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/nospec.h> 23 #include <linux/prctl.h> 24 #include <linux/sched.h> 25 #include <linux/sched/task_stack.h> 26 #include <linux/seccomp.h> 27 #include <linux/slab.h> 28 #include <linux/syscalls.h> 29 #include <linux/sysctl.h> 30 31 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER 32 #include <asm/syscall.h> 33 #endif 34 35 #ifdef CONFIG_SECCOMP_FILTER 36 #include <linux/filter.h> 37 #include <linux/pid.h> 38 #include <linux/ptrace.h> 39 #include <linux/security.h> 40 #include <linux/tracehook.h> 41 #include <linux/uaccess.h> 42 43 /** 44 * struct seccomp_filter - container for seccomp BPF programs 45 * 46 * @usage: reference count to manage the object lifetime. 47 * get/put helpers should be used when accessing an instance 48 * outside of a lifetime-guarded section. In general, this 49 * is only needed for handling filters shared across tasks. 50 * @log: true if all actions except for SECCOMP_RET_ALLOW should be logged 51 * @prev: points to a previously installed, or inherited, filter 52 * @prog: the BPF program to evaluate 53 * 54 * seccomp_filter objects are organized in a tree linked via the @prev 55 * pointer. For any task, it appears to be a singly-linked list starting 56 * with current->seccomp.filter, the most recently attached or inherited filter. 57 * However, multiple filters may share a @prev node, by way of fork(), which 58 * results in a unidirectional tree existing in memory. This is similar to 59 * how namespaces work. 60 * 61 * seccomp_filter objects should never be modified after being attached 62 * to a task_struct (other than @usage). 63 */ 64 struct seccomp_filter { 65 refcount_t usage; 66 bool log; 67 struct seccomp_filter *prev; 68 struct bpf_prog *prog; 69 }; 70 71 /* Limit any path through the tree to 256KB worth of instructions. */ 72 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter)) 73 74 /* 75 * Endianness is explicitly ignored and left for BPF program authors to manage 76 * as per the specific architecture. 77 */ 78 static void populate_seccomp_data(struct seccomp_data *sd) 79 { 80 struct task_struct *task = current; 81 struct pt_regs *regs = task_pt_regs(task); 82 unsigned long args[6]; 83 84 sd->nr = syscall_get_nr(task, regs); 85 sd->arch = syscall_get_arch(); 86 syscall_get_arguments(task, regs, 0, 6, args); 87 sd->args[0] = args[0]; 88 sd->args[1] = args[1]; 89 sd->args[2] = args[2]; 90 sd->args[3] = args[3]; 91 sd->args[4] = args[4]; 92 sd->args[5] = args[5]; 93 sd->instruction_pointer = KSTK_EIP(task); 94 } 95 96 /** 97 * seccomp_check_filter - verify seccomp filter code 98 * @filter: filter to verify 99 * @flen: length of filter 100 * 101 * Takes a previously checked filter (by bpf_check_classic) and 102 * redirects all filter code that loads struct sk_buff data 103 * and related data through seccomp_bpf_load. It also 104 * enforces length and alignment checking of those loads. 105 * 106 * Returns 0 if the rule set is legal or -EINVAL if not. 107 */ 108 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) 109 { 110 int pc; 111 for (pc = 0; pc < flen; pc++) { 112 struct sock_filter *ftest = &filter[pc]; 113 u16 code = ftest->code; 114 u32 k = ftest->k; 115 116 switch (code) { 117 case BPF_LD | BPF_W | BPF_ABS: 118 ftest->code = BPF_LDX | BPF_W | BPF_ABS; 119 /* 32-bit aligned and not out of bounds. */ 120 if (k >= sizeof(struct seccomp_data) || k & 3) 121 return -EINVAL; 122 continue; 123 case BPF_LD | BPF_W | BPF_LEN: 124 ftest->code = BPF_LD | BPF_IMM; 125 ftest->k = sizeof(struct seccomp_data); 126 continue; 127 case BPF_LDX | BPF_W | BPF_LEN: 128 ftest->code = BPF_LDX | BPF_IMM; 129 ftest->k = sizeof(struct seccomp_data); 130 continue; 131 /* Explicitly include allowed calls. */ 132 case BPF_RET | BPF_K: 133 case BPF_RET | BPF_A: 134 case BPF_ALU | BPF_ADD | BPF_K: 135 case BPF_ALU | BPF_ADD | BPF_X: 136 case BPF_ALU | BPF_SUB | BPF_K: 137 case BPF_ALU | BPF_SUB | BPF_X: 138 case BPF_ALU | BPF_MUL | BPF_K: 139 case BPF_ALU | BPF_MUL | BPF_X: 140 case BPF_ALU | BPF_DIV | BPF_K: 141 case BPF_ALU | BPF_DIV | BPF_X: 142 case BPF_ALU | BPF_AND | BPF_K: 143 case BPF_ALU | BPF_AND | BPF_X: 144 case BPF_ALU | BPF_OR | BPF_K: 145 case BPF_ALU | BPF_OR | BPF_X: 146 case BPF_ALU | BPF_XOR | BPF_K: 147 case BPF_ALU | BPF_XOR | BPF_X: 148 case BPF_ALU | BPF_LSH | BPF_K: 149 case BPF_ALU | BPF_LSH | BPF_X: 150 case BPF_ALU | BPF_RSH | BPF_K: 151 case BPF_ALU | BPF_RSH | BPF_X: 152 case BPF_ALU | BPF_NEG: 153 case BPF_LD | BPF_IMM: 154 case BPF_LDX | BPF_IMM: 155 case BPF_MISC | BPF_TAX: 156 case BPF_MISC | BPF_TXA: 157 case BPF_LD | BPF_MEM: 158 case BPF_LDX | BPF_MEM: 159 case BPF_ST: 160 case BPF_STX: 161 case BPF_JMP | BPF_JA: 162 case BPF_JMP | BPF_JEQ | BPF_K: 163 case BPF_JMP | BPF_JEQ | BPF_X: 164 case BPF_JMP | BPF_JGE | BPF_K: 165 case BPF_JMP | BPF_JGE | BPF_X: 166 case BPF_JMP | BPF_JGT | BPF_K: 167 case BPF_JMP | BPF_JGT | BPF_X: 168 case BPF_JMP | BPF_JSET | BPF_K: 169 case BPF_JMP | BPF_JSET | BPF_X: 170 continue; 171 default: 172 return -EINVAL; 173 } 174 } 175 return 0; 176 } 177 178 /** 179 * seccomp_run_filters - evaluates all seccomp filters against @sd 180 * @sd: optional seccomp data to be passed to filters 181 * @match: stores struct seccomp_filter that resulted in the return value, 182 * unless filter returned SECCOMP_RET_ALLOW, in which case it will 183 * be unchanged. 184 * 185 * Returns valid seccomp BPF response codes. 186 */ 187 #define ACTION_ONLY(ret) ((s32)((ret) & (SECCOMP_RET_ACTION_FULL))) 188 static u32 seccomp_run_filters(const struct seccomp_data *sd, 189 struct seccomp_filter **match) 190 { 191 struct seccomp_data sd_local; 192 u32 ret = SECCOMP_RET_ALLOW; 193 /* Make sure cross-thread synced filter points somewhere sane. */ 194 struct seccomp_filter *f = 195 READ_ONCE(current->seccomp.filter); 196 197 /* Ensure unexpected behavior doesn't result in failing open. */ 198 if (unlikely(WARN_ON(f == NULL))) 199 return SECCOMP_RET_KILL_PROCESS; 200 201 if (!sd) { 202 populate_seccomp_data(&sd_local); 203 sd = &sd_local; 204 } 205 206 /* 207 * All filters in the list are evaluated and the lowest BPF return 208 * value always takes priority (ignoring the DATA). 209 */ 210 for (; f; f = f->prev) { 211 u32 cur_ret = BPF_PROG_RUN(f->prog, sd); 212 213 if (ACTION_ONLY(cur_ret) < ACTION_ONLY(ret)) { 214 ret = cur_ret; 215 *match = f; 216 } 217 } 218 return ret; 219 } 220 #endif /* CONFIG_SECCOMP_FILTER */ 221 222 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 223 { 224 assert_spin_locked(¤t->sighand->siglock); 225 226 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) 227 return false; 228 229 return true; 230 } 231 232 void __weak arch_seccomp_spec_mitigate(struct task_struct *task) { } 233 234 static inline void seccomp_assign_mode(struct task_struct *task, 235 unsigned long seccomp_mode, 236 unsigned long flags) 237 { 238 assert_spin_locked(&task->sighand->siglock); 239 240 task->seccomp.mode = seccomp_mode; 241 /* 242 * Make sure TIF_SECCOMP cannot be set before the mode (and 243 * filter) is set. 244 */ 245 smp_mb__before_atomic(); 246 /* Assume default seccomp processes want spec flaw mitigation. */ 247 if ((flags & SECCOMP_FILTER_FLAG_SPEC_ALLOW) == 0) 248 arch_seccomp_spec_mitigate(task); 249 set_tsk_thread_flag(task, TIF_SECCOMP); 250 } 251 252 #ifdef CONFIG_SECCOMP_FILTER 253 /* Returns 1 if the parent is an ancestor of the child. */ 254 static int is_ancestor(struct seccomp_filter *parent, 255 struct seccomp_filter *child) 256 { 257 /* NULL is the root ancestor. */ 258 if (parent == NULL) 259 return 1; 260 for (; child; child = child->prev) 261 if (child == parent) 262 return 1; 263 return 0; 264 } 265 266 /** 267 * seccomp_can_sync_threads: checks if all threads can be synchronized 268 * 269 * Expects sighand and cred_guard_mutex locks to be held. 270 * 271 * Returns 0 on success, -ve on error, or the pid of a thread which was 272 * either not in the correct seccomp mode or it did not have an ancestral 273 * seccomp filter. 274 */ 275 static inline pid_t seccomp_can_sync_threads(void) 276 { 277 struct task_struct *thread, *caller; 278 279 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 280 assert_spin_locked(¤t->sighand->siglock); 281 282 /* Validate all threads being eligible for synchronization. */ 283 caller = current; 284 for_each_thread(caller, thread) { 285 pid_t failed; 286 287 /* Skip current, since it is initiating the sync. */ 288 if (thread == caller) 289 continue; 290 291 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || 292 (thread->seccomp.mode == SECCOMP_MODE_FILTER && 293 is_ancestor(thread->seccomp.filter, 294 caller->seccomp.filter))) 295 continue; 296 297 /* Return the first thread that cannot be synchronized. */ 298 failed = task_pid_vnr(thread); 299 /* If the pid cannot be resolved, then return -ESRCH */ 300 if (unlikely(WARN_ON(failed == 0))) 301 failed = -ESRCH; 302 return failed; 303 } 304 305 return 0; 306 } 307 308 /** 309 * seccomp_sync_threads: sets all threads to use current's filter 310 * 311 * Expects sighand and cred_guard_mutex locks to be held, and for 312 * seccomp_can_sync_threads() to have returned success already 313 * without dropping the locks. 