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 * @prog: the BPF program to evaluate 45 * 46 * seccomp_filter objects are organized in a tree linked via the @prev 47 * pointer. For any task, it appears to be a singly-linked list starting 48 * with current->seccomp.filter, the most recently attached or inherited filter. 49 * However, multiple filters may share a @prev node, by way of fork(), which 50 * results in a unidirectional tree existing in memory. This is similar to 51 * how namespaces work. 52 * 53 * seccomp_filter objects should never be modified after being attached 54 * to a task_struct (other than @usage). 55 */ 56 struct seccomp_filter { 57 atomic_t usage; 58 struct seccomp_filter *prev; 59 struct bpf_prog *prog; 60 }; 61 62 /* Limit any path through the tree to 256KB worth of instructions. */ 63 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter)) 64 65 /* 66 * Endianness is explicitly ignored and left for BPF program authors to manage 67 * as per the specific architecture. 68 */ 69 static void populate_seccomp_data(struct seccomp_data *sd) 70 { 71 struct task_struct *task = current; 72 struct pt_regs *regs = task_pt_regs(task); 73 unsigned long args[6]; 74 75 sd->nr = syscall_get_nr(task, regs); 76 sd->arch = syscall_get_arch(); 77 syscall_get_arguments(task, regs, 0, 6, args); 78 sd->args[0] = args[0]; 79 sd->args[1] = args[1]; 80 sd->args[2] = args[2]; 81 sd->args[3] = args[3]; 82 sd->args[4] = args[4]; 83 sd->args[5] = args[5]; 84 sd->instruction_pointer = KSTK_EIP(task); 85 } 86 87 /** 88 * seccomp_check_filter - verify seccomp filter code 89 * @filter: filter to verify 90 * @flen: length of filter 91 * 92 * Takes a previously checked filter (by bpf_check_classic) and 93 * redirects all filter code that loads struct sk_buff data 94 * and related data through seccomp_bpf_load. It also 95 * enforces length and alignment checking of those loads. 96 * 97 * Returns 0 if the rule set is legal or -EINVAL if not. 98 */ 99 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) 100 { 101 int pc; 102 for (pc = 0; pc < flen; pc++) { 103 struct sock_filter *ftest = &filter[pc]; 104 u16 code = ftest->code; 105 u32 k = ftest->k; 106 107 switch (code) { 108 case BPF_LD | BPF_W | BPF_ABS: 109 ftest->code = BPF_LDX | BPF_W | BPF_ABS; 110 /* 32-bit aligned and not out of bounds. */ 111 if (k >= sizeof(struct seccomp_data) || k & 3) 112 return -EINVAL; 113 continue; 114 case BPF_LD | BPF_W | BPF_LEN: 115 ftest->code = BPF_LD | BPF_IMM; 116 ftest->k = sizeof(struct seccomp_data); 117 continue; 118 case BPF_LDX | BPF_W | BPF_LEN: 119 ftest->code = BPF_LDX | BPF_IMM; 120 ftest->k = sizeof(struct seccomp_data); 121 continue; 122 /* Explicitly include allowed calls. */ 123 case BPF_RET | BPF_K: 124 case BPF_RET | BPF_A: 125 case BPF_ALU | BPF_ADD | BPF_K: 126 case BPF_ALU | BPF_ADD | BPF_X: 127 case BPF_ALU | BPF_SUB | BPF_K: 128 case BPF_ALU | BPF_SUB | BPF_X: 129 case BPF_ALU | BPF_MUL | BPF_K: 130 case BPF_ALU | BPF_MUL | BPF_X: 131 case BPF_ALU | BPF_DIV | BPF_K: 132 case BPF_ALU | BPF_DIV | BPF_X: 133 case BPF_ALU | BPF_AND | BPF_K: 134 case BPF_ALU | BPF_AND | BPF_X: 135 case BPF_ALU | BPF_OR | BPF_K: 136 case BPF_ALU | BPF_OR | BPF_X: 137 case BPF_ALU | BPF_XOR | BPF_K: 138 case BPF_ALU | BPF_XOR | BPF_X: 139 case BPF_ALU | BPF_LSH | BPF_K: 140 case BPF_ALU | BPF_LSH | BPF_X: 141 case BPF_ALU | BPF_RSH | BPF_K: 142 case BPF_ALU | BPF_RSH | BPF_X: 143 case BPF_ALU | BPF_NEG: 144 case BPF_LD | BPF_IMM: 145 case BPF_LDX | BPF_IMM: 146 case BPF_MISC | BPF_TAX: 147 case