kernel/seccomp.c

   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 /* #define SECCOMP_DEBUG 1 */
  25
  26 #ifdef CONFIG_SECCOMP_FILTER
  27 #include <asm/syscall.h>
  28 #include <linux/filter.h>
  29 #include <linux/ptrace.h>
  30 #include <linux/security.h>
  31 #include <linux/tracehook.h>
  32 #include <linux/uaccess.h>
  33
  34 /**
  35  * struct seccomp_filter - container for seccomp BPF programs
  36  *
  37  * @usage: reference count to manage the object lifetime.
  38  *         get/put helpers should be used when accessing an instance
  39  *         outside of a lifetime-guarded section.  In general, this
  40  *         is only needed for handling filters shared across tasks.
  41  * @prev: points to a previously installed, or inherited, filter
  42  * @len: the number of instructions in the program
  43  * @insnsi: the BPF program instructions to evaluate
  44  *
  45  * seccomp_filter objects are organized in a tree linked via the @prev
  46  * pointer.  For any task, it appears to be a singly-linked list starting
  47  * with current->seccomp.filter, the most recently attached or inherited filter.
  48  * However, multiple filters may share a @prev node, by way of fork(), which
  49  * results in a unidirectional tree existing in memory.  This is similar to
  50  * how namespaces work.
  51  *
  52  * seccomp_filter objects should never be modified after being attached
  53  * to a task_struct (other than @usage).
  54  */
  55 struct seccomp_filter {
  56         atomic_t usage;
  57         struct seccomp_filter *prev;
  58         struct sk_filter *prog;
  59 };
  60
  61 /* Limit any path through the tree to 256KB worth of instructions. */
  62 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
  63
  64 /*
  65  * Endianness is explicitly ignored and left for BPF program authors to manage
  66  * as per the specific architecture.
  67  */
  68 static void populate_seccomp_data(struct seccomp_data *sd)
  69 {
  70         struct task_struct *task = current;
  71         struct pt_regs *regs = task_pt_regs(task);
  72         unsigned long args[6];
  73
  74         sd->nr = syscall_get_nr(task, regs);
  75         sd->arch = syscall_get_arch();
  76         syscall_get_arguments(task, regs, 0, 6, args);
  77         sd->args[0] = args[0];
  78         sd->args[1] = args[1];
  79         sd->args[2] = args[2];
  80         sd->args[3] = args[3];
  81         sd->args[4] = args[4];
  82         sd->args[5] = args[5];
  83         sd->instruction_pointer = KSTK_EIP(task);
  84 }
  85
  86 /**
  87  *      seccomp_check_filter - verify seccomp filter code
  88  *      @filter: filter to verify
  89  *      @flen: length of filter
  90  *
  91  * Takes a previously checked filter (by sk_chk_filter) and
  92  * redirects all filter code that loads struct sk_buff data
  93  * and related data through seccomp_bpf_load.  It also
  94  * enforces length and alignment checking of those loads.
  95  *
  96  * Returns 0 if the rule set is legal or -EINVAL if not.
