1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * linux/kernel/seccomp.c 4 * 5 * Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com> 6 * 7 * Copyright (C) 2012 Google, Inc. 8 * Will Drewry <wad@chromium.org> 9 * 10 * This defines a simple but solid secure-computing facility. 11 * 12 * Mode 1 uses a fixed list of allowed system calls. 13 * Mode 2 allows user-defined system call filters in the form 14 * of Berkeley Packet Filters/Linux Socket Filters. 15 */ 16 17 #include <linux/refcount.h> 18 #include <linux/audit.h> 19 #include <linux/compat.h> 20 #include <linux/coredump.h> 21 #include <linux/kmemleak.h> 22 #include <linux/sched.h> 23 #include <linux/sched/task_stack.h> 24 #include <linux/seccomp.h> 25 #include <linux/slab.h> 26 #include <linux/syscalls.h> 27 #include <linux/sysctl.h> 28 29 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER 30 #include <asm/syscall.h> 31 #endif 32 33 #ifdef CONFIG_SECCOMP_FILTER 34 #include <linux/filter.h> 35 #include <linux/pid.h> 36 #include <linux/ptrace.h> 37 #include <linux/security.h> 38 #include <linux/tracehook.h> 39 #include <linux/uaccess.h> 40 41 /** 42 * struct seccomp_filter - container for seccomp BPF programs 43 * 44 * @usage: reference count to manage the object lifetime. 45 * get/put helpers should be used when accessing an instance 46 * outside of a lifetime-guarded section. In general, this 47 * is only needed for handling filters shared across tasks. 48 * @log: true if all actions except for SECCOMP_RET_ALLOW should be logged 49 * @prev: points to a previously installed, or inherited, filter 50 * @prog: the BPF program to evaluate 51 * 52 * seccomp_filter objects are organized in a tree linked via the @prev 53 * pointer. For any task, it appears to be a singly-linked list starting 54 * with current->seccomp.filter, the most recently attached or inherited filter. 55 * However, multiple filters may share a @prev node, by way of fork(), which 56 * results in a unidirectional tree existing in memory. This is similar to 57 * how namespaces work. 58 * 59 * seccomp_filter objects should never be modified after being attached 60 * to a task_struct (other than @usage). 61 */ 62 struct seccomp_filter { 63 refcount_t usage; 64 bool log; 65 struct seccomp_filter *prev; 66 struct bpf_prog *prog; 67 }; 68 69 /* Limit any path through the tree to 256KB worth of instructions. */ 70 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter)) 71 72 /* 73 * Endianness is explicitly ignored and left for BPF program authors to manage 74 * as per the specific architecture. 75 */ 76 static void populate_seccomp_data(struct seccomp_data *sd) 77 { 78 struct task_struct *task = current; 79 struct pt_regs *regs = task_pt_regs(task); 80 unsigned long args[6]; 81 82 sd->nr = syscall_get_nr(task, regs); 83 sd->arch = syscall_get_arch(); 84 syscall_get_arguments(task, regs, 0, 6, args); 85 sd->args[0] = args[0]; 86 sd->args[1] = args[1]; 87 sd->args[2] = args[2]; 88 sd->args[3] = args[3]; 89 sd->args[4] = args[4]; 90 sd->args[5] = args[5]; 91 sd->instruction_pointer = KSTK_EIP(task); 92 } 93 94 /** 95 * seccomp_check_filter - verify seccomp filter code 96 * @filter: filter to verify 97 * @flen: length of filter 98 * 99 * Takes a previously checked filter (by bpf_check_classic) and 100 * redirects all filter code that loads struct sk_buff data 101 * and related data through seccomp_bpf_load. It also 102 * enforces length and alignment checking of those loads. 103 * 104 * Returns 0 if the rule set is legal or -EINVAL if not. 105 */ 106 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) 107 { 108 int pc; 109 for (pc = 0; pc < flen; pc++) { 110 struct sock_filter *ftest = &filter[pc]; 111 u16 code = ftest->code; 112 u32 k = ftest->k; 113 114 switch (code) { 115 case BPF_LD | BPF_W | BPF_ABS: 116 ftest->code = BPF_LDX | BPF_W | BPF_ABS; 117 /* 32-bit aligned and not out of bounds. */ 118 if (k >= sizeof(struct seccomp_data) || k & 3) 119 return -EINVAL; 120 continue; 121 case BPF_LD | BPF_W | BPF_LEN: 122 ftest->code = BPF_LD | BPF_IMM; 123 ftest->k = sizeof(struct seccomp_data); 124 continue; 125 case BPF_LDX | BPF_W | BPF_LEN: 126 ftest->code = BPF_LDX | BPF_IMM; 127 ftest->k = sizeof(struct seccomp_data); 128 continue; 129 /* Explicitly include allowed calls. */ 130 case BPF_RET | BPF_K: 131 case BPF_RET | BPF_A: 132 case BPF_ALU | BPF_ADD | BPF_K: 133 case BPF_ALU | BPF_ADD | BPF_X: 134 case BPF_ALU | BPF_SUB | BPF_K: 135 case BPF_ALU | BPF_SUB | BPF_X: 136 case BPF_ALU | BPF_MUL | BPF_K: 137 case BPF_ALU | BPF_MUL | BPF_X: 138 case BPF_ALU | BPF_DIV | BPF_K: 139 case BPF_ALU | BPF_DIV | BPF_X: 140 case BPF_ALU | BPF_AND | BPF_K: 141 case BPF_ALU | BPF_AND | BPF_X: 142 case BPF_ALU | BPF_OR | BPF_K: 143 case BPF_ALU | BPF_OR | BPF_X: 144 case BPF_ALU | BPF_XOR | BPF_K: 145 case BPF_ALU | BPF_XOR | BPF_X: 146 case BPF_ALU | BPF_LSH | BPF_K: 147 case BPF_ALU | BPF_LSH | BPF_X: 148 case BPF_ALU | BPF_RSH | BPF_K: 149 case BPF_ALU | BPF_RSH | BPF_X: 150 case BPF_ALU | BPF_NEG: 151 case BPF_LD | BPF_IMM: 152 case BPF_LDX | BPF_IMM: 153 case BPF_MISC | BPF_TAX: 154 case BPF_MISC | BPF_TXA: 155 case BPF_LD | BPF_MEM: 156 case BPF_LDX | BPF_MEM: 157 case BPF_ST: 158 case BPF_STX: 159 case BPF_JMP | BPF_JA: 160 case BPF_JMP | BPF_JEQ | BPF_K: 161 case BPF_JMP | BPF_JEQ | BPF_X: 162 case BPF_JMP | BPF_JGE | BPF_K: 163 case BPF_JMP | BPF_JGE | BPF_X: 164 case BPF_JMP | BPF_JGT | BPF_K: 165 case BPF_JMP | BPF_JGT | BPF_X: 166 case BPF_JMP | BPF_JSET | BPF_K: 167 case BPF_JMP | BPF_JSET | BPF_X: 168 continue; 169 default: 170 return -EINVAL; 171 } 172 } 173 return 0; 174 } 175 176 /** 177 * seccomp_run_filters - evaluates all seccomp filters against @sd 178 * @sd: optional seccomp data to be passed to filters 179 * @match: stores struct seccomp_filter that resulted in the return value, 180 * unless filter returned SECCOMP_RET_ALLOW, in which case it will 181 * be unchanged. 182 * 183 * Returns valid seccomp BPF response codes. 184 */ 185 #define ACTION_ONLY(ret) ((s32)((ret) & (SECCOMP_RET_ACTION_FULL))) 186 static u32 seccomp_run_filters(const struct seccomp_data *sd, 187 struct seccomp_filter **match) 188 { 189 struct seccomp_data sd_local; 190 u32 ret = SECCOMP_RET_ALLOW; 191 /* Make sure cross-thread synced filter points somewhere sane. */ 192 struct seccomp_filter *f = 193 READ_ONCE(current->seccomp.filter); 194 195 /* Ensure unexpected behavior doesn't result in failing open. */ 196 if (unlikely(WARN_ON(f == NULL))) 197 return SECCOMP_RET_KILL_PROCESS; 198 199 if (!sd) { 200 populate_seccomp_data(&sd_local); 201 sd = &sd_local; 202 } 203 204 /* 205 * All filters in the list are evaluated and the lowest BPF return 206 * value always takes priority (ignoring the DATA). 207 */ 208 for (; f; f = f->prev) { 209 u32 cur_ret = BPF_PROG_RUN(f->prog, sd); 210 211 if (ACTION_ONLY(cur_ret) < ACTION_ONLY(ret)) { 212 ret = cur_ret; 213 *match = f; 214 } 215 } 216 return ret; 217 } 218 #endif /* CONFIG_SECCOMP_FILTER */ 219 220 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 221 { 222 assert_spin_locked(¤t->sighand->siglock); 223 224 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) 225 return false; 226 227 return true; 228 } 229 230 static inline void seccomp_assign_mode(struct task_struct *task, 231 unsigned long seccomp_mode) 232 { 233 assert_spin_locked(&task->sighand->siglock); 234 235 task->seccomp.mode = seccomp_mode; 236 /* 237 * Make sure TIF_SECCOMP cannot be set before the mode (and 238 * filter) is set. 239 */ 240 smp_mb__before_atomic(); 241 set_tsk_thread_flag(task, TIF_SECCOMP); 242 } 243 244 #ifdef CONFIG_SECCOMP_FILTER 245 /* Returns 1 if the parent is an ancestor of the child. */ 246 static int is_ancestor(struct seccomp_filter *parent, 247 struct seccomp_filter *child) 248 { 249 /* NULL is the root ancestor. */ 250 if (parent == NULL) 251 return 1; 252 for (; child; child = child->prev) 253 if (child == parent) 254 return 1; 255 return 0; 256 } 257 258 /** 259 * seccomp_can_sync_threads: checks if all threads can be synchronized 260 * 261 * Expects sighand and cred_guard_mutex locks to be held. 262 * 263 * Returns 0 on success, -ve on error, or the pid of a thread which was 264 * either not in the correct seccomp mode or it did not have an ancestral 265 * seccomp filter. 266 */ 267 static inline pid_t seccomp_can_sync_threads(void) 268 { 269 struct task_struct *thread, *caller; 270 271 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 272 assert_spin_locked(¤t->sighand->siglock); 273 274 /* Validate all threads being eligible for synchronization. */ 275 caller = current; 276 for_each_thread(caller, thread) { 277 pid_t failed; 278 279 /* Skip current, since it is initiating the sync. */ 280 if (thread == caller) 281 continue; 282 283 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || 284 (thread->seccomp.mode == SECCOMP_MODE_FILTER && 285 is_ancestor(thread->seccomp.filter, 286 caller->seccomp.filter))) 287 continue; 288 289 /* Return the first thread that cannot be synchronized. */ 290 failed = task_pid_vnr(thread); 291 /* If the pid cannot be resolved, then return -ESRCH */ 292 if (unlikely(WARN_ON(failed == 0))) 293 failed = -ESRCH; 294 return failed; 295 } 296 297 return 0; 298 } 299 300 /** 301 * seccomp_sync_threads: sets all threads to use current's filter 302 * 303 * Expects sighand and cred_guard_mutex locks to be held, and for 304 * seccomp_can_sync_threads() to have returned success already 305 * without dropping the locks. 