BPF_MISC | BPF_TXA: 148 case BPF_LD | BPF_MEM: 149 case BPF_LDX | BPF_MEM: 150 case BPF_ST: 151 case BPF_STX: 152 case BPF_JMP | BPF_JA: 153 case BPF_JMP | BPF_JEQ | BPF_K: 154 case BPF_JMP | BPF_JEQ | BPF_X: 155 case BPF_JMP | BPF_JGE | BPF_K: 156 case BPF_JMP | BPF_JGE | BPF_X: 157 case BPF_JMP | BPF_JGT | BPF_K: 158 case BPF_JMP | BPF_JGT | BPF_X: 159 case BPF_JMP | BPF_JSET | BPF_K: 160 case BPF_JMP | BPF_JSET | BPF_X: 161 continue; 162 default: 163 return -EINVAL; 164 } 165 } 166 return 0; 167 } 168 169 /** 170 * seccomp_run_filters - evaluates all seccomp filters against @sd 171 * @sd: optional seccomp data to be passed to filters 172 * 173 * Returns valid seccomp BPF response codes. 174 */ 175 static u32 seccomp_run_filters(const struct seccomp_data *sd) 176 { 177 struct seccomp_data sd_local; 178 u32 ret = SECCOMP_RET_ALLOW; 179 /* Make sure cross-thread synced filter points somewhere sane. */ 180 struct seccomp_filter *f = 181 lockless_dereference(current->seccomp.filter); 182 183 /* Ensure unexpected behavior doesn't result in failing open. */ 184 if (unlikely(WARN_ON(f == NULL))) 185 return SECCOMP_RET_KILL; 186 187 if (!sd) { 188 populate_seccomp_data(&sd_local); 189 sd = &sd_local; 190 } 191 192 /* 193 * All filters in the list are evaluated and the lowest BPF return 194 * value always takes priority (ignoring the DATA). 195 */ 196 for (; f; f = f->prev) { 197 u32 cur_ret = BPF_PROG_RUN(f->prog, sd); 198 199 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION)) 200 ret = cur_ret; 201 } 202 return ret; 203 } 204 #endif /* CONFIG_SECCOMP_FILTER */ 205 206 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 207 { 208 assert_spin_locked(¤t->sighand->siglock); 209 210 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) 211 return false; 212 213 return true; 214 } 215 216 static inline void seccomp_assign_mode(struct task_struct *task, 217 unsigned long seccomp_mode) 218 { 219 assert_spin_locked(&task->sighand->siglock); 220 221 task->seccomp.mode = seccomp_mode; 222 /* 223 * Make sure TIF_SECCOMP cannot be set before the mode (and 224 * filter) is set. 225 */ 226 smp_mb__before_atomic(); 227 set_tsk_thread_flag(task, TIF_SECCOMP); 228 } 229 230 #ifdef CONFIG_SECCOMP_FILTER 231 /* Returns 1 if the parent is an ancestor of the child. */ 232 static int is_ancestor(struct seccomp_filter *parent, 233 struct seccomp_filter *child) 234 { 235 /* NULL is the root ancestor. */ 236 if (parent == NULL) 237 return 1; 238 for (; child; child = child->prev) 239 if (child == parent) 240 return 1; 241 return 0; 242 } 243 244 /** 245 * seccomp_can_sync_threads: checks if all threads can be synchronized 246 * 247 * Expects sighand and cred_guard_mutex locks to be held. 248 * 249 * Returns 0 on success, -ve on error, or the pid of a thread which was 250 * either not in the correct seccomp mode or it did not have an ancestral 251 * seccomp filter. 252 */ 253 static inline pid_t seccomp_can_sync_threads(void) 254 { 255 struct task_struct *thread, *caller; 256 257 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 258 assert_spin_locked(¤t->sighand->siglock); 259 260 /* Validate all threads being eligible for synchronization. */ 261 caller = current; 262 for_each_thread(caller, thread) { 263 pid_t failed; 264 265 /* Skip current, since it is initiating the sync. */ 266 if (thread == caller) 267 continue; 268 269 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || 270 (thread->seccomp.mode == SECCOMP_MODE_FILTER && 271 is_ancestor(thread->seccomp.filter, 272 caller->seccomp.filter))) 