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/atomic.h> 17 #include <linux/audit.h> 18 #include <linux/compat.h> 19 #include <linux/sched.h> 20 #include <linux/seccomp.h> 21 #include <linux/slab.h> 22 #include <linux/syscalls.h> 23 24 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER 25 #include <asm/syscall.h> 26 #endif 27 28 #ifdef CONFIG_SECCOMP_FILTER 29 #include <linux/filter.h> 30 #include <linux/pid.h> 31 #include <linux/ptrace.h> 32 #include <linux/security.h> 33 #include <linux/tracehook.h> 34 #include <linux/uaccess.h> 35 36 /** 37 * struct seccomp_filter - container for seccomp BPF programs 38 * 39 * @usage: reference count to manage the object lifetime. 40 * get/put helpers should be used when accessing an instance 41 * outside of a lifetime-guarded section. In general, this 42 * is only needed for handling filters shared across tasks. 43 * @prev: points to a previously installed, or inherited, filter 44 * @len: the number of instructions in the program 45 * @insnsi: the BPF program instructions to evaluate 46 * 47 * seccomp_filter objects are organized in a tree linked via the @prev 48 * pointer. For any task, it appears to be a singly-linked list starting 49 * with current->seccomp.filter, the most recently attached or inherited filter. 50 * However, multiple filters may share a @prev node, by way of fork(), which 51 * results in a unidirectional tree existing in memory. This is similar to 52 * how namespaces work. 53 * 54 * seccomp_filter objects should never be modified after being attached 55 * to a task_struct (other than @usage). 56 */ 57 struct seccomp_filter { 58 atomic_t usage; 59 struct seccomp_filter *prev; 60 struct bpf_prog *prog; 61 }; 62 63 /* Limit any path through the tree to 256KB worth of instructions. */ 64 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter)) 65 66 /* 67 * Endianness is explicitly ignored and left for BPF program authors to manage 68 * as per the specific architecture. 69 */ 70 static void populate_seccomp_data(struct seccomp_data *sd) 71 { 72 struct task_struct *task = current; 73 struct pt_regs *regs = task_pt_regs(task); 74 unsigned long args[6]; 75 76 sd->nr = syscall_get_nr(task, regs); 77 sd->arch = syscall_get_arch(); 78 syscall_get_arguments(task, regs, 0, 6, args); 79 sd->args[0] = args[0]; 80 sd->args[1] = args[1]; 81 sd->args[2] = args[2]; 82 sd->args[3] = args[3]; 83 sd->args[4] = args[4]; 84 sd->args[5] = args[5]; 85 sd->instruction_pointer = KSTK_EIP(task); 86 } 87 88 /** 89 * seccomp_check_filter - verify seccomp filter code 90 * @filter: filter to verify 91 * @flen: length of filter 92 * 93 * Takes a previously checked filter (by bpf_check_classic) and 94 * redirects all filter code that loads struct sk_buff data 95 * and related data through seccomp_bpf_load. It also 96 * enforces length and alignment checking of those loads. 97 * 98 * Returns 0 if the rule set is legal or -EINVAL if not. 99 */ 100 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) 101 { 102 int pc; 103 for (pc = 0; pc < flen; pc++) { 104 struct sock_filter *ftest = &filter[pc]; 105 u16 code = ftest->code; 106 u32 k = ftest->k; 107 108 switch (code) { 109 case BPF_LD | BPF_W | BPF_ABS: 110 ftest->code = BPF_LDX | BPF_W | BPF_ABS; 111 /* 32-bit aligned and not out of bounds. */ 112 if (k >= sizeof(struct seccomp_data) || k & 3) 113 return -EINVAL; 114 continue; 115 case BPF_LD | BPF_W | BPF_LEN: 116 ftest->code = BPF_LD | BPF_IMM; 117 ftest->k = sizeof(struct seccomp_data); 118 continue; 119 case BPF_LDX | BPF_W | BPF_LEN: 120 ftest->code = BPF_LDX | BPF_IMM; 