306 * 307 */ 308 static inline void seccomp_sync_threads(void) 309 { 310 struct task_struct *thread, *caller; 311 312 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 313 assert_spin_locked(¤t->sighand->siglock); 314 315 /* Synchronize all threads. */ 316 caller = current; 317 for_each_thread(caller, thread) { 318 /* Skip current, since it needs no changes. */ 319 if (thread == caller) 320 continue; 321 322 /* Get a task reference for the new leaf node. */ 323 get_seccomp_filter(caller); 324 /* 325 * Drop the task reference to the shared ancestor since 326 * current's path will hold a reference. (This also 327 * allows a put before the assignment.) 328 */ 329 put_seccomp_filter(thread); 330 smp_store_release(&thread->seccomp.filter, 331 caller->seccomp.filter); 332 333 /* 334 * Don't let an unprivileged task work around 335 * the no_new_privs restriction by creating 336 * a thread that sets it up, enters seccomp, 337 * then dies. 338 */ 339 if (task_no_new_privs(caller)) 340 task_set_no_new_privs(thread); 341 342 /* 343 * Opt the other thread into seccomp if needed. 344 * As threads are considered to be trust-realm 345 * equivalent (see ptrace_may_access), it is safe to 346 * allow one thread to transition the other. 347 */ 348 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) 349 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 350 } 351 } 352 353 /** 354 * seccomp_prepare_filter: Prepares a seccomp filter for use. 355 * @fprog: BPF program to install 356 * 357 * Returns filter on success or an ERR_PTR on failure. 358 */ 359 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 360 { 361 struct seccomp_filter *sfilter; 362 int ret; 363 const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE); 364 365 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 366 return ERR_PTR(-EINVAL); 367 368 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 369 370 /* 371 * Installing a seccomp filter requires that the task has 372 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 373 * This avoids scenarios where unprivileged tasks can affect the 374 * behavior of privileged children. 375 */ 376 if (!task_no_new_privs(current) && 377 security_capable_noaudit(current_cred(), current_user_ns(), 378 CAP_SYS_ADMIN) != 0) 379 return ERR_PTR(-EACCES); 380 381 /* Allocate a new seccomp_filter */ 382 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); 383 if (!sfilter) 384 return ERR_PTR(-ENOMEM); 385 386 ret = bpf_prog_create_from_user(&sfilter->prog, fprog, 387 seccomp_check_filter, save_orig); 388 if (ret < 0) { 389 kfree(sfilter); 390 return ERR_PTR(ret); 391 } 392 393 refcount_set(&sfilter->usage, 1); 394 395 return sfilter; 396 } 397 398 /** 399 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 400 * @user_filter: pointer to the user data containing a sock_fprog. 401 * 402 * Returns 0 on success and non-zero otherwise. 403 */ 404 static struct seccomp_filter * 405 seccomp_prepare_user_filter(const char __user *user_filter) 406 { 407 struct sock_fprog fprog; 408 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 409 410 #ifdef CONFIG_COMPAT 411 if (in_compat_syscall()) { 412 struct compat_sock_fprog fprog32; 413 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 414 goto out; 415 fprog.len = fprog32.len; 416 fprog.filter = compat_ptr(fprog32.filter); 417 } else /* falls through to the if below. */ 418 #endif 419 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 420 goto out; 421 filter = seccomp_prepare_filter(&fprog); 422 out: 423 return filter; 424 } 425 426 /** 427 * seccomp_attach_filter: validate and attach filter 428 * @flags: flags to change filter behavior 429 * @filter: seccomp filter to add to the current process 430 * 431 * Caller must be holding current->sighand->siglock lock. 432 * 433 * Returns 0 on success, -ve on error. 