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 */ 57struct 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 */ 70static 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 */ 100static 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 */ 176static 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 208static 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 218static 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. */ 234static 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 */ 255static 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 */ 296static 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 /* 322 * Don't let an unprivileged task work around 323 * the no_new_privs restriction by creating 324 * a thread that sets it up, enters seccomp, 325 * then dies. 326 */ 327 if (task_no_new_privs(caller)) 328 task_set_no_new_privs(thread); 329 330 /* 331 * Opt the other thread into seccomp if needed. 332 * As threads are considered to be trust-realm 333 * equivalent (see ptrace_may_access), it is safe to 334 * allow one thread to transition the other. 335 */ 336 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) 337 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 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 */ 347static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 348{ 349 struct seccomp_filter *filter; 350 unsigned long fp_size; 351 struct sock_filter *fp; 352 int new_len; 353 long ret; 354 355 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 356 return ERR_PTR(-EINVAL); 357 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 358 fp_size = fprog->len * sizeof(struct sock_filter); 359 360 /* 361 * Installing a seccomp filter requires that the task has 362 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 363 * This avoids scenarios where unprivileged tasks can affect the 364 * behavior of privileged children. 365 */ 366 if (!task_no_new_privs(current) && 367 security_capable_noaudit(current_cred(), current_user_ns(), 368 CAP_SYS_ADMIN) != 0) 369 return ERR_PTR(-EACCES); 370 371 fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN); 372 if (!fp) 373 return ERR_PTR(-ENOMEM); 374 375 /* Copy the instructions from fprog. */ 376 ret = -EFAULT; 377 if (copy_from_user(fp, fprog->filter, fp_size)) 378 goto free_prog; 379 380 /* Check and rewrite the fprog via the skb checker */ 381 ret = bpf_check_classic(fp, fprog->len); 382 if (ret) 383 goto free_prog; 384 385 /* Check and rewrite the fprog for seccomp use */ 386 ret = seccomp_check_filter(fp, fprog->len); 387 if (ret) 388 goto free_prog; 389 390 /* Convert 'sock_filter' insns to 'bpf_insn' insns */ 391 ret = bpf_convert_filter(fp, fprog->len, NULL, &new_len); 392 if (ret) 393 goto free_prog; 394 395 /* Allocate a new seccomp_filter */ 396 ret = -ENOMEM; 397 filter = kzalloc(sizeof(struct seccomp_filter), 398 GFP_KERNEL|__GFP_NOWARN); 399 if (!filter) 400 goto free_prog; 401 402 filter->prog = bpf_prog_alloc(bpf_prog_size(new_len), __GFP_NOWARN); 403 if (!filter->prog) 404 goto free_filter; 405 406 ret = bpf_convert_filter(fp, fprog->len, filter->prog->insnsi, &new_len); 407 if (ret) 408 goto free_filter_prog; 409 410 kfree(fp); 411 atomic_set(&filter->usage, 1); 412 filter->prog->len = new_len; 413 414 bpf_prog_select_runtime(filter->prog); 415 416 return filter; 417 418free_filter_prog: 419 __bpf_prog_free(filter->prog); 420free_filter: 421 kfree(filter); 422free_prog: 423 kfree(fp); 424 return ERR_PTR(ret); 425} 426 427/** 428 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 429 * @user_filter: pointer to the user data containing a sock_fprog. 430 * 431 * Returns 0 on success and non-zero otherwise. 432 */ 433static struct seccomp_filter * 434seccomp_prepare_user_filter(const char __user *user_filter) 435{ 436 struct sock_fprog fprog; 437 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 438 439#ifdef CONFIG_COMPAT 440 if (is_compat_task()) { 441 struct compat_sock_fprog fprog32; 442 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 443 goto out; 444 fprog.len = fprog32.len; 445 fprog.filter = compat_ptr(fprog32.filter); 446 } else /* falls through to the if below. */ 447#endif 448 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 449 goto out; 450 filter = seccomp_prepare_filter(&fprog); 451out: 452 return filter; 453} 454 455/** 456 * seccomp_attach_filter: validate and attach filter 457 * @flags: flags to change filter behavior 458 * @filter: seccomp filter to add to the current process 459 * 460 * Caller must be holding current->sighand->siglock lock. 461 * 462 * Returns 0 on success, -ve on error. 