121 ftest->k = sizeof(struct seccomp_data); 122 continue; 123 /* Explicitly include allowed calls. */ 124 case BPF_RET | BPF_K: 125 case BPF_RET | BPF_A: 126 case BPF_ALU | BPF_ADD | BPF_K: 127 case BPF_ALU | BPF_ADD | BPF_X: 128 case BPF_ALU | BPF_SUB | BPF_K: 129 case BPF_ALU | BPF_SUB | BPF_X: 130 case BPF_ALU | BPF_MUL | BPF_K: 131 case BPF_ALU | BPF_MUL | BPF_X: 132 case BPF_ALU | BPF_DIV | BPF_K: 133 case BPF_ALU | BPF_DIV | BPF_X: 134 case BPF_ALU | BPF_AND | BPF_K: 135 case BPF_ALU | BPF_AND | BPF_X: 136 case BPF_ALU | BPF_OR | BPF_K: 137 case BPF_ALU | BPF_OR | BPF_X: 138 case BPF_ALU | BPF_XOR | BPF_K: 139 case BPF_ALU | BPF_XOR | BPF_X: 140 case BPF_ALU | BPF_LSH | BPF_K: 141 case BPF_ALU | BPF_LSH | BPF_X: 142 case BPF_ALU | BPF_RSH | BPF_K: 143 case BPF_ALU | BPF_RSH | BPF_X: 144 case BPF_ALU | BPF_NEG: 145 case BPF_LD | BPF_IMM: 146 case BPF_LDX | BPF_IMM: 147 case BPF_MISC | BPF_TAX: 148 case BPF_MISC | BPF_TXA: 149 case BPF_LD | BPF_MEM: 150 case BPF_LDX | BPF_MEM: 151 case BPF_ST: 152 case BPF_STX: 153 case BPF_JMP | BPF_JA: 154 case BPF_JMP | BPF_JEQ | BPF_K: 155 case BPF_JMP | BPF_JEQ | BPF_X: 156 case BPF_JMP | BPF_JGE | BPF_K: 157 case BPF_JMP | BPF_JGE | BPF_X: 158 case BPF_JMP | BPF_JGT | BPF_K: 159 case BPF_JMP | BPF_JGT | BPF_X: 160 case BPF_JMP | BPF_JSET | BPF_K: 161 case BPF_JMP | BPF_JSET | BPF_X: 162 continue; 163 default: 164 return -EINVAL; 165 } 166 } 167 return 0; 168 } 169 170 /** 171 * seccomp_run_filters - evaluates all seccomp filters against @syscall 172 * @syscall: number of the current system call 173 * 174 * Returns valid seccomp BPF response codes. 175 */ 176 static u32 seccomp_run_filters(struct seccomp_data *sd) 177 { 178 struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter); 179 struct seccomp_data sd_local; 180 u32 ret = SECCOMP_RET_ALLOW; 181 182 /* Ensure unexpected behavior doesn't result in failing open. */ 183 if (unlikely(WARN_ON(f == NULL))) 184 return SECCOMP_RET_KILL; 185 186 /* Make sure cross-thread synced filter points somewhere sane. */ 187 smp_read_barrier_depends(); 188 189 if (!sd) { 190 populate_seccomp_data(&sd_local); 191 sd = &sd_local; 192 } 193 194 /* 195 * All filters in the list are evaluated and the lowest BPF return 196 * value always takes priority (ignoring the DATA). 197 */ 198 for (; f; f = f->prev) { 199 u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd); 200 201 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION)) 202 ret = cur_ret; 203 } 204 return ret; 205 } 206 #endif /* CONFIG_SECCOMP_FILTER */ 207 208 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 209 { 210 assert_spin_locked(¤t->sighand->siglock); 211 212 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) 213 return false; 214 215 return true; 216 } 217 218 static inline void seccomp_assign_mode(struct task_struct *task, 219 unsigned long seccomp_mode) 220 { 221 assert_spin_locked(&task->sighand->siglock); 222 223 task->seccomp.mode = seccomp_mode; 224 /* 225 * Make sure TIF_SECCOMP cannot be set before the mode (and 226 * filter) is set. 227 */ 228 smp_mb__before_atomic(); 229 set_tsk_thread_flag(task, TIF_SECCOMP); 230 } 231 232 #ifdef CONFIG_SECCOMP_FILTER 233 /* Returns 1 if the parent is an ancestor of the child. */ 234 static int is_ancestor(struct seccomp_filter *parent, 235 struct seccomp_filter *child) 236 { 237 /* NULL is the root ancestor. */ 238 if (parent == NULL) 239 return 1; 240 for (; child; child = child->prev) 241 if (child == parent) 242 return 1; 243 return 0; 244 } 245 246 /** 247 * seccomp_can_sync_threads: checks if all threads can be synchronized 248 * 249 * Expects sighand and cred_guard_mutex locks to be held. 250 * 251 * Returns 0 on success, -ve on error, or the pid of a thread which was 252 * either not in the correct seccomp mode or it did not have an ancestral 253 * seccomp filter. 