434 */ 435 static long seccomp_attach_filter(unsigned int flags, 436 struct seccomp_filter *filter) 437 { 438 unsigned long total_insns; 439 struct seccomp_filter *walker; 440 441 assert_spin_locked(¤t->sighand->siglock); 442 443 /* Validate resulting filter length. */ 444 total_insns = filter->prog->len; 445 for (walker = current->seccomp.filter; walker; walker = walker->prev) 446 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 447 if (total_insns > MAX_INSNS_PER_PATH) 448 return -ENOMEM; 449 450 /* If thread sync has been requested, check that it is possible. */ 451 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 452 int ret; 453 454 ret = seccomp_can_sync_threads(); 455 if (ret) 456 return ret; 457 } 458 459 /* Set log flag, if present. */ 460 if (flags & SECCOMP_FILTER_FLAG_LOG) 461 filter->log = true; 462 463 /* 464 * If there is an existing filter, make it the prev and don't drop its 465 * task reference. 466 */ 467 filter->prev = current->seccomp.filter; 468 current->seccomp.filter = filter; 469 470 /* Now that the new filter is in place, synchronize to all threads. */ 471 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 472 seccomp_sync_threads(); 473 474 return 0; 475 } 476 477 static void __get_seccomp_filter(struct seccomp_filter *filter) 478 { 479 /* Reference count is bounded by the number of total processes. */ 480 refcount_inc(&filter->usage); 481 } 482 483 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 484 void get_seccomp_filter(struct task_struct *tsk) 485 { 486 struct seccomp_filter *orig = tsk->seccomp.filter; 487 if (!orig) 488 return; 489 __get_seccomp_filter(orig); 490 } 491 492 static inline void seccomp_filter_free(struct seccomp_filter *filter) 493 { 494 if (filter) { 495 bpf_prog_destroy(filter->prog); 496 kfree(filter); 497 } 498 } 499 500 static void __put_seccomp_filter(struct seccomp_filter *orig) 501 { 502 /* Clean up single-reference branches iteratively. */ 503 while (orig && refcount_dec_and_test(&orig->usage)) { 504 struct seccomp_filter *freeme = orig; 505 orig = orig->prev; 506 seccomp_filter_free(freeme); 507 } 508 } 509 510 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 511 void put_seccomp_filter(struct task_struct *tsk) 512 { 513 __put_seccomp_filter(tsk->seccomp.filter); 514 } 515 516 static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason) 517 { 518 clear_siginfo(info); 519 info->si_signo = SIGSYS; 520 info->si_code = SYS_SECCOMP; 521 info->si_call_addr = (void __user *)KSTK_EIP(current); 522 info->si_errno = reason; 523 info->si_arch = syscall_get_arch(); 524 info->si_syscall = syscall; 525 } 526 527 /** 528 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 529 * @syscall: syscall number to send to userland 530 * @reason: filter-supplied reason code to send to userland (via si_errno) 531 * 532 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 533 */ 534 static void seccomp_send_sigsys(int syscall, int reason) 535 { 536 struct siginfo info; 537 seccomp_init_siginfo(&info, syscall, reason); 538 force_sig_info(SIGSYS, &info, current); 539 } 540 #endif /* CONFIG_SECCOMP_FILTER */ 541 542 /* For use with seccomp_actions_logged */ 543 #define SECCOMP_LOG_KILL_PROCESS (1 << 0) 544 #define SECCOMP_LOG_KILL_THREAD (1 << 1) 545 #define SECCOMP_LOG_TRAP (1 << 2) 546 #define SECCOMP_LOG_ERRNO (1 << 3) 547 #define SECCOMP_LOG_TRACE (1 << 4) 548 #define SECCOMP_LOG_LOG (1 << 5) 549 #define SECCOMP_LOG_ALLOW (1 << 6) 550 551 static u32 seccomp_actions_logged = SECCOMP_LOG_KILL_PROCESS | 552 SECCOMP_LOG_KILL_THREAD | 553 SECCOMP_LOG_TRAP | 554 SECCOMP_LOG_ERRNO | 555 SECCOMP_LOG_TRACE | 556 SECCOMP_LOG_LOG; 557 558 static inline void seccomp_log(unsigned long syscall, long signr, u32 action, 559 bool requested) 560 { 561 bool log = false; 562 563 switch (action) { 564 case SECCOMP_RET_ALLOW: 565 break; 566 case SECCOMP_RET_TRAP: 567 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRAP; 568 break; 569 case SECCOMP_RET_ERRNO: 570 log = requested && seccomp_actions_logged & SECCOMP_LOG_ERRNO; 571 break; 572 case SECCOMP_RET_TRACE: 573 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRACE; 574 break; 575 case SECCOMP_RET_LOG: 576 log = seccomp_actions_logged & SECCOMP_LOG_LOG; 577 break; 578 case SECCOMP_RET_KILL_THREAD: 579 log = seccomp_actions_logged & SECCOMP_LOG_KILL_THREAD; 580 break; 581 case SECCOMP_RET_KILL_PROCESS: 582 default: 583 log = seccomp_actions_logged & SECCOMP_LOG_KILL_PROCESS; 584 } 585 586 /* 587 * Force an audit message to be emitted when the action is RET_KILL_*, 588 * RET_LOG, or the FILTER_FLAG_LOG bit was set and the action is 589 * allowed to be logged by the admin. 590 */ 591 if (log) 592 return __audit_seccomp(syscall, signr, action); 593 594 /* 595 * Let the audit subsystem decide if the action should be audited based 596 * on whether the current task itself is being audited. 