  97  */
  98 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
  99 {
 100         int pc;
 101         for (pc = 0; pc < flen; pc++) {
 102                 struct sock_filter *ftest = &filter[pc];
 103                 u16 code = ftest->code;
 104                 u32 k = ftest->k;
 105
 106                 switch (code) {
 107                 case BPF_LD | BPF_W | BPF_ABS:
 108                         ftest->code = BPF_LDX | BPF_W | BPF_ABS;
 109                         /* 32-bit aligned and not out of bounds. */
 110                         if (k >= sizeof(struct seccomp_data) || k & 3)
 111                                 return -EINVAL;
 112                         continue;
 113                 case BPF_LD | BPF_W | BPF_LEN:
 114                         ftest->code = BPF_LD | BPF_IMM;
 115                         ftest->k = sizeof(struct seccomp_data);
 116                         continue;
 117                 case BPF_LDX | BPF_W | BPF_LEN:
 118                         ftest->code = BPF_LDX | BPF_IMM;
 119                         ftest->k = sizeof(struct seccomp_data);
 120                         continue;
 121                 /* Explicitly include allowed calls. */
 122                 case BPF_RET | BPF_K:
 123                 case BPF_RET | BPF_A:
 124                 case BPF_ALU | BPF_ADD | BPF_K:
 125                 case BPF_ALU | BPF_ADD | BPF_X:
 126                 case BPF_ALU | BPF_SUB | BPF_K:
 127                 case BPF_ALU | BPF_SUB | BPF_X:
 128                 case BPF_ALU | BPF_MUL | BPF_K:
 129                 case BPF_ALU | BPF_MUL | BPF_X:
 130                 case BPF_ALU | BPF_DIV | BPF_K:
 131                 case BPF_ALU | BPF_DIV | BPF_X:
 132                 case BPF_ALU | BPF_AND | BPF_K:
 133                 case BPF_ALU | BPF_AND | BPF_X:
 134                 case BPF_ALU | BPF_OR | BPF_K:
 135                 case BPF_ALU | BPF_OR | BPF_X:
 136                 case BPF_ALU | BPF_XOR | BPF_K:
 137                 case BPF_ALU | BPF_XOR | BPF_X:
 138                 case BPF_ALU | BPF_LSH | BPF_K:
 139                 case BPF_ALU | BPF_LSH | BPF_X:
 140                 case BPF_ALU | BPF_RSH | BPF_K:
 141                 case BPF_ALU | BPF_RSH | BPF_X:
 142                 case BPF_ALU | BPF_NEG:
 143                 case BPF_LD | BPF_IMM:
 144                 case BPF_LDX | BPF_IMM:
 145                 case BPF_MISC | BPF_TAX:
 146                 case BPF_MISC | BPF_TXA:
 147                 case BPF_LD | BPF_MEM:
 148                 case BPF_LDX | BPF_MEM:
 149                 case BPF_ST:
 150                 case BPF_STX:
 151                 case BPF_JMP | BPF_JA:
 152                 case BPF_JMP | BPF_JEQ | BPF_K:
 153                 case BPF_JMP | BPF_JEQ | BPF_X:
 154                 case BPF_JMP | BPF_JGE | BPF_K:
 155                 case BPF_JMP | BPF_JGE | BPF_X:
 156                 case BPF_JMP | BPF_JGT | BPF_K:
 157                 case BPF_JMP | BPF_JGT | BPF_X:
 158                 case BPF_JMP | BPF_JSET | BPF_K:
 159                 case BPF_JMP | BPF_JSET | BPF_X:
 160                         continue;
 161                 default:
 162                         return -EINVAL;
 163                 }
 164         }
 165         return 0;
 166 }
 167
 168 /**
 169  * seccomp_run_filters - evaluates all seccomp filters against @syscall
 170  * @syscall: number of the current system call
 171  *
 172  * Returns valid seccomp BPF response codes.
 173  */
 174 static u32 seccomp_run_filters(int syscall)
 175 {
 176         struct seccomp_filter *f;
 177         struct seccomp_data sd;
 178         u32 ret = SECCOMP_RET_ALLOW;
 179
 180         /* Ensure unexpected behavior doesn't result in failing open. */
 181         if (WARN_ON(current->seccomp.filter == NULL))
 182                 return SECCOMP_RET_KILL;
 183
 184         populate_seccomp_data(&sd);
 185
 186         /*
 187          * All filters in the list are evaluated and the lowest BPF return
 188          * value always takes priority (ignoring the DATA).