314 * 315 */ 316 static inline void seccomp_sync_threads(unsigned long flags) 317 { 318 struct task_struct *thread, *caller; 319 320 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 321 assert_spin_locked(¤t->sighand->siglock); 322 323 /* Synchronize all threads. */ 324 caller = current; 325 for_each_thread(caller, thread) { 326 /* Skip current, since it needs no changes. */ 327 if (thread == caller) 328 continue; 329 330 /* Get a task reference for the new leaf node. */ 331 get_seccomp_filter(caller); 332 /* 333 * Drop the task reference to the shared ancestor since 334 * current's path will hold a reference. (This also 335 * allows a put before the assignment.) 336 */ 337 put_seccomp_filter(thread); 338 smp_store_release(&thread->seccomp.filter, 339 caller->seccomp.filter); 340 341 /* 342 * Don't let an unprivileged task work around 343 * the no_new_privs restriction by creating 344 * a thread that sets it up, enters seccomp, 345 * then dies. 346 */ 347 if (task_no_new_privs(caller)) 348 task_set_no_new_privs(thread); 349 350 /* 351 * Opt the other thread into seccomp if needed. 352 * As threads are considered to be trust-realm 353 * equivalent (see ptrace_may_access), it is safe to 354 * allow one thread to transition the other. 355 */ 356 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) 357 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER, 358 flags); 359 } 360 } 361 362 /** 363 * seccomp_prepare_filter: Prepares a seccomp filter for use. 364 * @fprog: BPF program to install 365 * 366 * Returns filter on success or an ERR_PTR on failure. 367 */ 368 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 369 { 370 struct seccomp_filter *sfilter; 371 int ret; 372 const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE); 373 374 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 375 return ERR_PTR(-EINVAL); 376 377 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 378 379 /* 380 * Installing a seccomp filter requires that the task has 381 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 382 * This avoids scenarios where unprivileged tasks can affect the 383 * behavior of privileged children. 384 */ 385 if (!task_no_new_privs(current) && 386 security_capable_noaudit(current_cred(), current_user_ns(), 387 CAP_SYS_ADMIN) != 0) 388 return ERR_PTR(-EACCES); 389 390 /* Allocate a new seccomp_filter */ 391 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); 392 if (!sfilter) 393 return ERR_PTR(-ENOMEM); 394 395 ret = bpf_prog_create_from_user(&sfilter->prog, fprog, 396 seccomp_check_filter, save_orig); 397 if (ret < 0) { 398 kfree(sfilter); 399 return ERR_PTR(ret); 400 } 401 402 refcount_set(&sfilter->usage, 1); 403 404 return sfilter; 405 } 406 407 /** 408 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 409 * @user_filter: pointer to the user data containing a sock_fprog. 410 * 411 * Returns 0 on success and non-zero otherwise. 412 */ 413 static struct seccomp_filter * 414 seccomp_prepare_user_filter(const char __user *user_filter) 415 { 416 struct sock_fprog fprog; 417 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 418 419 #ifdef CONFIG_COMPAT 420 if (in_compat_syscall()) { 421 struct compat_sock_fprog fprog32; 422 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 423 goto out; 424 fprog.len = fprog32.len; 425 fprog.filter = compat_ptr(fprog32.filter); 426 } else /* falls through to the if below. */ 427 #endif 428 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 429 goto out; 430 filter = seccomp_prepare_filter(&fprog); 431 out: 432 return filter; 433 } 434 435 /** 436 * seccomp_attach_filter: validate and attach filter 437 * @flags: flags to change filter behavior 438 * @filter: seccomp filter to add to the current process 439 * 440 * Caller must be holding current->sighand->siglock lock. 441 * 442 * Returns 0 on success, -ve on error. 443 */ 444 static long seccomp_attach_filter(unsigned int flags, 445 struct seccomp_filter *filter) 446 { 447 unsigned long total_insns; 448 struct seccomp_filter *walker; 449 450 assert_spin_locked(¤t->sighand->siglock); 451 452 /* Validate resulting filter length. */ 453 total_insns = filter->prog->len; 454 for (walker = current->seccomp.filter; walker; walker = walker->prev) 455 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 456 if (total_insns > MAX_INSNS_PER_PATH) 457 return -ENOMEM; 458 459 /* If thread sync has been requested, check that it is possible. */ 460 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 461 int ret; 462 463 ret = seccomp_can_sync_threads(); 464 if (ret) 465 return ret; 466 } 467 468 /* Set log flag, if present. */ 469 if (flags & SECCOMP_FILTER_FLAG_LOG) 470 filter->log = true; 471 472 /* 473 * If there is an existing filter, make it the prev and don't drop its 474 * task reference. 