254 */ 255 static inline pid_t seccomp_can_sync_threads(void) 256 { 257 struct task_struct *thread, *caller; 258 259 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 260 assert_spin_locked(¤t->sighand->siglock); 261 262 /* Validate all threads being eligible for synchronization. */ 263 caller = current; 264 for_each_thread(caller, thread) { 265 pid_t failed; 266 267 /* Skip current, since it is initiating the sync. */ 268 if (thread == caller) 269 continue; 270 271 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || 272 (thread->seccomp.mode == SECCOMP_MODE_FILTER && 273 is_ancestor(thread->seccomp.filter, 274 caller->seccomp.filter))) 275 continue; 276 277 /* Return the first thread that cannot be synchronized. */ 278 failed = task_pid_vnr(thread); 279 /* If the pid cannot be resolved, then return -ESRCH */ 280 if (unlikely(WARN_ON(failed == 0))) 281 failed = -ESRCH; 282 return failed; 283 } 284 285 return 0; 286 } 287 288 /** 289 * seccomp_sync_threads: sets all threads to use current's filter 290 * 291 * Expects sighand and cred_guard_mutex locks to be held, and for 292 * seccomp_can_sync_threads() to have returned success already 293 * without dropping the locks. 294 * 295 */ 296 static inline void seccomp_sync_threads(void) 297 { 298 struct task_struct *thread, *caller; 299 300 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 301 assert_spin_locked(¤t->sighand->siglock); 302 303 /* Synchronize all threads. */ 304 caller = current; 305 for_each_thread(caller, thread) { 306 /* Skip current, since it needs no changes. */ 307 if (thread == caller) 308 continue; 309 310 /* Get a task reference for the new leaf node. */ 311 get_seccomp_filter(caller); 312 /* 313 * Drop the task reference to the shared ancestor since 314 * current's path will hold a reference. (This also 315 * allows a put before the assignment.) 316 */ 317 put_seccomp_filter(thread); 318 smp_store_release(&thread->seccomp.filter, 319 caller->seccomp.filter); 320 /* 321 * Opt the other thread into seccomp if needed. 322 * As threads are considered to be trust-realm 323 * equivalent (see ptrace_may_access), it is safe to 324 * allow one thread to transition the other. 325 */ 326 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) { 327 /* 328 * Don't let an unprivileged task work around 329 * the no_new_privs restriction by creating 330 * a thread that sets it up, enters seccomp, 331 * then dies. 332 */ 333 if (task_no_new_privs(caller)) 334 task_set_no_new_privs(thread); 335 336 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 337 } 338 } 339 } 340 341 /** 342 * seccomp_prepare_filter: Prepares a seccomp filter for use. 343 * @fprog: BPF program to install 344 * 345 * Returns filter on success or an ERR_PTR on failure. 346 */ 347 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 348 { 349 struct seccomp_filter *sfilter; 350 int ret; 351 352 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 353 return ERR_PTR(-EINVAL); 354 355 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 356 357 /* 358 * Installing a seccomp filter requires that the task has 359 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 360 * This avoids scenarios where unprivileged tasks can affect the 361 * behavior of privileged children. 