597 */ 598 return audit_seccomp(syscall, signr, action); 599 } 600 601 /* 602 * Secure computing mode 1 allows only read/write/exit/sigreturn. 603 * To be fully secure this must be combined with rlimit 604 * to limit the stack allocations too. 605 */ 606 static const int mode1_syscalls[] = { 607 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 608 0, /* null terminated */ 609 }; 610 611 static void __secure_computing_strict(int this_syscall) 612 { 613 const int *syscall_whitelist = mode1_syscalls; 614 #ifdef CONFIG_COMPAT 615 if (in_compat_syscall()) 616 syscall_whitelist = get_compat_mode1_syscalls(); 617 #endif 618 do { 619 if (*syscall_whitelist == this_syscall) 620 return; 621 } while (*++syscall_whitelist); 622 623 #ifdef SECCOMP_DEBUG 624 dump_stack(); 625 #endif 626 seccomp_log(this_syscall, SIGKILL, SECCOMP_RET_KILL_THREAD, true); 627 do_exit(SIGKILL); 628 } 629 630 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 631 void secure_computing_strict(int this_syscall) 632 { 633 int mode = current->seccomp.mode; 634 635 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 636 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 637 return; 638 639 if (mode == SECCOMP_MODE_DISABLED) 640 return; 641 else if (mode == SECCOMP_MODE_STRICT) 642 __secure_computing_strict(this_syscall); 643 else 644 BUG(); 645 } 646 #else 647 648 #ifdef CONFIG_SECCOMP_FILTER 649 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 650 const bool recheck_after_trace) 651 { 652 u32 filter_ret, action; 653 struct seccomp_filter *match = NULL; 654 int data; 655 656 /* 657 * Make sure that any changes to mode from another thread have 658 * been seen after TIF_SECCOMP was seen. 659 */ 660 rmb(); 661 662 filter_ret = seccomp_run_filters(sd, &match); 663 data = filter_ret & SECCOMP_RET_DATA; 664 action = filter_ret & SECCOMP_RET_ACTION_FULL; 665 666 switch (action) { 667 case SECCOMP_RET_ERRNO: 668 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 669 if (data > MAX_ERRNO) 670 data = MAX_ERRNO; 671 syscall_set_return_value(current, task_pt_regs(current), 672 -data, 0); 673 goto skip; 674 675 case SECCOMP_RET_TRAP: 676 /* Show the handler the original registers. */ 677 syscall_rollback(current, task_pt_regs(current)); 678 /* Let the filter pass back 16 bits of data. */ 679 seccomp_send_sigsys(this_syscall, data); 680 goto skip; 681 682 case SECCOMP_RET_TRACE: 683 /* We've been put in this state by the ptracer already. */ 684 if (recheck_after_trace) 685 return 0; 686 687 /* ENOSYS these calls if there is no tracer attached. */ 688 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 689 syscall_set_return_value(current, 690 task_pt_regs(current), 691 -ENOSYS, 0); 692 goto skip; 693 } 694 695 /* Allow the BPF to provide the event message */ 696 ptrace_event(PTRACE_EVENT_SECCOMP, data); 697 /* 698 * The delivery of a fatal signal during event 699 * notification may silently skip tracer notification, 700 * which could leave us with a potentially unmodified 701 * syscall that the tracer would have liked to have 702 * changed. Since the process is about to die, we just 703 * force the syscall to be skipped and let the signal 704 * kill the process and correctly handle any tracer exit 705 * notifications. 706 */ 707 if (fatal_signal_pending(current)) 708 goto skip; 709 /* Check if the tracer forced the syscall to be skipped. */ 710 this_syscall = syscall_get_nr(current, task_pt_regs(current)); 711 if (this_syscall < 0) 712 goto skip; 713 714 /* 715 * Recheck the syscall, since it may have changed. This 716 * intentionally uses a NULL struct seccomp_data to force 717 * a reload of all registers. This does not goto skip since 718 * a skip would have already been reported. 719 */ 720 if (__seccomp_filter(this_syscall, NULL, true)) 721 return -1; 722 723 return 0; 724 725 case SECCOMP_RET_LOG: 726 seccomp_log(this_syscall, 0, action, true); 727 return 0; 728 729 case SECCOMP_RET_ALLOW: 730 /* 731 * Note that the "match" filter will always be NULL for 732 * this action since SECCOMP_RET_ALLOW is the starting 733 * state in seccomp_run_filters(). 