475 */ 476 filter->prev = current->seccomp.filter; 477 current->seccomp.filter = filter; 478 479 /* Now that the new filter is in place, synchronize to all threads. */ 480 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 481 seccomp_sync_threads(flags); 482 483 return 0; 484 } 485 486 static void __get_seccomp_filter(struct seccomp_filter *filter) 487 { 488 /* Reference count is bounded by the number of total processes. */ 489 refcount_inc(&filter->usage); 490 } 491 492 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 493 void get_seccomp_filter(struct task_struct *tsk) 494 { 495 struct seccomp_filter *orig = tsk->seccomp.filter; 496 if (!orig) 497 return; 498 __get_seccomp_filter(orig); 499 } 500 501 static inline void seccomp_filter_free(struct seccomp_filter *filter) 502 { 503 if (filter) { 504 bpf_prog_destroy(filter->prog); 505 kfree(filter); 506 } 507 } 508 509 static void __put_seccomp_filter(struct seccomp_filter *orig) 510 { 511 /* Clean up single-reference branches iteratively. */ 512 while (orig && refcount_dec_and_test(&orig->usage)) { 513 struct seccomp_filter *freeme = orig; 514 orig = orig->prev; 515 seccomp_filter_free(freeme); 516 } 517 } 518 519 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 520 void put_seccomp_filter(struct task_struct *tsk) 521 { 522 __put_seccomp_filter(tsk->seccomp.filter); 523 } 524 525 static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason) 526 { 527 clear_siginfo(info); 528 info->si_signo = SIGSYS; 529 info->si_code = SYS_SECCOMP; 530 info->si_call_addr = (void __user *)KSTK_EIP(current); 531 info->si_errno = reason; 532 info->si_arch = syscall_get_arch(); 533 info->si_syscall = syscall; 534 } 535 536 /** 537 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 538 * @syscall: syscall number to send to userland 539 * @reason: filter-supplied reason code to send to userland (via si_errno) 540 * 541 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 542 */ 543 static void seccomp_send_sigsys(int syscall, int reason) 544 { 545 struct siginfo info; 546 seccomp_init_siginfo(&info, syscall, reason); 547 force_sig_info(SIGSYS, &info, current); 548 } 549 #endif /* CONFIG_SECCOMP_FILTER */ 550 551 /* For use with seccomp_actions_logged */ 552 #define SECCOMP_LOG_KILL_PROCESS (1 << 0) 553 #define SECCOMP_LOG_KILL_THREAD (1 << 1) 554 #define SECCOMP_LOG_TRAP (1 << 2) 555 #define SECCOMP_LOG_ERRNO (1 << 3) 556 #define SECCOMP_LOG_TRACE (1 << 4) 557 #define SECCOMP_LOG_LOG (1 << 5) 558 #define SECCOMP_LOG_ALLOW (1 << 6) 559 560 static u32 seccomp_actions_logged = SECCOMP_LOG_KILL_PROCESS | 561 SECCOMP_LOG_KILL_THREAD | 562 SECCOMP_LOG_TRAP | 563 SECCOMP_LOG_ERRNO | 564 SECCOMP_LOG_TRACE | 565 SECCOMP_LOG_LOG; 566 567 static inline void seccomp_log(unsigned long syscall, long signr, u32 action, 568 bool requested) 569 { 570 bool log = false; 571 572 switch (action) { 573 case SECCOMP_RET_ALLOW: 574 break; 575 case SECCOMP_RET_TRAP: 576 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRAP; 577 break; 578 case SECCOMP_RET_ERRNO: 579 log = requested && seccomp_actions_logged & SECCOMP_LOG_ERRNO; 580 break; 581 case SECCOMP_RET_TRACE: 582 log = requested && seccomp_actions_logged & SECCOMP_LOG_TRACE; 583 break; 584 case SECCOMP_RET_LOG: 585 log = seccomp_actions_logged & SECCOMP_LOG_LOG; 586 break; 587 case SECCOMP_RET_KILL_THREAD: 588 log = seccomp_actions_logged & SECCOMP_LOG_KILL_THREAD; 589 break; 590 case SECCOMP_RET_KILL_PROCESS: 591 default: 592 log = seccomp_actions_logged & SECCOMP_LOG_KILL_PROCESS; 593 } 594 595 /* 596 * Force an audit message to be emitted when the action is RET_KILL_*, 597 * RET_LOG, or the FILTER_FLAG_LOG bit was set and the action is 598 * allowed to be logged by the admin. 599 */ 600 if (log) 601 return __audit_seccomp(syscall, signr, action); 602 603 /* 604 * Let the audit subsystem decide if the action should be audited based 605 * on whether the current task itself is being audited. 606 */ 607 return audit_seccomp(syscall, signr, action); 608 } 609 610 /* 611 * Secure computing mode 1 allows only read/write/exit/sigreturn. 