273 continue; 274 275 /* Return the first thread that cannot be synchronized. */ 276 failed = task_pid_vnr(thread); 277 /* If the pid cannot be resolved, then return -ESRCH */ 278 if (unlikely(WARN_ON(failed == 0))) 279 failed = -ESRCH; 280 return failed; 281 } 282 283 return 0; 284 } 285 286 /** 287 * seccomp_sync_threads: sets all threads to use current's filter 288 * 289 * Expects sighand and cred_guard_mutex locks to be held, and for 290 * seccomp_can_sync_threads() to have returned success already 291 * without dropping the locks. 292 * 293 */ 294 static inline void seccomp_sync_threads(void) 295 { 296 struct task_struct *thread, *caller; 297 298 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 299 assert_spin_locked(¤t->sighand->siglock); 300 301 /* Synchronize all threads. */ 302 caller = current; 303 for_each_thread(caller, thread) { 304 /* Skip current, since it needs no changes. */ 305 if (thread == caller) 306 continue; 307 308 /* Get a task reference for the new leaf node. */ 309 get_seccomp_filter(caller); 310 /* 311 * Drop the task reference to the shared ancestor since 312 * current's path will hold a reference. (This also 313 * allows a put before the assignment.) 314 */ 315 put_seccomp_filter(thread); 316 smp_store_release(&thread->seccomp.filter, 317 caller->seccomp.filter); 318 319 /* 320 * Don't let an unprivileged task work around 321 * the no_new_privs restriction by creating 322 * a thread that sets it up, enters seccomp, 323 * then dies. 324 */ 325 if (task_no_new_privs(caller)) 326 task_set_no_new_privs(thread); 327 328 /* 329 * Opt the other thread into seccomp if needed. 330 * As threads are considered to be trust-realm 331 * equivalent (see ptrace_may_access), it is safe to 332 * allow one thread to transition the other. 333 */ 334 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) 335 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 336 } 337 } 338 339 /** 340 * seccomp_prepare_filter: Prepares a seccomp filter for use. 341 * @fprog: BPF program to install 342 * 343 * Returns filter on success or an ERR_PTR on failure. 344 */ 345 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 346 { 347 struct seccomp_filter *sfilter; 348 int ret; 349 const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE); 350 351 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 352 return ERR_PTR(-EINVAL); 353 354 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 355 356 /* 357 * Installing a seccomp filter requires that the task has 358 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 359 * This avoids scenarios where unprivileged tasks can affect the 360 * behavior of privileged children. 361 */ 362 if (!task_no_new_privs(current) && 363 security_capable_noaudit(current_cred(), current_user_ns(), 364 CAP_SYS_ADMIN) != 0) 365 return ERR_PTR(-EACCES); 366 367 /* Allocate a new seccomp_filter */ 368 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); 369 if (!sfilter) 370 return ERR_PTR(-ENOMEM); 371 372 ret = bpf_prog_create_from_user(&sfilter->prog, fprog, 373 seccomp_check_filter, save_orig); 374 if (ret < 0) { 375 kfree(sfilter); 376 return ERR_PTR(ret); 377 } 378 379 atomic_set(&sfilter->usage, 1); 380 381 return sfilter; 382 } 383 384 /** 385 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 386 * @user_filter: pointer to the user data containing a sock_fprog. 387 * 388 * Returns 0 on success and non-zero otherwise. 