463 */ 464static long seccomp_attach_filter(unsigned int flags, 465 struct seccomp_filter *filter) 466{ 467 unsigned long total_insns; 468 struct seccomp_filter *walker; 469 470 assert_spin_locked(¤t->sighand->siglock); 471 472 /* Validate resulting filter length. */ 473 total_insns = filter->prog->len; 474 for (walker = current->seccomp.filter; walker; walker = walker->prev) 475 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 476 if (total_insns > MAX_INSNS_PER_PATH) 477 return -ENOMEM; 478 479 /* If thread sync has been requested, check that it is possible. */ 480 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 481 int ret; 482 483 ret = seccomp_can_sync_threads(); 484 if (ret) 485 return ret; 486 } 487 488 /* 489 * If there is an existing filter, make it the prev and don't drop its 490 * task reference. 491 */ 492 filter->prev = current->seccomp.filter; 493 current->seccomp.filter = filter; 494 495 /* Now that the new filter is in place, synchronize to all threads. */ 496 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 497 seccomp_sync_threads(); 498 499 return 0; 500} 501 502/* get_seccomp_filter - increments the reference count of the filter on @tsk */ 503void get_seccomp_filter(struct task_struct *tsk) 504{ 505 struct seccomp_filter *orig = tsk->seccomp.filter; 506 if (!orig) 507 return; 508 /* Reference count is bounded by the number of total processes. */ 509 atomic_inc(&orig->usage); 510} 511 512static inline void seccomp_filter_free(struct seccomp_filter *filter) 513{ 514 if (filter) { 515 bpf_prog_free(filter->prog); 516 kfree(filter); 517 } 518} 519 520/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 521void put_seccomp_filter(struct task_struct *tsk) 522{ 523 struct seccomp_filter *orig = tsk->seccomp.filter; 524 /* Clean up single-reference branches iteratively. */ 525 while (orig && atomic_dec_and_test(&orig->usage)) { 526 struct seccomp_filter *freeme = orig; 527 orig = orig->prev; 528 seccomp_filter_free(freeme); 529 } 530} 531 532/** 533 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 534 * @syscall: syscall number to send to userland 535 * @reason: filter-supplied reason code to send to userland (via si_errno) 536 * 537 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 538 */ 539static void seccomp_send_sigsys(int syscall, int reason) 540{ 541 struct siginfo info; 542 memset(&info, 0, sizeof(info)); 543 info.si_signo = SIGSYS; 544 info.si_code = SYS_SECCOMP; 545 info.si_call_addr = (void __user *)KSTK_EIP(current); 546 info.si_errno = reason; 547 info.si_arch = syscall_get_arch(); 548 info.si_syscall = syscall; 549 force_sig_info(SIGSYS, &info, current); 550} 551#endif /* CONFIG_SECCOMP_FILTER */ 552 553/* 554 * Secure computing mode 1 allows only read/write/exit/sigreturn. 555 * To be fully secure this must be combined with rlimit 556 * to limit the stack allocations too. 557 */ 558static int mode1_syscalls[] = { 559 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 560 0, /* null terminated */ 561}; 562 563#ifdef CONFIG_COMPAT 564static int mode1_syscalls_32[] = { 565 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32, 566 0, /* null terminated */ 567}; 568#endif 569 570static void __secure_computing_strict(int this_syscall) 571{ 572 int *syscall_whitelist = mode1_syscalls; 573#ifdef CONFIG_COMPAT 574 if (is_compat_task()) 575 syscall_whitelist = mode1_syscalls_32; 576#endif 577 do { 578 if (*syscall_whitelist == this_syscall) 579 return; 580 } while (*++syscall_whitelist); 581 582#ifdef SECCOMP_DEBUG 583 dump_stack(); 584#endif 585 audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL); 586 do_exit(SIGKILL); 587} 588 589#ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 590void secure_computing_strict(int this_syscall) 591{ 592 int mode = current->seccomp.mode; 593 594 if (mode == 0) 595 return; 596 else if (mode == SECCOMP_MODE_STRICT) 597 __secure_computing_strict(this_syscall); 598 else 599 BUG(); 600} 601#else 602int __secure_computing(void) 