612 * To be fully secure this must be combined with rlimit 613 * to limit the stack allocations too. 614 */ 615 static const int mode1_syscalls[] = { 616 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 617 0, /* null terminated */ 618 }; 619 620 static void __secure_computing_strict(int this_syscall) 621 { 622 const int *syscall_whitelist = mode1_syscalls; 623 #ifdef CONFIG_COMPAT 624 if (in_compat_syscall()) 625 syscall_whitelist = get_compat_mode1_syscalls(); 626 #endif 627 do { 628 if (*syscall_whitelist == this_syscall) 629 return; 630 } while (*++syscall_whitelist); 631 632 #ifdef SECCOMP_DEBUG 633 dump_stack(); 634 #endif 635 seccomp_log(this_syscall, SIGKILL, SECCOMP_RET_KILL_THREAD, true); 636 do_exit(SIGKILL); 637 } 638 639 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 640 void secure_computing_strict(int this_syscall) 641 { 642 int mode = current->seccomp.mode; 643 644 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 645 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 646 return; 647 648 if (mode == SECCOMP_MODE_DISABLED) 649 return; 650 else if (mode == SECCOMP_MODE_STRICT) 651 __secure_computing_strict(this_syscall); 652 else 653 BUG(); 654 } 655 #else 656 657 #ifdef CONFIG_SECCOMP_FILTER 658 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 659 const bool recheck_after_trace) 660 { 661 u32 filter_ret, action; 662 struct seccomp_filter *match = NULL; 663 int data; 664 665 /* 666 * Make sure that any changes to mode from another thread have 667 * been seen after TIF_SECCOMP was seen. 668 */ 669 rmb(); 670 671 filter_ret = seccomp_run_filters(sd, &match); 672 data = filter_ret & SECCOMP_RET_DATA; 673 action = filter_ret & SECCOMP_RET_ACTION_FULL; 674 675 switch (action) { 676 case SECCOMP_RET_ERRNO: 677 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 678 if (data > MAX_ERRNO) 679 data = MAX_ERRNO; 680 syscall_set_return_value(current, task_pt_regs(current), 681 -data, 0); 682 goto skip; 683 684 case SECCOMP_RET_TRAP: 685 /* Show the handler the original registers. */ 686 syscall_rollback(current, task_pt_regs(current)); 687 /* Let the filter pass back 16 bits of data. */ 688 seccomp_send_sigsys(this_syscall, data); 689 goto skip; 690 691 case SECCOMP_RET_TRACE: 692 /* We've been put in this state by the ptracer already. */ 693 if (recheck_after_trace) 694 return 0; 695 696 /* ENOSYS these calls if there is no tracer attached. */ 697 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 698 syscall_set_return_value(current, 699 task_pt_regs(current), 700 -ENOSYS, 0); 701 goto skip; 702 } 703 704 /* Allow the BPF to provide the event message */ 705 ptrace_event(PTRACE_EVENT_SECCOMP, data); 706 /* 707 * The delivery of a fatal signal during event 708 * notification may silently skip tracer notification, 709 * which could leave us with a potentially unmodified 710 * syscall that the tracer would have liked to have 711 * changed. Since the process is about to die, we just 712 * force the syscall to be skipped and let the signal 713 * kill the process and correctly handle any tracer exit 714 * notifications. 715 */ 716 if (fatal_signal_pending(current)) 717 goto skip; 718 /* Check if the tracer forced the syscall to be skipped. */ 719 this_syscall = syscall_get_nr(current, task_pt_regs(current)); 720 if (this_syscall < 0) 721 goto skip; 722 723 /* 724 * Recheck the syscall, since it may have changed. This 725 * intentionally uses a NULL struct seccomp_data to force 726 * a reload of all registers. This does not goto skip since 727 * a skip would have already been reported. 728 */ 729 if (__seccomp_filter(this_syscall, NULL, true)) 730 return -1; 731 732 return 0; 733 734 case SECCOMP_RET_LOG: 735 seccomp_log(this_syscall, 0, action, true); 736 return 0; 737 738 case SECCOMP_RET_ALLOW: 739 /* 740 * Note that the "match" filter will always be NULL for 741 * this action since SECCOMP_RET_ALLOW is the starting 742 * state in seccomp_run_filters(). 