734 */ 735 return 0; 736 737 case SECCOMP_RET_KILL_THREAD: 738 case SECCOMP_RET_KILL_PROCESS: 739 default: 740 seccomp_log(this_syscall, SIGSYS, action, true); 741 /* Dump core only if this is the last remaining thread. */ 742 if (action == SECCOMP_RET_KILL_PROCESS || 743 get_nr_threads(current) == 1) { 744 siginfo_t info; 745 746 /* Show the original registers in the dump. */ 747 syscall_rollback(current, task_pt_regs(current)); 748 /* Trigger a manual coredump since do_exit skips it. */ 749 seccomp_init_siginfo(&info, this_syscall, data); 750 do_coredump(&info); 751 } 752 if (action == SECCOMP_RET_KILL_PROCESS) 753 do_group_exit(SIGSYS); 754 else 755 do_exit(SIGSYS); 756 } 757 758 unreachable(); 759 760 skip: 761 seccomp_log(this_syscall, 0, action, match ? match->log : false); 762 return -1; 763 } 764 #else 765 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 766 const bool recheck_after_trace) 767 { 768 BUG(); 769 } 770 #endif 771 772 int __secure_computing(const struct seccomp_data *sd) 773 { 774 int mode = current->seccomp.mode; 775 int this_syscall; 776 777 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 778 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 779 return 0; 780 781 this_syscall = sd ? sd->nr : 782 syscall_get_nr(current, task_pt_regs(current)); 783 784 switch (mode) { 785 case SECCOMP_MODE_STRICT: 786 __secure_computing_strict(this_syscall); /* may call do_exit */ 787 return 0; 788 case SECCOMP_MODE_FILTER: 789 return __seccomp_filter(this_syscall, sd, false); 790 default: 791 BUG(); 792 } 793 } 794 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 795 796 long prctl_get_seccomp(void) 797 { 798 return current->seccomp.mode; 799 } 800 801 /** 802 * seccomp_set_mode_strict: internal function for setting strict seccomp 803 * 804 * Once current->seccomp.mode is non-zero, it may not be changed. 805 * 806 * Returns 0 on success or -EINVAL on failure. 807 */ 808 static long seccomp_set_mode_strict(void) 809 { 810 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 811 long ret = -EINVAL; 812 813 spin_lock_irq(¤t->sighand->siglock); 814 815 if (!seccomp_may_assign_mode(seccomp_mode)) 816 goto out; 817 818 #ifdef TIF_NOTSC 819 disable_TSC(); 820 #endif 821 seccomp_assign_mode(current, seccomp_mode); 822 ret = 0; 823 824 out: 825 spin_unlock_irq(¤t->sighand->siglock); 826 827 return ret; 828 } 829 830 #ifdef CONFIG_SECCOMP_FILTER 831 /** 832 * seccomp_set_mode_filter: internal function for setting seccomp filter 833 * @flags: flags to change filter behavior 834 * @filter: struct sock_fprog containing filter 835 * 836 * This function may be called repeatedly to install additional filters. 837 * Every filter successfully installed will be evaluated (in reverse order) 838 * for each system call the task makes. 839 * 840 * Once current->seccomp.mode is non-zero, it may not be changed. 841 * 842 * Returns 0 on success or -EINVAL on failure. 843 */ 844 static long seccomp_set_mode_filter(unsigned int flags, 845 const char __user *filter) 846 { 847 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 848 struct seccomp_filter *prepared = NULL; 849 long ret = -EINVAL; 850 851 /* Validate flags. */ 852 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 853 return -EINVAL; 854 855 /* Prepare the new filter before holding any locks. */ 856 prepared = seccomp_prepare_user_filter(filter); 857 if (IS_ERR(prepared)) 858 return PTR_ERR(prepared); 859 860 /* 861 * Make sure we cannot change seccomp or nnp state via TSYNC 862 * while another thread is in the middle of calling exec. 863 */ 864 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 865 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 866 goto out_free; 867 868 spin_lock_irq(¤t->sighand->siglock); 869 870 if (!seccomp_may_assign_mode(seccomp_mode)) 871 goto out; 872 873 ret = seccomp_attach_filter(flags, prepared); 874 if (ret) 875 goto out; 876 /* Do not free the successfully attached filter. */ 877 prepared = NULL; 878 879 seccomp_assign_mode(current, seccomp_mode); 880 out: 881 spin_unlock_irq(¤t->sighand->siglock); 882 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 883 mutex_unlock(¤t->signal->cred_guard_mutex); 884 out_free: 885 seccomp_filter_free(prepared); 886 return ret; 887 } 888 #else 889 static inline long seccomp_set_mode_filter(unsigned int flags, 890 const char __user *filter) 891 { 892 return -EINVAL; 893 } 894 #endif 895 896 static long seccomp_get_action_avail(const char __user *uaction) 897 { 898 u32 action; 899 900 if (copy_from_user(&action, uaction, sizeof(action))) 901 return -EFAULT; 902 903 switch (action) { 904 case SECCOMP_RET_KILL_PROCESS: 905 case SECCOMP_RET_KILL_THREAD: 906 case SECCOMP_RET_TRAP: 907 case SECCOMP_RET_ERRNO: 908 case SECCOMP_RET_TRACE: 909 case SECCOMP_RET_LOG: 910 case SECCOMP_RET_ALLOW: 911 break; 912 default: 913 return -EOPNOTSUPP; 914 } 915 916 return 0; 917 } 918 919 /* Common entry point for both prctl and syscall. */ 920 static