603{ 604 u32 phase1_result = seccomp_phase1(NULL); 605 606 if (likely(phase1_result == SECCOMP_PHASE1_OK)) 607 return 0; 608 else if (likely(phase1_result == SECCOMP_PHASE1_SKIP)) 609 return -1; 610 else 611 return seccomp_phase2(phase1_result); 612} 613 614#ifdef CONFIG_SECCOMP_FILTER 615static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd) 616{ 617 u32 filter_ret, action; 618 int data; 619 620 /* 621 * Make sure that any changes to mode from another thread have 622 * been seen after TIF_SECCOMP was seen. 623 */ 624 rmb(); 625 626 filter_ret = seccomp_run_filters(sd); 627 data = filter_ret & SECCOMP_RET_DATA; 628 action = filter_ret & SECCOMP_RET_ACTION; 629 630 switch (action) { 631 case SECCOMP_RET_ERRNO: 632 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 633 if (data > MAX_ERRNO) 634 data = MAX_ERRNO; 635 syscall_set_return_value(current, task_pt_regs(current), 636 -data, 0); 637 goto skip; 638 639 case SECCOMP_RET_TRAP: 640 /* Show the handler the original registers. */ 641 syscall_rollback(current, task_pt_regs(current)); 642 /* Let the filter pass back 16 bits of data. */ 643 seccomp_send_sigsys(this_syscall, data); 644 goto skip; 645 646 case SECCOMP_RET_TRACE: 647 return filter_ret; /* Save the rest for phase 2. */ 648 649 case SECCOMP_RET_ALLOW: 650 return SECCOMP_PHASE1_OK; 651 652 case SECCOMP_RET_KILL: 653 default: 654 audit_seccomp(this_syscall, SIGSYS, action); 655 do_exit(SIGSYS); 656 } 657 658 unreachable(); 659 660skip: 661 audit_seccomp(this_syscall, 0, action); 662 return SECCOMP_PHASE1_SKIP; 663} 664#endif 665 666/** 667 * seccomp_phase1() - run fast path seccomp checks on the current syscall 668 * @arg sd: The seccomp_data or NULL 669 * 670 * This only reads pt_regs via the syscall_xyz helpers. The only change 671 * it will make to pt_regs is via syscall_set_return_value, and it will 672 * only do that if it returns SECCOMP_PHASE1_SKIP. 673 * 674 * If sd is provided, it will not read pt_regs at all. 675 * 676 * It may also call do_exit or force a signal; these actions must be 677 * safe. 678 * 679 * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should 680 * be processed normally. 681 * 682 * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be 683 * invoked. In this case, seccomp_phase1 will have set the return value 684 * using syscall_set_return_value. 685 * 686 * If it returns anything else, then the return value should be passed 687 * to seccomp_phase2 from a context in which ptrace hooks are safe. 688 */ 689u32 seccomp_phase1(struct seccomp_data *sd) 690{ 691 int mode = current->seccomp.mode; 692 int this_syscall = sd ? sd->nr : 693 syscall_get_nr(current, task_pt_regs(current)); 694 695 switch (mode) { 696 case SECCOMP_MODE_STRICT: 697 __secure_computing_strict(this_syscall); /* may call do_exit */ 698 return SECCOMP_PHASE1_OK; 699#ifdef CONFIG_SECCOMP_FILTER 700 case SECCOMP_MODE_FILTER: 701 return __seccomp_phase1_filter(this_syscall, sd); 702#endif 703 default: 704 BUG(); 705 } 706} 707 708/** 709 * seccomp_phase2() - finish slow path seccomp work for the current syscall 710 * @phase1_result: The return value from seccomp_phase1() 711 * 712 * This must be called from a context in which ptrace hooks can be used. 713 * 714 * Returns 0 if the syscall should be processed or -1 to skip the syscall. 715 */ 716int seccomp_phase2(u32 phase1_result) 717{ 718 struct pt_regs *regs = task_pt_regs(current); 719 u32 action = phase1_result & SECCOMP_RET_ACTION; 720 int data = phase1_result & SECCOMP_RET_DATA; 721 722 BUG_ON(action != SECCOMP_RET_TRACE); 723 724 audit_seccomp(syscall_get_nr(current, regs), 0, action); 725 726 /* Skip these calls if there is no tracer. */ 727 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 728 syscall_set_return_value(current, regs, 729 -ENOSYS, 0); 730 return -1; 731 } 732 733 /* Allow the BPF to provide the event message */ 734 ptrace_event(PTRACE_EVENT_SECCOMP, data); 735 /* 736 * The delivery of a fatal signal during event 737 * notification may silently skip tracer notification. 738 * Terminating the task now avoids executing a system 739 * call that may not be intended. 