389 */ 390 static struct seccomp_filter * 391 seccomp_prepare_user_filter(const char __user *user_filter) 392 { 393 struct sock_fprog fprog; 394 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 395 396 #ifdef CONFIG_COMPAT 397 if (in_compat_syscall()) { 398 struct compat_sock_fprog fprog32; 399 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 400 goto out; 401 fprog.len = fprog32.len; 402 fprog.filter = compat_ptr(fprog32.filter); 403 } else /* falls through to the if below. */ 404 #endif 405 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 406 goto out; 407 filter = seccomp_prepare_filter(&fprog); 408 out: 409 return filter; 410 } 411 412 /** 413 * seccomp_attach_filter: validate and attach filter 414 * @flags: flags to change filter behavior 415 * @filter: seccomp filter to add to the current process 416 * 417 * Caller must be holding current->sighand->siglock lock. 418 * 419 * Returns 0 on success, -ve on error. 420 */ 421 static long seccomp_attach_filter(unsigned int flags, 422 struct seccomp_filter *filter) 423 { 424 unsigned long total_insns; 425 struct seccomp_filter *walker; 426 427 assert_spin_locked(¤t->sighand->siglock); 428 429 /* Validate resulting filter length. */ 430 total_insns = filter->prog->len; 431 for (walker = current->seccomp.filter; walker; walker = walker->prev) 432 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 433 if (total_insns > MAX_INSNS_PER_PATH) 434 return -ENOMEM; 435 436 /* If thread sync has been requested, check that it is possible. */ 437 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 438 int ret; 439 440 ret = seccomp_can_sync_threads(); 441 if (ret) 442 return ret; 443 } 444 445 /* 446 * If there is an existing filter, make it the prev and don't drop its 447 * task reference. 448 */ 449 filter->prev = current->seccomp.filter; 450 current->seccomp.filter = filter; 451 452 /* Now that the new filter is in place, synchronize to all threads. */ 453 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 454 seccomp_sync_threads(); 455 456 return 0; 457 } 458 459 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 460 void get_seccomp_filter(struct task_struct *tsk) 461 { 462 struct seccomp_filter *orig = tsk->seccomp.filter; 463 if (!orig) 464 return; 465 /* Reference count is bounded by the number of total processes. */ 466 atomic_inc(&orig->usage); 467 } 468 469 static inline void seccomp_filter_free(struct seccomp_filter *filter) 470 { 471 if (filter) { 472 bpf_prog_destroy(filter->prog); 473 kfree(filter); 474 } 475 } 476 477 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 478 void put_seccomp_filter(struct task_struct *tsk) 479 { 480 struct seccomp_filter *orig = tsk->seccomp.filter; 481 /* Clean up single-reference branches iteratively. */ 482 while (orig && atomic_dec_and_test(&orig->usage)) { 483 struct seccomp_filter *freeme = orig; 484 orig = orig->prev; 485 seccomp_filter_free(freeme); 486 } 487 } 488 489 /** 490 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 491 * @syscall: syscall number to send to userland 492 * @reason: filter-supplied reason code to send to userland (via si_errno) 493 * 494 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 495 */ 496 static void seccomp_send_sigsys(int syscall, int reason) 497 { 498 struct siginfo info; 499 memset(&info, 0, sizeof(info)); 500 info.si_signo = SIGSYS; 501 info.si_code = SYS_SECCOMP; 502 info.si_call_addr = (void __user *)KSTK_EIP(current); 503 info.si_errno = reason; 504 info.si_arch = syscall_get_arch(); 505 info.si_syscall = syscall; 506 force_sig_info(SIGSYS, &info, current); 507 } 508 #endif /* CONFIG_SECCOMP_FILTER */ 509 510 /* 511 * Secure computing mode 1 allows only read/write/exit/sigreturn. 