long do_seccomp(unsigned int op, unsigned int flags, 921 const char __user *uargs) 922 { 923 switch (op) { 924 case SECCOMP_SET_MODE_STRICT: 925 if (flags != 0 || uargs != NULL) 926 return -EINVAL; 927 return seccomp_set_mode_strict(); 928 case SECCOMP_SET_MODE_FILTER: 929 return seccomp_set_mode_filter(flags, uargs); 930 case SECCOMP_GET_ACTION_AVAIL: 931 if (flags != 0) 932 return -EINVAL; 933 934 return seccomp_get_action_avail(uargs); 935 default: 936 return -EINVAL; 937 } 938 } 939 940 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 941 const char __user *, uargs) 942 { 943 return do_seccomp(op, flags, uargs); 944 } 945 946 /** 947 * prctl_set_seccomp: configures current->seccomp.mode 948 * @seccomp_mode: requested mode to use 949 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 950 * 951 * Returns 0 on success or -EINVAL on failure. 952 */ 953 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 954 { 955 unsigned int op; 956 char __user *uargs; 957 958 switch (seccomp_mode) { 959 case SECCOMP_MODE_STRICT: 960 op = SECCOMP_SET_MODE_STRICT; 961 /* 962 * Setting strict mode through prctl always ignored filter, 963 * so make sure it is always NULL here to pass the internal 964 * check in do_seccomp(). 965 */ 966 uargs = NULL; 967 break; 968 case SECCOMP_MODE_FILTER: 969 op = SECCOMP_SET_MODE_FILTER; 970 uargs = filter; 971 break; 972 default: 973 return -EINVAL; 974 } 975 976 /* prctl interface doesn't have flags, so they are always zero. */ 977 return do_seccomp(op, 0, uargs); 978 } 979 980 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) 981 static struct seccomp_filter *get_nth_filter(struct task_struct *task, 982 unsigned long filter_off) 983 { 984 struct seccomp_filter *orig, *filter; 985 unsigned long count; 986 987 /* 988 * Note: this is only correct because the caller should be the (ptrace) 989 * tracer of the task, otherwise lock_task_sighand is needed. 990 */ 991 spin_lock_irq(&task->sighand->siglock); 992 993 if (task->seccomp.mode != SECCOMP_MODE_FILTER) { 994 spin_unlock_irq(&task->sighand->siglock); 995 return ERR_PTR(-EINVAL); 996 } 997 998 orig = task->seccomp.filter; 999 __get_seccomp_filter(orig); 1000 spin_unlock_irq(&task->sighand->siglock); 1001 1002 count = 0; 1003 for (filter = orig; filter; filter = filter->prev) 1004 count++; 1005 1006 if (filter_off >= count) { 1007 filter = ERR_PTR(-ENOENT); 1008 goto out; 1009 } 1010 1011 count -= filter_off; 1012 for (filter = orig; filter && count > 1; filter = filter->prev) 1013 count--; 1014 1015 if (WARN_ON(count != 1 || !filter)) { 1016 filter = ERR_PTR(-ENOENT); 1017 goto out; 1018 } 1019 1020 __get_seccomp_filter(filter); 1021 1022 out: 1023 __put_seccomp_filter(orig); 1024 return filter; 1025 } 1026 1027 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, 1028 void __user *data) 1029 { 1030 struct seccomp_filter *filter; 1031 struct sock_fprog_kern *fprog; 1032 long ret; 1033 1034 if (!capable(CAP_SYS_ADMIN) || 1035 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 1036 return -EACCES; 1037 } 1038 1039 filter = get_nth_filter(task, filter_off); 1040 if (IS_ERR(filter)) 1041 return PTR_ERR(filter); 1042 1043 fprog = filter->prog->orig_prog; 1044 if (!fprog) { 1045 /* This must be a new non-cBPF filter, since we save 1046 * every cBPF filter's orig_prog above when 1047 * CONFIG_CHECKPOINT_RESTORE is enabled. 1048 */ 1049 ret = -EMEDIUMTYPE; 1050 goto out; 1051 } 1052 1053 ret = fprog->len; 1054 if (!data) 1055 goto out; 1056 1057 if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) 1058 ret = -EFAULT; 1059 1060 out: 1061 __put_seccomp_filter(filter); 1062 return ret; 1063 } 1064 1065 long seccomp_get_metadata(struct task_struct *task, 1066 unsigned long size, void __user *data) 1067 { 1068 long ret; 1069 struct seccomp_filter *filter; 1070 struct seccomp_metadata kmd = {}; 1071 1072 if (!capable(CAP_SYS_ADMIN) || 1073 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 1074 return -EACCES; 1075 } 1076 1077 size = min_t(unsigned long, size, sizeof(kmd)); 1078 1079 if (copy_from_user(&kmd, data, size)) 1080 return -EFAULT; 1081 1082 filter = get_nth_filter(task, kmd.filter_off); 1083 if (IS_ERR(filter)) 1084 return PTR_ERR(filter); 1085 1086 memset(&kmd, 0, sizeof(kmd)); 1087 if (filter->log) 1088 kmd.flags |= SECCOMP_FILTER_FLAG_LOG; 1089 1090 ret = size; 1091 if (copy_to_user(data, &kmd, size)) 1092 ret = -EFAULT; 1093 1094 __put_seccomp_filter(filter); 1095 return ret; 1096 } 1097 #endif 1098 1099 #ifdef CONFIG_SYSCTL 1100 1101 /* Human readable action