740 */ 741 if (fatal_signal_pending(current)) 742 do_exit(SIGSYS); 743 if (syscall_get_nr(current, regs) < 0) 744 return -1; /* Explicit request to skip. */ 745 746 return 0; 747} 748#endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 749 750long prctl_get_seccomp(void) 751{ 752 return current->seccomp.mode; 753} 754 755/** 756 * seccomp_set_mode_strict: internal function for setting strict seccomp 757 * 758 * Once current->seccomp.mode is non-zero, it may not be changed. 759 * 760 * Returns 0 on success or -EINVAL on failure. 761 */ 762static long seccomp_set_mode_strict(void) 763{ 764 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 765 long ret = -EINVAL; 766 767 spin_lock_irq(¤t->sighand->siglock); 768 769 if (!seccomp_may_assign_mode(seccomp_mode)) 770 goto out; 771 772#ifdef TIF_NOTSC 773 disable_TSC(); 774#endif 775 seccomp_assign_mode(current, seccomp_mode); 776 ret = 0; 777 778out: 779 spin_unlock_irq(¤t->sighand->siglock); 780 781 return ret; 782} 783 784#ifdef CONFIG_SECCOMP_FILTER 785/** 786 * seccomp_set_mode_filter: internal function for setting seccomp filter 787 * @flags: flags to change filter behavior 788 * @filter: struct sock_fprog containing filter 789 * 790 * This function may be called repeatedly to install additional filters. 791 * Every filter successfully installed will be evaluated (in reverse order) 792 * for each system call the task makes. 793 * 794 * Once current->seccomp.mode is non-zero, it may not be changed. 795 * 796 * Returns 0 on success or -EINVAL on failure. 797 */ 798static long seccomp_set_mode_filter(unsigned int flags, 799 const char __user *filter) 800{ 801 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 802 struct seccomp_filter *prepared = NULL; 803 long ret = -EINVAL; 804 805 /* Validate flags. */ 806 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 807 return -EINVAL; 808 809 /* Prepare the new filter before holding any locks. */ 810 prepared = seccomp_prepare_user_filter(filter); 811 if (IS_ERR(prepared)) 812 return PTR_ERR(prepared); 813 814 /* 815 * Make sure we cannot change seccomp or nnp state via TSYNC 816 * while another thread is in the middle of calling exec. 817 */ 818 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 819 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 820 goto out_free; 821 822 spin_lock_irq(¤t->sighand->siglock); 823 824 if (!seccomp_may_assign_mode(seccomp_mode)) 825 goto out; 826 827 ret = seccomp_attach_filter(flags, prepared); 828 if (ret) 829 goto out; 830 /* Do not free the successfully attached filter. */ 831 prepared = NULL; 832 833 seccomp_assign_mode(current, seccomp_mode); 834out: 835 spin_unlock_irq(¤t->sighand->siglock); 836 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 837 mutex_unlock(¤t->signal->cred_guard_mutex); 838out_free: 839 seccomp_filter_free(prepared); 840 return ret; 841} 842#else 843static inline long seccomp_set_mode_filter(unsigned int flags, 844 const char __user *filter) 845{ 846 return -EINVAL; 847} 848#endif 849 850/* Common entry point for both prctl and syscall. */ 851static long do_seccomp(unsigned int op, unsigned int flags, 852 const char __user *uargs) 853{ 854 switch (op) { 855 case SECCOMP_SET_MODE_STRICT: 856 if (flags != 0 || uargs != NULL) 857 return -EINVAL; 858 return seccomp_set_mode_strict(); 859 case SECCOMP_SET_MODE_FILTER: 860 return seccomp_set_mode_filter(flags, uargs); 861 default: 862 return -EINVAL; 863 } 864} 865 866SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 867 const char __user *, uargs) 868{ 869 return do_seccomp(op, flags, uargs); 870} 871 872/** 873 * prctl_set_seccomp: configures current->seccomp.mode 874 * @seccomp_mode: requested mode to use 875 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 876 * 877 * Returns 0 on success or -EINVAL on failure. 878 */ 879long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 880{ 881 unsigned int op; 882 char __user *uargs; 883 884 switch (seccomp_mode) { 885 case SECCOMP_MODE_STRICT: 886 op = SECCOMP_SET_MODE_STRICT; 887 /* 888 * Setting strict mode through prctl always ignored filter, 889 * so make sure it is always NULL here to pass the internal 890 * check in do_seccomp(). 891 */ 892 uargs = NULL; 893 break; 894 case SECCOMP_MODE_FILTER: 895 op = SECCOMP_SET_MODE_FILTER; 896 uargs = filter; 897 break; 898 default: 899 return -EINVAL; 900 } 901 902 /* prctl interface doesn't have flags, so they are always zero. */ 903 return do_seccomp(op, 0, uargs); 904} 905