512 * To be fully secure this must be combined with rlimit 513 * to limit the stack allocations too. 514 */ 515 static const int mode1_syscalls[] = { 516 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 517 0, /* null terminated */ 518 }; 519 520 static void __secure_computing_strict(int this_syscall) 521 { 522 const int *syscall_whitelist = mode1_syscalls; 523 #ifdef CONFIG_COMPAT 524 if (in_compat_syscall()) 525 syscall_whitelist = get_compat_mode1_syscalls(); 526 #endif 527 do { 528 if (*syscall_whitelist == this_syscall) 529 return; 530 } while (*++syscall_whitelist); 531 532 #ifdef SECCOMP_DEBUG 533 dump_stack(); 534 #endif 535 audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL); 536 do_exit(SIGKILL); 537 } 538 539 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 540 void secure_computing_strict(int this_syscall) 541 { 542 int mode = current->seccomp.mode; 543 544 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 545 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 546 return; 547 548 if (mode == SECCOMP_MODE_DISABLED) 549 return; 550 else if (mode == SECCOMP_MODE_STRICT) 551 __secure_computing_strict(this_syscall); 552 else 553 BUG(); 554 } 555 #else 556 557 #ifdef CONFIG_SECCOMP_FILTER 558 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 559 const bool recheck_after_trace) 560 { 561 u32 filter_ret, action; 562 int data; 563 564 /* 565 * Make sure that any changes to mode from another thread have 566 * been seen after TIF_SECCOMP was seen. 567 */ 568 rmb(); 569 570 filter_ret = seccomp_run_filters(sd); 571 data = filter_ret & SECCOMP_RET_DATA; 572 action = filter_ret & SECCOMP_RET_ACTION; 573 574 switch (action) { 575 case SECCOMP_RET_ERRNO: 576 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 577 if (data > MAX_ERRNO) 578 data = MAX_ERRNO; 579 syscall_set_return_value(current, task_pt_regs(current), 580 -data, 0); 581 goto skip; 582 583 case SECCOMP_RET_TRAP: 584 /* Show the handler the original registers. */ 585 syscall_rollback(current, task_pt_regs(current)); 586 /* Let the filter pass back 16 bits of data. */ 587 seccomp_send_sigsys(this_syscall, data); 588 goto skip; 589 590 case SECCOMP_RET_TRACE: 591 /* We've been put in this state by the ptracer already. */ 592 if (recheck_after_trace) 593 return 0; 594 595 /* ENOSYS these calls if there is no tracer attached. */ 596 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 597 syscall_set_return_value(current, 598 task_pt_regs(current), 599 -ENOSYS, 0); 600 goto skip; 601 } 602 603 /* Allow the BPF to provide the event message */ 604 ptrace_event(PTRACE_EVENT_SECCOMP, data); 605 /* 606 * The delivery of a fatal signal during event 607 * notification may silently skip tracer notification, 608 * which could leave us with a potentially unmodified 609 * syscall that the tracer would have liked to have 610 * changed. Since the process is about to die, we just 611 * force the syscall to be skipped and let the signal 612 * kill the process and correctly handle any tracer exit 613 * notifications. 614 */ 615 if (fatal_signal_pending(current)) 616 goto skip; 617 /* Check if the tracer forced the syscall to be skipped. */ 618 this_syscall = syscall_get_nr(current, task_pt_regs(current)); 619 if (this_syscall < 0) 620 goto skip; 621 622 /* 623 * Recheck the syscall, since it may have changed. This 624 * intentionally uses a NULL struct seccomp_data to force 625 * a reload of all registers. This does not goto skip since 626 * a skip would have already been reported. 