projects/linux·blob v4.11-rc5 · refs

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1/*
2 * linux/kernel/seccomp.c
3 *
4 * Copyright 2004-2005 Andrea Arcangeli <[email protected]>
5 *
6 * Copyright (C) 2012 Google, Inc.
7 * Will Drewry <[email protected]>
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/coredump.h>
20#include <linux/sched.h>
21#include <linux/sched/task_stack.h>
22#include <linux/seccomp.h>
23#include <linux/slab.h>
24#include <linux/syscalls.h>
25
26#ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
27#include <asm/syscall.h>
28#endif
29
30#ifdef CONFIG_SECCOMP_FILTER
31#include <linux/filter.h>
32#include <linux/pid.h>
33#include <linux/ptrace.h>
34#include <linux/security.h>
35#include <linux/tracehook.h>
36#include <linux/uaccess.h>
37
38/**
39 * struct seccomp_filter - container for seccomp BPF programs
40 *
41 * @usage: reference count to manage the object lifetime.
42 * get/put helpers should be used when accessing an instance
43 * outside of a lifetime-guarded section. In general, this
44 * is only needed for handling filters shared across tasks.
45 * @prev: points to a previously installed, or inherited, filter
46 * @prog: the BPF program to evaluate
47 *
48 * seccomp_filter objects are organized in a tree linked via the @prev
49 * pointer. For any task, it appears to be a singly-linked list starting
50 * with current->seccomp.filter, the most recently attached or inherited filter.
51 * However, multiple filters may share a @prev node, by way of fork(), which
52 * results in a unidirectional tree existing in memory. This is similar to
53 * how namespaces work.
54 *
55 * seccomp_filter objects should never be modified after being attached
56 * to a task_struct (other than @usage).
57 */
58struct seccomp_filter {
59 atomic_t usage;
60 struct seccomp_filter *prev;
61 struct bpf_prog *prog;
62};
63
64/* Limit any path through the tree to 256KB worth of instructions. */
65#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
66
67/*
68 * Endianness is explicitly ignored and left for BPF program authors to manage
69 * as per the specific architecture.
70 */
71static void populate_seccomp_data(struct seccomp_data *sd)
72{
73 struct task_struct *task = current;
74 struct pt_regs *regs = task_pt_regs(task);
75 unsigned long args[6];
76
77 sd->nr = syscall_get_nr(task, regs);
78 sd->arch = syscall_get_arch();
79 syscall_get_arguments(task, regs, 0, 6, args);
80 sd->args[0] = args[0];
81 sd->args[1] = args[1];
82 sd->args[2] = args[2];
83 sd->args[3] = args[3];
84 sd->args[4] = args[4];
85 sd->args[5] = args[5];
86 sd->instruction_pointer = KSTK_EIP(task);
87}
88
89/**
90 * seccomp_check_filter - verify seccomp filter code
91 * @filter: filter to verify
92 * @flen: length of filter
93 *
94 * Takes a previously checked filter (by bpf_check_classic) and
95 * redirects all filter code that loads struct sk_buff data
96 * and related data through seccomp_bpf_load. It also
97 * enforces length and alignment checking of those loads.
98 *
99 * Returns 0 if the rule set is legal or -EINVAL if not.
