET_ERRNO_NAME " " 1068 SECCOMP_RET_TRACE_NAME " " 1069 SECCOMP_RET_LOG_NAME " " 1070 SECCOMP_RET_ALLOW_NAME; 1071 1072 struct seccomp_log_name { 1073 u32 log; 1074 const char *name; 1075 }; 1076 1077 static const struct seccomp_log_name seccomp_log_names[] = { 1078 { SECCOMP_LOG_KILL_PROCESS, SECCOMP_RET_KILL_PROCESS_NAME }, 1079 { SECCOMP_LOG_KILL_THREAD, SECCOMP_RET_KILL_THREAD_NAME }, 1080 { SECCOMP_LOG_TRAP, SECCOMP_RET_TRAP_NAME }, 1081 { SECCOMP_LOG_ERRNO, SECCOMP_RET_ERRNO_NAME }, 1082 { SECCOMP_LOG_TRACE, SECCOMP_RET_TRACE_NAME }, 1083 { SECCOMP_LOG_LOG, SECCOMP_RET_LOG_NAME }, 1084 { SECCOMP_LOG_ALLOW, SECCOMP_RET_ALLOW_NAME }, 1085 { } 1086 }; 1087 1088 static bool seccomp_names_from_actions_logged(char *names, size_t size, 1089 u32 actions_logged) 1090 { 1091 const struct seccomp_log_name *cur; 1092 bool append_space = false; 1093 1094 for (cur = seccomp_log_names; cur->name && size; cur++) { 1095 ssize_t ret; 1096 1097 if (!(actions_logged & cur->log)) 1098 continue; 1099 1100 if (append_space) { 1101 ret = strscpy(names, " ", size); 1102 if (ret < 0) 1103 return false; 1104 1105 names += ret; 1106 size -= ret; 1107 } else 1108 append_space = true; 1109 1110 ret = strscpy(names, cur->name, size); 1111 if (ret < 0) 1112 return false; 1113 1114 names += ret; 1115 size -= ret; 1116 } 1117 1118 return true; 1119 } 1120 1121 static bool seccomp_action_logged_from_name(u32 *action_logged, 1122 const char *name) 1123 { 1124 const struct seccomp_log_name *cur; 1125 1126 for (cur = seccomp_log_names; cur->name; cur++) { 1127 if (!strcmp(cur->name, name)) { 1128 *action_logged = cur->log; 1129 return true; 1130 } 1131 } 1132 1133 return false; 1134 } 1135 1136 static bool seccomp_actions_logged_from_names(u32 *actions_logged, char *names) 1137 { 1138 char *name; 1139 1140 *actions_logged = 0; 1141 while ((name = strsep(&names, " ")) && *name) { 1142 u32 action_logged = 0; 1143 1144 if (!seccomp_action_logged_from_name(&action_logged, name)) 1145 return false; 1146 1147 *actions_logged |= action_logged; 1148 } 1149 1150 return true; 1151 } 1152 1153 static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write, 1154 void __user *buffer, size_t *lenp, 1155 loff_t *ppos) 1156 { 1157 char names[sizeof(seccomp_actions_avail)]; 1158 struct ctl_table table; 1159 int ret; 1160 1161 if (write && !capable(CAP_SYS_ADMIN)) 1162 return -EPERM; 1163 1164 memset(names, 0, sizeof(names)); 1165 1166 if (!write) { 1167 if (!seccomp_names_from_actions_logged(names, sizeof(names), 1168 seccomp_actions_logged)) 1169 return -EINVAL; 1170 } 1171 1172 table = *ro_table; 1173 table.data = names; 1174 table.maxlen = sizeof(names); 1175 ret = proc_dostring(&table, write, buffer, lenp, ppos); 1176 if (ret) 1177 return ret; 1178 1179 if (write) { 1180 u32 actions_logged; 1181 1182 if (!seccomp_actions_logged_from_names(&actions_logged, 1183 table.data)) 1184 return -EINVAL; 1185 1186 if (actions_logged & SECCOMP_LOG_ALLOW) 1187 return -EINVAL; 1188 1189 seccomp_actions_logged = actions_logged; 1190 } 1191 1192 return 0; 1193 } 1194 1195 static struct ctl_path seccomp_sysctl_path[] = { 1196 { .procname = "kernel", }, 1197 { .procname = "seccomp", }, 1198 { } 1199 }; 1200 1201 static struct ctl_table seccomp_sysctl_table[] = { 1202 { 1203 .procname = "actions_avail", 1204 .data = (void *) &seccomp_actions_avail, 1205 .maxlen = sizeof(seccomp_actions_avail), 1206 .mode = 0444, 1207 .proc_handler = proc_dostring, 1208 }, 1209 { 1210 .procname = "actions_logged", 1211 .mode = 0644, 1212 .proc_handler = seccomp_actions_logged_handler, 1213 }, 1214 { } 1215 }; 1216 1217 static int __init seccomp_sysctl_init(void) 1218 { 1219 struct ctl_table_header *hdr; 1220 1221 hdr = register_sysctl_paths(seccomp_sysctl_path, seccomp_sysctl_table); 1222 if (!hdr) 1223 pr_warn("seccomp: sysctl registration failed\n"); 1224 else 1225 kmemleak_not_leak(hdr); 1226 1227 return 0; 1228 } 1229 1230 device_initcall(seccomp_sysctl_init) 1231 1232 #endif /* CONFIG_SYSCTL */ 1233