743 */ 744 return 0; 745 746 case SECCOMP_RET_KILL_THREAD: 747 case SECCOMP_RET_KILL_PROCESS: 748 default: 749 seccomp_log(this_syscall, SIGSYS, action, true); 750 /* Dump core only if this is the last remaining thread. */ 751 if (action == SECCOMP_RET_KILL_PROCESS || 752 get_nr_threads(current) == 1) { 753 siginfo_t info; 754 755 /* Show the original registers in the dump. */ 756 syscall_rollback(current, task_pt_regs(current)); 757 /* Trigger a manual coredump since do_exit skips it. */ 758 seccomp_init_siginfo(&info, this_syscall, data); 759 do_coredump(&info); 760 } 761 if (action == SECCOMP_RET_KILL_PROCESS) 762 do_group_exit(SIGSYS); 763 else 764 do_exit(SIGSYS); 765 } 766 767 unreachable(); 768 769 skip: 770 seccomp_log(this_syscall, 0, action, match ? match->log : false); 771 return -1; 772 } 773 #else 774 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 775 const bool recheck_after_trace) 776 { 777 BUG(); 778 } 779 #endif 780 781 int __secure_computing(const struct seccomp_data *sd) 782 { 783 int mode = current->seccomp.mode; 784 int this_syscall; 785 786 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 787 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 788 return 0; 789 790 this_syscall = sd ? sd->nr : 791 syscall_get_nr(current, task_pt_regs(current)); 792 793 switch (mode) { 794 case SECCOMP_MODE_STRICT: 795 __secure_computing_strict(this_syscall); /* may call do_exit */ 796 return 0; 797 case SECCOMP_MODE_FILTER: 798 return __seccomp_filter(this_syscall, sd, false); 799 default: 800 BUG(); 801 } 802 } 803 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 804 805 long prctl_get_seccomp(void) 806 { 807 return current->seccomp.mode; 808 } 809 810 /** 811 * seccomp_set_mode_strict: internal function for setting strict seccomp 812 * 813 * Once current->seccomp.mode is non-zero, it may not be changed. 814 * 815 * Returns 0 on success or -EINVAL on failure. 816 */ 817 static long seccomp_set_mode_strict(void) 818 { 819 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 820 long ret = -EINVAL; 821 822 spin_lock_irq(¤t->sighand->siglock); 823 824 if (!seccomp_may_assign_mode(seccomp_mode)) 825 goto out; 826 827 #ifdef TIF_NOTSC 828 disable_TSC(); 829 #endif 830 seccomp_assign_mode(current, seccomp_mode, 0); 831 ret = 0; 832 833 out: 834 spin_unlock_irq(¤t->sighand->siglock); 835 836 return ret; 837 } 838 839 #ifdef CONFIG_SECCOMP_FILTER 840 /** 841 * seccomp_set_mode_filter: internal function for setting seccomp filter 842 * @flags: flags to change filter behavior 843 * @filter: struct sock_fprog containing filter 844 * 845 * This function may be called repeatedly to install additional filters. 846 * Every filter successfully installed will be evaluated (in reverse order) 847 * for each system call the task makes. 848 * 849 * Once current->seccomp.mode is non-zero, it may not be changed. 850 * 851 * Returns 0 on success or -EINVAL on failure. 852 */ 853 static long seccomp_set_mode_filter(unsigned int flags, 854 const char __user *filter) 855 { 856 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 857 struct seccomp_filter *prepared = NULL; 858 long ret = -EINVAL; 859 860 /* Validate flags. */ 861 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 862 return -EINVAL; 863 864 /* Prepare the new filter before holding any locks. */ 865 prepared = seccomp_prepare_user_filter(filter); 866 if (IS_ERR(prepared)) 867 return PTR_ERR(prepared); 868 869 /* 870 * Make sure we cannot change seccomp or nnp state via TSYNC 871 * while another thread is in the middle of calling exec. 872 */ 873 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 874 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 875 goto out_free; 876 877 spin_lock_irq(¤t->sighand->siglock); 878 879 if (!seccomp_may_assign_mode(seccomp_mode)) 880 goto out; 881 882 ret = seccomp_attach_filter(flags, prepared); 883 if (ret) 884 goto out; 885 /* Do not free the successfully attached filter. */ 886 prepared = NULL; 887 888 seccomp_assign_mode(current, seccomp_mode, flags); 889 out: 890 spin_unlock_irq(¤t->sighand->siglock); 891 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 892 mutex_unlock(¤t->signal->cred_guard_mutex); 893 out_free: 894 seccomp_filter_free(prepared); 895 return ret; 896 } 897 #else 898 static inline long seccomp_set_mode_filter(unsigned int flags, 899 const char __user *filter) 900 { 901 return -EINVAL; 902 } 903 #endif 904 905 static long seccomp_get_action_avail(const char __user *uaction) 906 { 907 u32 action; 908 909 if (copy_from_user(&action, uaction, sizeof(action))) 910 return -EFAULT; 911 912 switch (action) { 913 case SECCOMP_RET_KILL_PROCESS: 914 case SECCOMP_RET_KILL_THREAD: 915 case SECCOMP_RET_TRAP: 916 case SECCOMP_RET_ERRNO: 917 case SECCOMP_RET_TRACE: 918 case SECCOMP_RET_LOG: 919 case SECCOMP_RET_ALLOW: 920 break; 921 default: 922 return -EOPNOTSUPP; 923 } 924 925 return 0; 926 } 927 928 /* Common entry point for both prctl and syscall. */ 929 static long do_seccomp(unsigned int op, unsigned int flags, 930 const char __user *uargs) 931 { 932 switch (op) { 