627 */ 628 if (__seccomp_filter(this_syscall, NULL, true)) 629 return -1; 630 631 return 0; 632 633 case SECCOMP_RET_ALLOW: 634 return 0; 635 636 case SECCOMP_RET_KILL: 637 default: 638 audit_seccomp(this_syscall, SIGSYS, action); 639 do_exit(SIGSYS); 640 } 641 642 unreachable(); 643 644 skip: 645 audit_seccomp(this_syscall, 0, action); 646 return -1; 647 } 648 #else 649 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, 650 const bool recheck_after_trace) 651 { 652 BUG(); 653 } 654 #endif 655 656 int __secure_computing(const struct seccomp_data *sd) 657 { 658 int mode = current->seccomp.mode; 659 int this_syscall; 660 661 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && 662 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 663 return 0; 664 665 this_syscall = sd ? sd->nr : 666 syscall_get_nr(current, task_pt_regs(current)); 667 668 switch (mode) { 669 case SECCOMP_MODE_STRICT: 670 __secure_computing_strict(this_syscall); /* may call do_exit */ 671 return 0; 672 case SECCOMP_MODE_FILTER: 673 return __seccomp_filter(this_syscall, sd, false); 674 default: 675 BUG(); 676 } 677 } 678 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 679 680 long prctl_get_seccomp(void) 681 { 682 return current->seccomp.mode; 683 } 684 685 /** 686 * seccomp_set_mode_strict: internal function for setting strict seccomp 687 * 688 * Once current->seccomp.mode is non-zero, it may not be changed. 689 * 690 * Returns 0 on success or -EINVAL on failure. 691 */ 692 static long seccomp_set_mode_strict(void) 693 { 694 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 695 long ret = -EINVAL; 696 697 spin_lock_irq(¤t->sighand->siglock); 698 699 if (!seccomp_may_assign_mode(seccomp_mode)) 700 goto out; 701 702 #ifdef TIF_NOTSC 703 disable_TSC(); 704 #endif 705 seccomp_assign_mode(current, seccomp_mode); 706 ret = 0; 707 708 out: 709 spin_unlock_irq(¤t->sighand->siglock); 710 711 return ret; 712 } 713 714 #ifdef CONFIG_SECCOMP_FILTER 715 /** 716 * seccomp_set_mode_filter: internal function for setting seccomp filter 717 * @flags: flags to change filter behavior 718 * @filter: struct sock_fprog containing filter 719 * 720 * This function may be called repeatedly to install additional filters. 721 * Every filter successfully installed will be evaluated (in reverse order) 722 * for each system call the task makes. 723 * 724 * Once current->seccomp.mode is non-zero, it may not be changed. 725 * 726 * Returns 0 on success or -EINVAL on failure. 727 */ 728 static long seccomp_set_mode_filter(unsigned int flags, 729 const char __user *filter) 730 { 731 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 732 struct seccomp_filter *prepared = NULL; 733 long ret = -EINVAL; 734 735 /* Validate flags. */ 736 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 737 return -EINVAL; 738 739 /* Prepare the new filter before holding any locks. */ 740 prepared = seccomp_prepare_user_filter(filter); 741 if (IS_ERR(prepared)) 742 return PTR_ERR(prepared); 743 744 /* 745 * Make sure we cannot change seccomp or nnp state via TSYNC 746 * while another thread is in the middle of calling exec. 747 */ 748 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 749 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 750 goto out_free; 751 752 spin_lock_irq(¤t->sighand->siglock); 753 754 if (!seccomp_may_assign_mode(seccomp_mode)) 755 goto out; 756 757 ret = seccomp_attach_filter(flags, prepared); 758 if (ret) 759 goto out; 760 /* Do not free the successfully attached filter. */ 761 