362 */ 363 if (!task_no_new_privs(current) && 364 security_capable_noaudit(current_cred(), current_user_ns(), 365 CAP_SYS_ADMIN) != 0) 366 return ERR_PTR(-EACCES); 367 368 /* Allocate a new seccomp_filter */ 369 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); 370 if (!sfilter) 371 return ERR_PTR(-ENOMEM); 372 373 ret = bpf_prog_create_from_user(&sfilter->prog, fprog, 374 seccomp_check_filter); 375 if (ret < 0) { 376 kfree(sfilter); 377 return ERR_PTR(ret); 378 } 379 380 atomic_set(&sfilter->usage, 1); 381 382 return sfilter; 383 } 384 385 /** 386 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 387 * @user_filter: pointer to the user data containing a sock_fprog. 388 * 389 * Returns 0 on success and non-zero otherwise. 390 */ 391 static struct seccomp_filter * 392 seccomp_prepare_user_filter(const char __user *user_filter) 393 { 394 struct sock_fprog fprog; 395 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 396 397 #ifdef CONFIG_COMPAT 398 if (is_compat_task()) { 399 struct compat_sock_fprog fprog32; 400 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 401 goto out; 402 fprog.len = fprog32.len; 403 fprog.filter = compat_ptr(fprog32.filter); 404 } else /* falls through to the if below. */ 405 #endif 406 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 407 goto out; 408 filter = seccomp_prepare_filter(&fprog); 409 out: 410 return filter; 411 } 412 413 /** 414 * seccomp_attach_filter: validate and attach filter 415 * @flags: flags to change filter behavior 416 * @filter: seccomp filter to add to the current process 417 * 418 * Caller must be holding current->sighand->siglock lock. 419 * 420 * Returns 0 on success, -ve on error. 421 */ 422 static long seccomp_attach_filter(unsigned int flags, 423 struct seccomp_filter *filter) 424 { 425 unsigned long total_insns; 426 struct seccomp_filter *walker; 427 428 assert_spin_locked(¤t->sighand->siglock); 429 430 /* Validate resulting filter length. */ 431 total_insns = filter->prog->len; 432 for (walker = current->seccomp.filter; walker; walker = walker->prev) 433 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 434 if (total_insns > MAX_INSNS_PER_PATH) 435 return -ENOMEM; 436 437 /* If thread sync has been requested, check that it is possible. */ 438 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 439 int ret; 440 441 ret = seccomp_can_sync_threads(); 442 if (ret) 443 return ret; 444 } 445 446 /* 447 * If there is an existing filter, make it the prev and don't drop its 448 * task reference. 449 */ 450 filter->prev = current->seccomp.filter; 451 current->seccomp.filter = filter; 452 453 /* Now that the new filter is in place, synchronize to all threads. */ 454 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 455 seccomp_sync_threads(); 456 457 return 0; 458 } 459 460 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 461 void get_seccomp_filter(struct task_struct *tsk) 462 { 463 struct seccomp_filter *orig = tsk->seccomp.filter; 464 if (!orig) 465 return; 466 /* Reference count is bounded by the number of total processes. */ 467 atomic_inc(&orig->usage); 468 } 469 470 static inline void seccomp_filter_free(struct seccomp_filter *filter) 471 { 472 if (filter) { 473 bpf_prog_free(filter->prog); 474 kfree(filter); 475 } 476 } 477 478 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 479 void put_seccomp_filter(struct task_struct *tsk) 480 { 481 struct seccomp_filter *orig = tsk->seccomp.filter; 482 /* Clean up single-reference branches iteratively. */ 483 while (orig && atomic_dec_and_test(&orig->usage)) { 484 struct seccomp_filter *freeme = orig; 485 orig = orig->prev; 486 seccomp_filter_free(freeme); 487 } 488 } 489 490 /** 491 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 492 * @syscall: syscall number to send to userland 493 * @reason: filter-supplied reason code to send to userland (via si_errno) 494 * 495 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 496 */ 497 static void seccomp_send_sigsys(int syscall, int reason) 498 { 499 struct siginfo info; 500 memset(&info, 0, sizeof(info)); 501 info.si_signo = SIGSYS; 502 info.si_code = SYS_SECCOMP; 503 info.si_call_addr = (void __user *)KSTK_EIP(current); 504 info.si_errno = reason; 505 info.si_arch = syscall_get_arch(); 506 info.si_syscall = syscall; 507 force_sig_info(SIGSYS, &info, current); 508 } 509 #endif /* CONFIG_SECCOMP_FILTER */ 510 511 /* 512 * Secure computing mode 1 allows only read/write/exit/sigreturn. 513 * To be fully secure this must be combined with rlimit 514 * to limit the stack allocations too. 515 */ 516 static int mode1_syscalls[] = { 517 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 518 0, /* null terminated */ 519 }; 520 521 #ifdef CONFIG_COMPAT 522 static int mode1_syscalls_32[] = { 523 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32, 524 0, /* null terminated */ 525 }; 526 #endif 527 528 static void __secure_computing_strict(int this_syscall) 529 { 530 int *syscall_whitelist = mode1_syscalls; 531 #ifdef CONFIG_COMPAT 532 if (is_compat_task()) 533 syscall_whitelist = mode1_syscalls_32; 534 #endif 535 do { 536 if (*syscall_whitelist == this_syscall) 537 return; 538 } while (*++syscall_whitelist); 539 540 #ifdef SECCOMP_DEBUG 541 dump_stack(); 542 #endif 543 audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL); 544 do_exit(SIGKILL); 545 } 546 547 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 548 void secure_computing_strict(int this_syscall) 549 { 550 int mode = current->seccomp.mode; 551 552 if (mode == 0) 553 return; 554 else if (mode == SECCOMP_MODE_STRICT) 555 __secure_computing_strict(this_syscall); 556 else 557 BUG(); 558 } 559 #else 560 int __secure_computing(void) 561 { 562 u32 phase1_result = seccomp_phase1(NULL); 563 564 if (likely(phase1_result == SECCOMP_PHASE1_OK)) 565 return 0; 566 else if (likely(phase1_result == SECCOMP_PHASE1_SKIP)) 567 return -1; 568 else 569 return seccomp_phase2(phase1_result); 570 } 571 572 #ifdef CONFIG_SECCOMP_FILTER 573 static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd) 574 { 575 u32 filter_ret, action; 576 int data; 577 578 /* 579 * Make sure that any changes to mode from another thread have 580 * been seen after TIF_SECCOMP was seen. 581 */ 582 rmb(); 583 584 filter_ret = seccomp_run_filters(sd); 585 data = filter_ret & SECCOMP_RET_DATA; 586 action = filter_ret & SECCOMP_RET_ACTION; 587 588 switch (action) { 589 case SECCOMP_RET_ERRNO: 590 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 591 if (data > MAX_ERRNO) 592 data = MAX_ERRNO; 593 syscall_set_return_value(current, task_pt_regs(current), 594 -data, 0); 595 goto skip; 596 597 case SECCOMP_RET_TRAP: 598 /* Show the handler the original registers. */ 599 syscall_rollback(current, task_pt_regs(current)); 600 /* Let the filter pass back 16 bits of data. */ 601 seccomp_send_sigsys(this_syscall, data); 602 goto skip; 603 604 case SECCOMP_RET_TRACE: 605 return filter_ret; /* Save the rest for phase 2. */ 606 607 case SECCOMP_RET_ALLOW: 608 return SECCOMP_PHASE1_OK; 609 610 case SECCOMP_RET_KILL: 611 default: 612 audit_seccomp(this_syscall, SIGSYS, action); 613 do_exit(SIGSYS); 614 } 615 616 unreachable(); 617 618 skip: 619 audit_seccomp(this_syscall, 