 189          */
 190         for (f = current->seccomp.filter; f; f = f->prev) {
 191                 u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);
 192
 193                 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
 194                         ret = cur_ret;
 195         }
 196         return ret;
 197 }
 198 #endif /* CONFIG_SECCOMP_FILTER */
 199
 200 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
 201 {
 202         if (current->seccomp.mode && current->seccomp.mode != seccomp_mode)
 203                 return false;
 204
 205         return true;
 206 }
 207
 208 static inline void seccomp_assign_mode(unsigned long seccomp_mode)
 209 {
 210         current->seccomp.mode = seccomp_mode;
 211         set_tsk_thread_flag(current, TIF_SECCOMP);
 212 }
 213
 214 #ifdef CONFIG_SECCOMP_FILTER
 215 /**
 216  * seccomp_prepare_filter: Prepares a seccomp filter for use.
 217  * @fprog: BPF program to install
 218  *
 219  * Returns filter on success or an ERR_PTR on failure.
 220  */
 221 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
 222 {
 223         struct seccomp_filter *filter;
 224         unsigned long fp_size;
 225         struct sock_filter *fp;
 226         int new_len;
 227         long ret;
 228
 229         if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
 230                 return ERR_PTR(-EINVAL);
 231         BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter));
 232         fp_size = fprog->len * sizeof(struct sock_filter);
 233
 234         /*
 235          * Installing a seccomp filter requires that the task has
 236          * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
 237          * This avoids scenarios where unprivileged tasks can affect the
 238          * behavior of privileged children.
 239          */
 240         if (!task_no_new_privs(current) &&
 241             security_capable_noaudit(current_cred(), current_user_ns(),
 242                                      CAP_SYS_ADMIN) != 0)
 243                 return ERR_PTR(-EACCES);
 244
 245         fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN);
 246         if (!fp)
 247                 return ERR_PTR(-ENOMEM);
 248
 249         /* Copy the instructions from fprog. */
 250         ret = -EFAULT;
 251         if (copy_from_user(fp, fprog->filter, fp_size))
 252                 goto free_prog;
 253
 254         /* Check and rewrite the fprog via the skb checker */
 255         ret = sk_chk_filter(fp, fprog->len);
 256         if (ret)
 257                 goto free_prog;
 258
 259         /* Check and rewrite the fprog for seccomp use */
 260         ret = seccomp_check_filter(fp, fprog->len);
 261         if (ret)
 262                 goto free_prog;
 263
 264         /* Convert 'sock_filter' insns to 'sock_filter_int' insns */
 265         ret = sk_convert_filter(fp, fprog->len, NULL, &new_len);
 266         if (ret)
 267                 goto free_prog;
 268
 269         /* Allocate a new seccomp_filter */
 270         ret = -ENOMEM;
 271         filter = kzalloc(sizeof(struct seccomp_filter),
 272                          GFP_KERNEL|__GFP_NOWARN);
 273         if (!filter)
 274                 goto free_prog;
 275
 276         filter->prog = kzalloc(sk_filter_size(new_len),
 277                                GFP_KERNEL|__GFP_NOWARN);
 278         if (!filter->prog)
 279                 goto free_filter;
 280
 281         ret = sk_convert_filter(fp, fprog->len, filter->prog->insnsi, &new_len);
 282         if (ret)
 283                 goto free_filter_prog;
 284         kfree(fp);
 285
 286         atomic_set(&filter->usage, 1);
 287         filter->prog->len = new_len;
 288
 289         sk_filter_select_runtime(filter->prog);
 290
 291         return filter;
 292
 293 free_filter_prog:
 294         kfree(filter->prog);
 295 free_filter:
 296         kfree(filter);
 297 free_prog:
 298         kfree(fp);
 299         return ERR_PTR(ret);
 300 }
 301
 302 /**
 303  * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog
 304  * @user_filter: pointer to the user data containing a sock_fprog.
 305  *
 306  * Returns 0 on success and non-zero otherwise.