names for friendly sysctl interaction */ 1102 #define SECCOMP_RET_KILL_PROCESS_NAME "kill_process" 1103 #define SECCOMP_RET_KILL_THREAD_NAME "kill_thread" 1104 #define SECCOMP_RET_TRAP_NAME "trap" 1105 #define SECCOMP_RET_ERRNO_NAME "errno" 1106 #define SECCOMP_RET_TRACE_NAME "trace" 1107 #define SECCOMP_RET_LOG_NAME "log" 1108 #define SECCOMP_RET_ALLOW_NAME "allow" 1109 1110 static const char seccomp_actions_avail[] = 1111 SECCOMP_RET_KILL_PROCESS_NAME " " 1112 SECCOMP_RET_KILL_THREAD_NAME " " 1113 SECCOMP_RET_TRAP_NAME " " 1114 SECCOMP_RET_ERRNO_NAME " " 1115 SECCOMP_RET_TRACE_NAME " " 1116 SECCOMP_RET_LOG_NAME " " 1117 SECCOMP_RET_ALLOW_NAME; 1118 1119 struct seccomp_log_name { 1120 u32 log; 1121 const char *name; 1122 }; 1123 1124 static const struct seccomp_log_name seccomp_log_names[] = { 1125 { SECCOMP_LOG_KILL_PROCESS, SECCOMP_RET_KILL_PROCESS_NAME }, 1126 { SECCOMP_LOG_KILL_THREAD, SECCOMP_RET_KILL_THREAD_NAME }, 1127 { SECCOMP_LOG_TRAP, SECCOMP_RET_TRAP_NAME }, 1128 { SECCOMP_LOG_ERRNO, SECCOMP_RET_ERRNO_NAME }, 1129 { SECCOMP_LOG_TRACE, SECCOMP_RET_TRACE_NAME }, 1130 { SECCOMP_LOG_LOG, SECCOMP_RET_LOG_NAME }, 1131 { SECCOMP_LOG_ALLOW, SECCOMP_RET_ALLOW_NAME }, 1132 { } 1133 }; 1134 1135 static bool seccomp_names_from_actions_logged(char *names, size_t size, 1136 u32 actions_logged) 1137 { 1138 const struct seccomp_log_name *cur; 1139 bool append_space = false; 1140 1141 for (cur = seccomp_log_names; cur->name && size; cur++) { 1142 ssize_t ret; 1143 1144 if (!(actions_logged & cur->log)) 1145 continue; 1146 1147 if (append_space) { 1148 ret = strscpy(names, " ", size); 1149 if (ret < 0) 1150 return false; 1151 1152 names += ret; 1153 size -= ret; 1154 } else 1155 append_space = true; 1156 1157 ret = strscpy(names, cur->name, size); 1158 if (ret < 0) 1159 return false; 1160 1161 names += ret; 1162 size -= ret; 1163 } 1164 1165 return true; 1166 } 1167 1168 static bool seccomp_action_logged_from_name(u32 *action_logged, 1169 const char *name) 1170 { 1171 const struct seccomp_log_name *cur; 1172 1173 for (cur = seccomp_log_names; cur->name; cur++) { 1174 if (!strcmp(cur->name, name)) { 1175 *action_logged = cur->log; 1176 return true; 1177 } 1178 } 1179 1180 return false; 1181 } 1182 1183 static bool seccomp_actions_logged_from_names(u32 *actions_logged, char *names) 1184 { 1185 char *name; 1186 1187 *actions_logged = 0; 1188 while ((name = strsep(&names, " ")) && *name) { 1189 u32 action_logged = 0; 1190 1191 if (!seccomp_action_logged_from_name(&action_logged, name)) 1192 return false; 1193 1194 *actions_logged |= action_logged; 1195 } 1196 1197 return true; 1198 } 1199 1200 static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write, 1201 void __user *buffer, size_t *lenp, 1202 loff_t *ppos) 1203 { 1204 char names[sizeof(seccomp_actions_avail)]; 1205 struct ctl_table table; 1206 int ret; 1207 1208 if (write && !capable(CAP_SYS_ADMIN)) 1209 return -EPERM; 1210 1211 memset(names, 0, sizeof(names)); 1212 1213 if (!write) { 1214 if (!seccomp_names_from_actions_logged(names, sizeof(names), 1215 seccomp_actions_logged)) 1216 return -EINVAL; 1217 } 1218 1219 table = *ro_table; 1220 table.data = names; 1221 table.maxlen = sizeof(names); 1222 ret = proc_dostring(&table, write, buffer, lenp, ppos); 1223 if (ret) 1224 return ret; 1225 1226 if (write) { 1227 u32 actions_logged; 1228 1229 if (!seccomp_actions_logged_from_names(&actions_logged, 1230 table.data)) 1231 return -EINVAL; 1232 1233 if (actions_logged & SECCOMP_LOG_ALLOW) 1234 return -EINVAL; 1235 1236 seccomp_actions_logged = actions_logged; 1237 } 1238 1239 return 0; 1240 } 1241 1242 static struct ctl_path seccomp_sysctl_path[] = { 1243 { .procname = "kernel", }, 1244 { .procname = "seccomp", }, 1245 { } 1246 }; 1247 1248 static struct ctl_table seccomp_sysctl_table[] = { 1249 { 1250 .procname = "actions_avail", 1251 .data = (void *) &seccomp_actions_avail, 1252 .maxlen = sizeof(seccomp_actions_avail), 1253 .mode = 0444, 1254 .proc_handler = proc_dostring, 1255 }, 1256 { 1257 .procname = "actions_logged", 1258 .mode = 0644, 1259 .proc_handler = seccomp_actions_logged_handler, 1260 }, 1261 { } 1262 }; 1263 1264 static int __init seccomp_sysctl_init(void) 1265 { 1266 struct ctl_table_header *hdr; 1267 1268 hdr = register_sysctl_paths(seccomp_sysctl_path, seccomp_sysctl_table); 1269 if (!hdr) 1270 pr_warn("seccomp: sysctl registration failed\n"); 1271 else 1272 kmemleak_not_leak(hdr); 1273 1274 return 0; 1275 } 1276 1277 device_initcall(seccomp_sysctl_init) 1278 1279 #endif /* CONFIG_SYSCTL */ 1280