100 */
101static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
102{
103 int pc;
104 for (pc = 0; pc < flen; pc++) {
105 struct sock_filter *ftest = &filter[pc];
106 u16 code = ftest->code;
107 u32 k = ftest->k;
108
109 switch (code) {
110 case BPF_LD | BPF_W | BPF_ABS:
111 ftest->code = BPF_LDX | BPF_W | BPF_ABS;
112 /* 32-bit aligned and not out of bounds. */
113 if (k >= sizeof(struct seccomp_data) || k & 3)
114 return -EINVAL;
115 continue;
116 case BPF_LD | BPF_W | BPF_LEN:
117 ftest->code = BPF_LD | BPF_IMM;
118 ftest->k = sizeof(struct seccomp_data);
119 continue;
120 case BPF_LDX | BPF_W | BPF_LEN:
121 ftest->code = BPF_LDX | BPF_IMM;
122 ftest->k = sizeof(struct seccomp_data);
123 continue;
124 /* Explicitly include allowed calls. */
125 case BPF_RET | BPF_K:
126 case BPF_RET | BPF_A:
127 case BPF_ALU | BPF_ADD | BPF_K:
128 case BPF_ALU | BPF_ADD | BPF_X:
129 case BPF_ALU | BPF_SUB | BPF_K:
130 case BPF_ALU | BPF_SUB | BPF_X:
131 case BPF_ALU | BPF_MUL | BPF_K:
132 case BPF_ALU | BPF_MUL | BPF_X:
133 case BPF_ALU | BPF_DIV | BPF_K:
134 case BPF_ALU | BPF_DIV | BPF_X:
135 case BPF_ALU | BPF_AND | BPF_K:
136 case BPF_ALU | BPF_AND | BPF_X:
137 case BPF_ALU | BPF_OR | BPF_K:
138 case BPF_ALU | BPF_OR | BPF_X:
139 case BPF_ALU | BPF_XOR | BPF_K:
140 case BPF_ALU | BPF_XOR | BPF_X:
141 case BPF_ALU | BPF_LSH | BPF_K:
142 case BPF_ALU | BPF_LSH | BPF_X:
143 case BPF_ALU | BPF_RSH | BPF_K:
144 case BPF_ALU | BPF_RSH | BPF_X:
145 case BPF_ALU | BPF_NEG:
146 case BPF_LD | BPF_IMM:
147 case BPF_LDX | BPF_IMM:
148 case BPF_MISC | BPF_TAX:
149 case BPF_MISC | BPF_TXA:
150 case BPF_LD | BPF_MEM:
151 case BPF_LDX | BPF_MEM:
152 case BPF_ST:
153 case BPF_STX:
154 case BPF_JMP | BPF_JA:
155 case BPF_JMP | BPF_JEQ | BPF_K:
156 case BPF_JMP | BPF_JEQ | BPF_X:
157 case BPF_JMP | BPF_JGE | BPF_K:
158 case BPF_JMP | BPF_JGE | BPF_X:
159 case BPF_JMP | BPF_JGT | BPF_K:
160 case BPF_JMP | BPF_JGT | BPF_X:
161 case BPF_JMP | BPF_JSET | BPF_K:
162 case BPF_JMP | BPF_JSET | BPF_X:
163 continue;
164 default:
165 return -EINVAL;
166 }
167 }
168 return 0;
169}
170
171/**
172 * seccomp_run_filters - evaluates all seccomp filters against @sd
173 * @sd: optional seccomp data to be passed to filters
174 *
175 * Returns valid seccomp BPF response codes.
176 */
177static u32 seccomp_run_filters(const struct seccomp_data *sd)
178{
179 struct seccomp_data sd_local;
180 u32 ret = SECCOMP_RET_ALLOW;
181 /* Make sure cross-thread synced filter points somewhere sane. */
182 struct seccomp_filter *f =
183 lockless_dereference(current->seccomp.filter);
184
185 /* Ensure unexpected behavior doesn't result in failing open. */
186 if (unlikely(WARN_ON(f == NULL)))
187 return SECCOMP_RET_KILL;
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, 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(&current->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(&current->signal->cred_guard_mutex));
260 assert_spin_locked(&current->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(&current->signal->cred_guard_mutex));
301 assert_spin_locked(&current->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 *sfilter;
350 int ret;
351 const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE);
352
353 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
354 return ERR_PTR(-EINVAL);
355
356 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter));
357
358 /*
359 * Installing a seccomp filter requires that the task has
360 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
361 * This avoids scenarios where unprivileged tasks can affect the
362 * behavior of privileged children.