 307  */
 308 static struct seccomp_filter *
 309 seccomp_prepare_user_filter(const char __user *user_filter)
 310 {
 311         struct sock_fprog fprog;
 312         struct seccomp_filter *filter = ERR_PTR(-EFAULT);
 313
 314 #ifdef CONFIG_COMPAT
 315         if (is_compat_task()) {
 316                 struct compat_sock_fprog fprog32;
 317                 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
 318                         goto out;
 319                 fprog.len = fprog32.len;
 320                 fprog.filter = compat_ptr(fprog32.filter);
 321         } else /* falls through to the if below. */
 322 #endif
 323         if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
 324                 goto out;
 325         filter = seccomp_prepare_filter(&fprog);
 326 out:
 327         return filter;
 328 }
 329
 330 /**
 331  * seccomp_attach_filter: validate and attach filter
 332  * @flags:  flags to change filter behavior
 333  * @filter: seccomp filter to add to the current process
 334  *
 335  * Returns 0 on success, -ve on error.
 336  */
 337 static long seccomp_attach_filter(unsigned int flags,
 338                                   struct seccomp_filter *filter)
 339 {
 340         unsigned long total_insns;
 341         struct seccomp_filter *walker;
 342
 343         /* Validate resulting filter length. */
 344         total_insns = filter->prog->len;
 345         for (walker = current->seccomp.filter; walker; walker = walker->prev)
 346                 total_insns += walker->prog->len + 4;  /* 4 instr penalty */
 347         if (total_insns > MAX_INSNS_PER_PATH)
 348                 return -ENOMEM;
 349
 350         /*
 351          * If there is an existing filter, make it the prev and don't drop its
 352          * task reference.
 353          */
 354         filter->prev = current->seccomp.filter;
 355         current->seccomp.filter = filter;
 356
 357         return 0;
 358 }
 359
 360 /* get_seccomp_filter - increments the reference count of the filter on @tsk */
 361 void get_seccomp_filter(struct task_struct *tsk)
 362 {
 363         struct seccomp_filter *orig = tsk->seccomp.filter;
 364         if (!orig)
 365                 return;
 366         /* Reference count is bounded by the number of total processes. */
 367         atomic_inc(&orig->usage);
 368 }
 369
 370 static inline void seccomp_filter_free(struct seccomp_filter *filter)
 371 {
 372         if (filter) {
 373                 sk_filter_free(filter->prog);
 374                 kfree(filter);
 375         }
 376 }
 377
 378 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
 379 void put_seccomp_filter(struct task_struct *tsk)
 380 {
 381         struct seccomp_filter *orig = tsk->seccomp.filter;
 382         /* Clean up single-reference branches iteratively. */
 383         while (orig && atomic_dec_and_test(&orig->usage)) {
 384                 struct seccomp_filter *freeme = orig;
 385                 orig = orig->prev;
 386                 seccomp_filter_free(freeme);
 387         }
 388 }
 389
 390 /**
 391  * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
 392  * @syscall: syscall number to send to userland
 393  * @reason: filter-supplied reason code to send to userland (via si_errno)
 394  *
 395  * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
 396  */
 397 static void seccomp_send_sigsys(int syscall, int reason)
 398 {
 399         struct siginfo info;
 400         memset(&info, 0, sizeof(info));
 401         info.si_signo = SIGSYS;
 402         info.si_code = SYS_SECCOMP;
 403         info.si_call_addr = (void __user *)KSTK_EIP(current);
 404         info.si_errno = reason;
 405         info.si_arch = syscall_get_arch();
 406         info.si_syscall = syscall;
 407         force_sig_info(SIGSYS, &info, current);
 408 }
 409 #endif  /* CONFIG_SECCOMP_FILTER */
 410
 411 /*
 412  * Secure computing mode 1 allows only read/write/exit/sigreturn.
 413  * To be fully secure this must be combined with rlimit
 414  * to limit the stack allocations too.