0, action); 620 return SECCOMP_PHASE1_SKIP; 621 } 622 #endif 623 624 /** 625 * seccomp_phase1() - run fast path seccomp checks on the current syscall 626 * @arg sd: The seccomp_data or NULL 627 * 628 * This only reads pt_regs via the syscall_xyz helpers. The only change 629 * it will make to pt_regs is via syscall_set_return_value, and it will 630 * only do that if it returns SECCOMP_PHASE1_SKIP. 631 * 632 * If sd is provided, it will not read pt_regs at all. 633 * 634 * It may also call do_exit or force a signal; these actions must be 635 * safe. 636 * 637 * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should 638 * be processed normally. 639 * 640 * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be 641 * invoked. In this case, seccomp_phase1 will have set the return value 642 * using syscall_set_return_value. 643 * 644 * If it returns anything else, then the return value should be passed 645 * to seccomp_phase2 from a context in which ptrace hooks are safe. 646 */ 647 u32 seccomp_phase1(struct seccomp_data *sd) 648 { 649 int mode = current->seccomp.mode; 650 int this_syscall = sd ? sd->nr : 651 syscall_get_nr(current, task_pt_regs(current)); 652 653 switch (mode) { 654 case SECCOMP_MODE_STRICT: 655 __secure_computing_strict(this_syscall); /* may call do_exit */ 656 return SECCOMP_PHASE1_OK; 657 #ifdef CONFIG_SECCOMP_FILTER 658 case SECCOMP_MODE_FILTER: 659 return __seccomp_phase1_filter(this_syscall, sd); 660 #endif 661 default: 662 BUG(); 663 } 664 } 665 666 /** 667 * seccomp_phase2() - finish slow path seccomp work for the current syscall 668 * @phase1_result: The return value from seccomp_phase1() 669 * 670 * This must be called from a context in which ptrace hooks can be used. 671 * 672 * Returns 0 if the syscall should be processed or -1 to skip the syscall. 673 */ 674 int seccomp_phase2(u32 phase1_result) 675 { 676 struct pt_regs *regs = task_pt_regs(current); 677 u32 action = phase1_result & SECCOMP_RET_ACTION; 678 int data = phase1_result & SECCOMP_RET_DATA; 679 680 BUG_ON(action != SECCOMP_RET_TRACE); 681 682 audit_seccomp(syscall_get_nr(current, regs), 0, action); 683 684 /* Skip these calls if there is no tracer. */ 685 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 686 syscall_set_return_value(current, regs, 687 -ENOSYS, 0); 688 return -1; 689 } 690 691 /* Allow the BPF to provide the event message */ 692 ptrace_event(PTRACE_EVENT_SECCOMP, data); 693 /* 694 * The delivery of a fatal signal during event 695 * notification may silently skip tracer notification. 696 * Terminating the task now avoids executing a system 697 * call that may not be intended. 698 */ 699 if (fatal_signal_pending(current)) 700 do_exit(SIGSYS); 701 if (syscall_get_nr(current, regs) < 0) 702 return -1; /* Explicit request to skip. */ 703 704 return 0; 705 } 706 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 707 708 long prctl_get_seccomp(void) 709 { 710 return current->seccomp.mode; 711 } 712 713 /** 714 * seccomp_set_mode_strict: internal function for setting strict seccomp 715 * 716 * Once current->seccomp.mode is non-zero, it may not be changed. 717 * 718 * Returns 0 on success or -EINVAL on failure. 719 */ 720 static long seccomp_set_mode_strict(void) 721 { 722 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 723 long ret = -EINVAL; 724 725 spin_lock_irq(¤t->sighand->siglock); 726 727 if (!seccomp_may_assign_mode(seccomp_mode)) 728 goto out; 729 730 #ifdef TIF_NOTSC 731 disable_TSC(); 732 #endif 733 seccomp_assign_mode(current, seccomp_mode); 734 ret = 0; 735 736 out: 737 spin_unlock_irq(¤t->sighand->siglock); 738 739 return ret; 740 } 741 742 #ifdef CONFIG_SECCOMP_FILTER 743 /** 744 * seccomp_set_mode_filter: internal function for setting seccomp filter 745 * @flags: flags to change filter behavior 746 * @filter: struct sock_fprog containing filter 747 * 748 * This function may be called repeatedly to install additional filters. 