933 case SECCOMP_SET_MODE_STRICT: 934 if (flags != 0 || uargs != NULL) 935 return -EINVAL; 936 return seccomp_set_mode_strict(); 937 case SECCOMP_SET_MODE_FILTER: 938 return seccomp_set_mode_filter(flags, uargs); 939 case SECCOMP_GET_ACTION_AVAIL: 940 if (flags != 0) 941 return -EINVAL; 942 943 return seccomp_get_action_avail(uargs); 944 default: 945 return -EINVAL; 946 } 947 } 948 949 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 950 const char __user *, uargs) 951 { 952 return do_seccomp(op, flags, uargs); 953 } 954 955 /** 956 * prctl_set_seccomp: configures current->seccomp.mode 957 * @seccomp_mode: requested mode to use 958 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 959 * 960 * Returns 0 on success or -EINVAL on failure. 961 */ 962 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 963 { 964 unsigned int op; 965 char __user *uargs; 966 967 switch (seccomp_mode) { 968 case SECCOMP_MODE_STRICT: 969 op = SECCOMP_SET_MODE_STRICT; 970 /* 971 * Setting strict mode through prctl always ignored filter, 972 * so make sure it is always NULL here to pass the internal 973 * check in do_seccomp(). 974 */ 975 uargs = NULL; 976 break; 977 case SECCOMP_MODE_FILTER: 978 op = SECCOMP_SET_MODE_FILTER; 979 uargs = filter; 980 break; 981 default: 982 return -EINVAL; 983 } 984 985 /* prctl interface doesn't have flags, so they are always zero. */ 986 return do_seccomp(op, 0, uargs); 987 } 988 989 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) 990 static struct seccomp_filter *get_nth_filter(struct task_struct *task, 991 unsigned long filter_off) 992 { 993 struct seccomp_filter *orig, *filter; 994 unsigned long count; 995 996 /* 997 * Note: this is only correct because the caller should be the (ptrace) 998 * tracer of the task, otherwise lock_task_sighand is needed. 999 */ 1000 spin_lock_irq(&task->sighand->siglock); 1001 1002 if (task->seccomp.mode != SECCOMP_MODE_FILTER) { 1003 spin_unlock_irq(&task->sighand->siglock); 1004 return ERR_PTR(-EINVAL); 1005 } 1006 1007 orig = task->seccomp.filter; 1008 __get_seccomp_filter(orig); 1009 spin_unlock_irq(&task->sighand->siglock); 1010 1011 count = 0; 1012 for (filter = orig; filter; filter = filter->prev) 1013 count++; 1014 1015 if (filter_off >= count) { 1016 filter = ERR_PTR(-ENOENT); 1017 goto out; 1018 } 1019 1020 count -= filter_off; 1021 for (filter = orig; filter && count > 1; filter = filter->prev) 1022 count--; 1023 1024 if (WARN_ON(count != 1 || !filter)) { 1025 filter = ERR_PTR(-ENOENT); 1026 goto out; 1027 } 1028 1029 __get_seccomp_filter(filter); 1030 1031 out: 1032 __put_seccomp_filter(orig); 1033 return filter; 1034 } 1035 1036 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, 1037 void __user *data) 1038 { 1039 struct seccomp_filter *filter; 1040 struct sock_fprog_kern *fprog; 1041 long ret; 1042 1043 if (!capable(CAP_SYS_ADMIN) || 1044 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 1045 return -EACCES; 1046 } 1047 1048 filter = get_nth_filter(task, filter_off); 1049 if (IS_ERR(filter)) 1050 return PTR_ERR(filter); 1051 1052 fprog = filter->prog->orig_prog; 1053 if (!fprog) { 1054 /* This must be a new non-cBPF filter, since we save 1055 * every cBPF filter's orig_prog above when 1056 * CONFIG_CHECKPOINT_RESTORE is enabled. 1057 */ 1058 ret = -EMEDIUMTYPE; 1059 goto out; 1060 } 1061 1062 ret = fprog->len; 1063 if (!data) 1064 goto out; 1065 1066 if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) 1067 ret = -EFAULT; 1068 1069 out: 1070 __put_seccomp_filter(filter); 1071 return ret; 1072 } 1073 1074 long seccomp_get_metadata(struct task_struct *task, 1075 unsigned long size, void __user *data) 1076 { 1077 long ret; 1078 struct seccomp_filter *filter; 1079 struct seccomp_metadata kmd = {}; 1080 1081 if (!capable(CAP_SYS_ADMIN) || 1082 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 1083 return -EACCES; 1084 } 1085 1086 size = min_t(unsigned long, size, sizeof(kmd)); 1087 1088 if (size < sizeof(kmd.filter_off)) 1089 return -EINVAL; 1090 1091 if (copy_from_user(&kmd.filter_off, data, sizeof(kmd.filter_off))) 1092 return -EFAULT; 1093 1094 filter = get_nth_filter(task, kmd.filter_off); 1095 if (IS_ERR(filter)) 1096 return PTR_ERR(filter); 1097 1098 if (filter->log) 1099 kmd.flags |= SECCOMP_FILTER_FLAG_LOG; 1100 1101 ret = size; 1102 if (copy_to_user(data, &kmd, size)) 1103 ret = -EFAULT; 1104 1105 __put_seccomp_filter(filter); 1106 return ret; 1107 } 1108 #endif 1109 1110 #ifdef CONFIG_SYSCTL 1111 1112 /* Human readable action names for friendly