 415  */
 416 static int mode1_syscalls[] = {
 417         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
 418         0, /* null terminated */
 419 };
 420
 421 #ifdef CONFIG_COMPAT
 422 static int mode1_syscalls_32[] = {
 423         __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
 424         0, /* null terminated */
 425 };
 426 #endif
 427
 428 int __secure_computing(int this_syscall)
 429 {
 430         int mode = current->seccomp.mode;
 431         int exit_sig = 0;
 432         int *syscall;
 433         u32 ret;
 434
 435         switch (mode) {
 436         case SECCOMP_MODE_STRICT:
 437                 syscall = mode1_syscalls;
 438 #ifdef CONFIG_COMPAT
 439                 if (is_compat_task())
 440                         syscall = mode1_syscalls_32;
 441 #endif
 442                 do {
 443                         if (*syscall == this_syscall)
 444                                 return 0;
 445                 } while (*++syscall);
 446                 exit_sig = SIGKILL;
 447                 ret = SECCOMP_RET_KILL;
 448                 break;
 449 #ifdef CONFIG_SECCOMP_FILTER
 450         case SECCOMP_MODE_FILTER: {
 451                 int data;
 452                 struct pt_regs *regs = task_pt_regs(current);
 453                 ret = seccomp_run_filters(this_syscall);
 454                 data = ret & SECCOMP_RET_DATA;
 455                 ret &= SECCOMP_RET_ACTION;
 456                 switch (ret) {
 457                 case SECCOMP_RET_ERRNO:
 458                         /* Set the low-order 16-bits as a errno. */
 459                         syscall_set_return_value(current, regs,
 460                                                  -data, 0);
 461                         goto skip;
 462                 case SECCOMP_RET_TRAP:
 463                         /* Show the handler the original registers. */
 464                         syscall_rollback(current, regs);
 465                         /* Let the filter pass back 16 bits of data. */
 466                         seccomp_send_sigsys(this_syscall, data);
 467                         goto skip;
 468                 case SECCOMP_RET_TRACE:
 469                         /* Skip these calls if there is no tracer. */
 470                         if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
 471                                 syscall_set_return_value(current, regs,
 472                                                          -ENOSYS, 0);
 473                                 goto skip;
 474                         }
 475                         /* Allow the BPF to provide the event message */
 476                         ptrace_event(PTRACE_EVENT_SECCOMP, data);
 477                         /*
 478                          * The delivery of a fatal signal during event
 479                          * notification may silently skip tracer notification.
 480                          * Terminating the task now avoids executing a system
 481                          * call that may not be intended.
 482                          */
 483                         if (fatal_signal_pending(current))
 484                                 break;
 485                         if (syscall_get_nr(current, regs) < 0)
 486                                 goto skip;  /* Explicit request to skip. */
 487
 488                         return 0;
 489                 case SECCOMP_RET_ALLOW:
 490                         return 0;
 491                 case SECCOMP_RET_KILL:
 492                 default:
 493                         break;
 494                 }
 495                 exit_sig = SIGSYS;
 496                 break;
 497         }
 498 #endif
 499         default:
 500                 BUG();
 501         }
 502
 503 #ifdef SECCOMP_DEBUG
 504         dump_stack();
 505 #endif
 506         audit_seccomp(this_syscall, exit_sig, ret);
 507         do_exit(exit_sig);
 508 #ifdef CONFIG_SECCOMP_FILTER
 509 skip:
 510         audit_seccomp(this_syscall, exit_sig, ret);
 511 #endif
 512         return -1;
 513 }
 514
 515 long prctl_get_seccomp(void)
 516 {
 517         return current->seccomp.mode;
 518 }
 519
 520 /**
 521  * seccomp_set_mode_strict: internal function for setting strict seccomp
 522  *
 523  * Once current->seccomp.mode is non-zero, it may not be changed.
 524  *
 525  * Returns 0 on success or -EINVAL on failure.