749 * Every filter successfully installed will be evaluated (in reverse order) 750 * for each system call the task makes. 751 * 752 * Once current->seccomp.mode is non-zero, it may not be changed. 753 * 754 * Returns 0 on success or -EINVAL on failure. 755 */ 756 static long seccomp_set_mode_filter(unsigned int flags, 757 const char __user *filter) 758 { 759 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 760 struct seccomp_filter *prepared = NULL; 761 long ret = -EINVAL; 762 763 /* Validate flags. */ 764 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 765 return -EINVAL; 766 767 /* Prepare the new filter before holding any locks. */ 768 prepared = seccomp_prepare_user_filter(filter); 769 if (IS_ERR(prepared)) 770 return PTR_ERR(prepared); 771 772 /* 773 * Make sure we cannot change seccomp or nnp state via TSYNC 774 * while another thread is in the middle of calling exec. 775 */ 776 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 777 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 778 goto out_free; 779 780 spin_lock_irq(¤t->sighand->siglock); 781 782 if (!seccomp_may_assign_mode(seccomp_mode)) 783 goto out; 784 785 ret = seccomp_attach_filter(flags, prepared); 786 if (ret) 787 goto out; 788 /* Do not free the successfully attached filter. */ 789 prepared = NULL; 790 791 seccomp_assign_mode(current, seccomp_mode); 792 out: 793 spin_unlock_irq(¤t->sighand->siglock); 794 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 795 mutex_unlock(¤t->signal->cred_guard_mutex); 796 out_free: 797 seccomp_filter_free(prepared); 798 return ret; 799 } 800 #else 801 static inline long seccomp_set_mode_filter(unsigned int flags, 802 const char __user *filter) 803 { 804 return -EINVAL; 805 } 806 #endif 807 808 /* Common entry point for both prctl and syscall. */ 809 static long do_seccomp(unsigned int op, unsigned int flags, 810 const char __user *uargs) 811 { 812 switch (op) { 813 case SECCOMP_SET_MODE_STRICT: 814 if (flags != 0 || uargs != NULL) 815 return -EINVAL; 816 return seccomp_set_mode_strict(); 817 case SECCOMP_SET_MODE_FILTER: 818 return seccomp_set_mode_filter(flags, uargs); 819 default: 820 return -EINVAL; 821 } 822 } 823 824 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 825 const char __user *, uargs) 826 { 827 return do_seccomp(op, flags, uargs); 828 } 829 830 /** 831 * prctl_set_seccomp: configures current->seccomp.mode 832 * @seccomp_mode: requested mode to use 833 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 834 * 835 * Returns 0 on success or -EINVAL on failure. 836 */ 837 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 838 { 839 unsigned int op; 840 char __user *uargs; 841 842 switch (seccomp_mode) { 843 case SECCOMP_MODE_STRICT: 844 op = SECCOMP_SET_MODE_STRICT; 845 /* 846 * Setting strict mode through prctl always ignored filter, 847 * so make sure it is always NULL here to pass the internal 848 * check in do_seccomp(). 849 */ 850 uargs = NULL; 851 break; 852 case SECCOMP_MODE_FILTER: 853 op = SECCOMP_SET_MODE_FILTER; 854 uargs = filter; 855 break; 856 default: 857 return -EINVAL; 858 } 859 860 /* prctl interface doesn't have flags, so they are always zero. */ 861 return do_seccomp(op, 0, uargs); 862 } 863