sysctl interaction */ 1113 #define SECCOMP_RET_KILL_PROCESS_NAME "kill_process" 1114 #define SECCOMP_RET_KILL_THREAD_NAME "kill_thread" 1115 #define SECCOMP_RET_TRAP_NAME "trap" 1116 #define SECCOMP_RET_ERRNO_NAME "errno" 1117 #define SECCOMP_RET_TRACE_NAME "trace" 1118 #define SECCOMP_RET_LOG_NAME "log" 1119 #define SECCOMP_RET_ALLOW_NAME "allow" 1120 1121 static const char seccomp_actions_avail[] = 1122 SECCOMP_RET_KILL_PROCESS_NAME " " 1123 SECCOMP_RET_KILL_THREAD_NAME " " 1124 SECCOMP_RET_TRAP_NAME " " 1125 SECCOMP_RET_ERRNO_NAME " " 1126 SECCOMP_RET_TRACE_NAME " " 1127 SECCOMP_RET_LOG_NAME " " 1128 SECCOMP_RET_ALLOW_NAME; 1129 1130 struct seccomp_log_name { 1131 u32 log; 1132 const char *name; 1133 }; 1134 1135 static const struct seccomp_log_name seccomp_log_names[] = { 1136 { SECCOMP_LOG_KILL_PROCESS, SECCOMP_RET_KILL_PROCESS_NAME }, 1137 { SECCOMP_LOG_KILL_THREAD, SECCOMP_RET_KILL_THREAD_NAME }, 1138 { SECCOMP_LOG_TRAP, SECCOMP_RET_TRAP_NAME }, 1139 { SECCOMP_LOG_ERRNO, SECCOMP_RET_ERRNO_NAME }, 1140 { SECCOMP_LOG_TRACE, SECCOMP_RET_TRACE_NAME }, 1141 { SECCOMP_LOG_LOG, SECCOMP_RET_LOG_NAME }, 1142 { SECCOMP_LOG_ALLOW, SECCOMP_RET_ALLOW_NAME }, 1143 { } 1144 }; 1145 1146 static bool seccomp_names_from_actions_logged(char *names, size_t size, 1147 u32 actions_logged) 1148 { 1149 const struct seccomp_log_name *cur; 1150 bool append_space = false; 1151 1152 for (cur = seccomp_log_names; cur->name && size; cur++) { 1153 ssize_t ret; 1154 1155 if (!(actions_logged & cur->log)) 1156 continue; 1157 1158 if (append_space) { 1159 ret = strscpy(names, " ", size); 1160 if (ret < 0) 1161 return false; 1162 1163 names += ret; 1164 size -= ret; 1165 } else 1166 append_space = true; 1167 1168 ret = strscpy(names, cur->name, size); 1169 if (ret < 0) 1170 return false; 1171 1172 names += ret; 1173 size -= ret; 1174 } 1175 1176 return true; 1177 } 1178 1179 static bool seccomp_action_logged_from_name(u32 *action_logged, 1180 const char *name) 1181 { 1182 const struct seccomp_log_name *cur; 1183 1184 for (cur = seccomp_log_names; cur->name; cur++) { 1185 if (!strcmp(cur->name, name)) { 1186 *action_logged = cur->log; 1187 return true; 1188 } 1189 } 1190 1191 return false; 1192 } 1193 1194 static bool seccomp_actions_logged_from_names(u32 *actions_logged, char *names) 1195 { 1196 char *name; 1197 1198 *actions_logged = 0; 1199 while ((name = strsep(&names, " ")) && *name) { 1200 u32 action_logged = 0; 1201 1202 if (!seccomp_action_logged_from_name(&action_logged, name)) 1203 return false; 1204 1205 *actions_logged |= action_logged; 1206 } 1207 1208 return true; 1209 } 1210 1211 static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write, 1212 void __user *buffer, size_t *lenp, 1213 loff_t *ppos) 1214 { 1215 char names[sizeof(seccomp_actions_avail)]; 1216 struct ctl_table table; 1217 int ret; 1218 1219 if (write && !capable(CAP_SYS_ADMIN)) 1220 return -EPERM; 1221 1222 memset(names, 0, sizeof(names)); 1223 1224 if (!write) { 1225 if (!seccomp_names_from_actions_logged(names, sizeof(names), 1226 seccomp_actions_logged)) 1227 return -EINVAL; 1228 } 1229 1230 table = *ro_table; 1231 table.data = names; 1232 table.maxlen = sizeof(names); 1233 ret = proc_dostring(&table, write, buffer, lenp, ppos); 1234 if (ret) 1235 return ret; 1236 1237 if (write) { 1238 u32 actions_logged; 1239 1240 if (!seccomp_actions_logged_from_names(&actions_logged, 1241 table.data)) 1242 return -EINVAL; 1243 1244 if (actions_logged & SECCOMP_LOG_ALLOW) 1245 return -EINVAL; 1246 1247 seccomp_actions_logged = actions_logged; 1248 } 1249 1250 return 0; 1251 } 1252 1253 static struct ctl_path seccomp_sysctl_path[] = { 1254 { .procname = "kernel", }, 1255 { .procname = "seccomp", }, 1256 { } 1257 }; 1258 1259 static struct ctl_table seccomp_sysctl_table[] = { 1260 { 1261 .procname = "actions_avail", 1262 .data = (void *) &seccomp_actions_avail, 1263 .maxlen = sizeof(seccomp_actions_avail), 1264 .mode = 0444, 1265 .proc_handler = proc_dostring, 1266 }, 1267 { 1268 .procname = "actions_logged", 1269 .mode = 0644, 1270 .proc_handler = seccomp_actions_logged_handler, 1271 }, 1272 { } 1273 }; 1274 1275 static int __init seccomp_sysctl_init(void) 1276 { 1277 struct ctl_table_header *hdr; 1278 1279 hdr = register_sysctl_paths(seccomp_sysctl_path, seccomp_sysctl_table); 1280 if (!hdr) 1281 pr_warn("seccomp: sysctl registration failed\n"); 1282 else 1283 kmemleak_not_leak(hdr); 1284 1285 return 0; 1286 } 1287 1288 device_initcall(seccomp_sysctl_init) 1289 1290 #endif /* CONFIG_SYSCTL */ 1291