 526  */
 527 static long seccomp_set_mode_strict(void)
 528 {
 529         const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
 530         long ret = -EINVAL;
 531
 532         if (!seccomp_may_assign_mode(seccomp_mode))
 533                 goto out;
 534
 535 #ifdef TIF_NOTSC
 536         disable_TSC();
 537 #endif
 538         seccomp_assign_mode(seccomp_mode);
 539         ret = 0;
 540
 541 out:
 542
 543         return ret;
 544 }
 545
 546 #ifdef CONFIG_SECCOMP_FILTER
 547 /**
 548  * seccomp_set_mode_filter: internal function for setting seccomp filter
 549  * @flags:  flags to change filter behavior
 550  * @filter: struct sock_fprog containing filter
 551  *
 552  * This function may be called repeatedly to install additional filters.
 553  * Every filter successfully installed will be evaluated (in reverse order)
 554  * for each system call the task makes.
 555  *
 556  * Once current->seccomp.mode is non-zero, it may not be changed.
 557  *
 558  * Returns 0 on success or -EINVAL on failure.
 559  */
 560 static long seccomp_set_mode_filter(unsigned int flags,
 561                                     const char __user *filter)
 562 {
 563         const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
 564         struct seccomp_filter *prepared = NULL;
 565         long ret = -EINVAL;
 566
 567         /* Validate flags. */
 568         if (flags != 0)
 569                 goto out;
 570
 571         /* Prepare the new filter before holding any locks. */
 572         prepared = seccomp_prepare_user_filter(filter);
 573         if (IS_ERR(prepared))
 574                 return PTR_ERR(prepared);
 575
 576         if (!seccomp_may_assign_mode(seccomp_mode))
 577                 goto out;
 578
 579         ret = seccomp_attach_filter(flags, prepared);
 580         if (ret)
 581                 goto out;
 582         /* Do not free the successfully attached filter. */
 583         prepared = NULL;
 584
 585         seccomp_assign_mode(seccomp_mode);
 586 out:
 587         seccomp_filter_free(prepared);
 588         return ret;
 589 }
 590 #else
 591 static inline long seccomp_set_mode_filter(unsigned int flags,
 592                                            const char __user *filter)
 593 {
 594         return -EINVAL;
 595 }
 596 #endif
 597
 598 /* Common entry point for both prctl and syscall. */
 599 static long do_seccomp(unsigned int op, unsigned int flags,
 600                        const char __user *uargs)
 601 {
 602         switch (op) {
 603         case SECCOMP_SET_MODE_STRICT:
 604                 if (flags != 0 || uargs != NULL)
 605                         return -EINVAL;
 606                 return seccomp_set_mode_strict();
 607         case SECCOMP_SET_MODE_FILTER:
 608                 return seccomp_set_mode_filter(flags, uargs);
 609         default:
 610                 return -EINVAL;
 611         }
 612 }
 613
 614 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
 615                          const char __user *, uargs)
 616 {
 617         return do_seccomp(op, flags, uargs);
 618 }
 619
 620 /**
 621  * prctl_set_seccomp: configures current->seccomp.mode
 622  * @seccomp_mode: requested mode to use
 623  * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
 624  *
 625  * Returns 0 on success or -EINVAL on failure.
 626  */
 627 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
 628 {
 629         unsigned int op;
 630         char __user *uargs;
 631
 632         switch (seccomp_mode) {
 633         case SECCOMP_MODE_STRICT:
 634                 op = SECCOMP_SET_MODE_STRICT;
 635                 /*
 636                  * Setting strict mode through prctl always ignored filter,
 637                  * so make sure it is always NULL here to pass the internal
 638                  * check in do_seccomp().
 639                  */
 640                 uargs = NULL;
 641                 break;
 642         case SECCOMP_MODE_FILTER:
 643                 op = SECCOMP_SET_MODE_FILTER;
 644                 uargs = filter;
 645                 break;
 646         default:
 647                 return -EINVAL;
 648         }
 649
 650         /* prctl interface doesn't have flags, so they are always zero. */
 651         return do_seccomp(op, 0, uargs);
 652 }