prepared = NULL; 762 763 seccomp_assign_mode(current, seccomp_mode); 764 out: 765 spin_unlock_irq(¤t->sighand->siglock); 766 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 767 mutex_unlock(¤t->signal->cred_guard_mutex); 768 out_free: 769 seccomp_filter_free(prepared); 770 return ret; 771 } 772 #else 773 static inline long seccomp_set_mode_filter(unsigned int flags, 774 const char __user *filter) 775 { 776 return -EINVAL; 777 } 778 #endif 779 780 /* Common entry point for both prctl and syscall. */ 781 static long do_seccomp(unsigned int op, unsigned int flags, 782 const char __user *uargs) 783 { 784 switch (op) { 785 case SECCOMP_SET_MODE_STRICT: 786 if (flags != 0 || uargs != NULL) 787 return -EINVAL; 788 return seccomp_set_mode_strict(); 789 case SECCOMP_SET_MODE_FILTER: 790 return seccomp_set_mode_filter(flags, uargs); 791 default: 792 return -EINVAL; 793 } 794 } 795 796 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 797 const char __user *, uargs) 798 { 799 return do_seccomp(op, flags, uargs); 800 } 801 802 /** 803 * prctl_set_seccomp: configures current->seccomp.mode 804 * @seccomp_mode: requested mode to use 805 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 806 * 807 * Returns 0 on success or -EINVAL on failure. 808 */ 809 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 810 { 811 unsigned int op; 812 char __user *uargs; 813 814 switch (seccomp_mode) { 815 case SECCOMP_MODE_STRICT: 816 op = SECCOMP_SET_MODE_STRICT; 817 /* 818 * Setting strict mode through prctl always ignored filter, 819 * so make sure it is always NULL here to pass the internal 820 * check in do_seccomp(). 821 */ 822 uargs = NULL; 823 break; 824 case SECCOMP_MODE_FILTER: 825 op = SECCOMP_SET_MODE_FILTER; 826 uargs = filter; 827 break; 828 default: 829 return -EINVAL; 830 } 831 832 /* prctl interface doesn't have flags, so they are always zero. */ 833 return do_seccomp(op, 0, uargs); 834 } 835 836 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) 837 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, 838 void __user *data) 839 { 840 struct seccomp_filter *filter; 841 struct sock_fprog_kern *fprog; 842 long ret; 843 unsigned long count = 0; 844 845 if (!capable(CAP_SYS_ADMIN) || 846 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 847 return -EACCES; 848 } 849 850 spin_lock_irq(&task->sighand->siglock); 851 if (task->seccomp.mode != SECCOMP_MODE_FILTER) { 852 ret = -EINVAL; 853 goto out; 854 } 855 856 filter = task->seccomp.filter; 857 while (filter) { 858 filter = filter->prev; 859 count++; 860 } 861 862 if (filter_off >= count) { 863 ret = -ENOENT; 864 goto out; 865 } 866 count -= filter_off; 867 868 filter = task->seccomp.filter; 869 while (filter && count > 1) { 870 filter = filter->prev; 871 count--; 872 } 873 874 if (WARN_ON(count != 1 || !filter)) { 875 /* The filter tree shouldn't shrink while we're using it. */ 876 ret = -ENOENT; 877 goto out; 878 } 879 880 fprog = filter->prog->orig_prog; 881 if (!fprog) { 882 /* This must be a new non-cBPF filter, since we save 883 * every cBPF filter's orig_prog above when 884 * CONFIG_CHECKPOINT_RESTORE is enabled. 885 */ 886 ret = -EMEDIUMTYPE; 887 goto out; 888 } 889 890 ret = fprog->len; 891 if (!data) 892 goto out; 893 894 get_seccomp_filter(task); 895 spin_unlock_irq(&task->sighand->siglock); 896 897 if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) 898 ret = -EFAULT; 899 900 put_seccomp_filter(task); 901 return ret; 902 903 out: 904 spin_unlock_irq(&task->sighand->siglock); 905 return ret; 906 } 907 #endif 908