363 */
364 if (!task_no_new_privs(current) &&
365 security_capable_noaudit(current_cred(), current_user_ns(),
366 CAP_SYS_ADMIN) != 0)
367 return ERR_PTR(-EACCES);
368
369 /* Allocate a new seccomp_filter */
370 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN);
371 if (!sfilter)
372 return ERR_PTR(-ENOMEM);
373
374 ret = bpf_prog_create_from_user(&sfilter->prog, fprog,
375 seccomp_check_filter, save_orig);
376 if (ret < 0) {
377 kfree(sfilter);
378 return ERR_PTR(ret);
379 }
380
381 atomic_set(&sfilter->usage, 1);
382
383 return sfilter;
384}
385
386/**
387 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog
388 * @user_filter: pointer to the user data containing a sock_fprog.
389 *
390 * Returns 0 on success and non-zero otherwise.
391 */
392static struct seccomp_filter *
393seccomp_prepare_user_filter(const char __user *user_filter)
394{
395 struct sock_fprog fprog;
396 struct seccomp_filter *filter = ERR_PTR(-EFAULT);
397
398#ifdef CONFIG_COMPAT
399 if (in_compat_syscall()) {
400 struct compat_sock_fprog fprog32;
401 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
402 goto out;
403 fprog.len = fprog32.len;
404 fprog.filter = compat_ptr(fprog32.filter);
405 } else /* falls through to the if below. */
406#endif
407 if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
408 goto out;
409 filter = seccomp_prepare_filter(&fprog);
410out:
411 return filter;
412}
413
414/**
415 * seccomp_attach_filter: validate and attach filter
416 * @flags: flags to change filter behavior
417 * @filter: seccomp filter to add to the current process
418 *
419 * Caller must be holding current->sighand->siglock lock.
420 *
421 * Returns 0 on success, -ve on error.
422 */
423static long seccomp_attach_filter(unsigned int flags,
424 struct seccomp_filter *filter)
425{
426 unsigned long total_insns;
427 struct seccomp_filter *walker;
428
429 assert_spin_locked(&current->sighand->siglock);
430
431 /* Validate resulting filter length. */
432 total_insns = filter->prog->len;
433 for (walker = current->seccomp.filter; walker; walker = walker->prev)
434 total_insns += walker->prog->len + 4; /* 4 instr penalty */
435 if (total_insns > MAX_INSNS_PER_PATH)
436 return -ENOMEM;
437
438 /* If thread sync has been requested, check that it is possible. */
439 if (flags & SECCOMP_FILTER_FLAG_TSYNC) {
440 int ret;
441
442 ret = seccomp_can_sync_threads();
443 if (ret)
444 return ret;
445 }
446
447 /*
448 * If there is an existing filter, make it the prev and don't drop its
449 * task reference.
450 */
451 filter->prev = current->seccomp.filter;
452 current->seccomp.filter = filter;
453
454 /* Now that the new filter is in place, synchronize to all threads. */
455 if (flags & SECCOMP_FILTER_FLAG_TSYNC)
456 seccomp_sync_threads();
457
458 return 0;
459}
460
461/* get_seccomp_filter - increments the reference count of the filter on @tsk */
462void get_seccomp_filter(struct task_struct *tsk)
463{
464 struct seccomp_filter *orig = tsk->seccomp.filter;
465 if (!orig)
466 return;
467 /* Reference count is bounded by the number of total processes. */
468 atomic_inc(&orig->usage);
469}
470
471static inline void seccomp_filter_free(struct seccomp_filter *filter)
472{
473 if (filter) {
474 bpf_prog_destroy(filter->prog);
475 kfree(filter);
476 }
477}
478
479/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
480void put_seccomp_filter(struct task_struct *tsk)
481{
482 struct seccomp_filter *orig = tsk->seccomp.filter;
483 /* Clean up single-reference branches iteratively. */
484 while (orig && atomic_dec_and_test(&orig->usage)) {
485 struct seccomp_filter *freeme = orig;
486 orig = orig->prev;
487 seccomp_filter_free(freeme);
488 }
489}
490
491static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason)
492{
493 memset(info, 0, sizeof(*info));
494 info->si_signo = SIGSYS;
495 info->si_code = SYS_SECCOMP;
496 info->si_call_addr = (void __user *)KSTK_EIP(current);
497 info->si_errno = reason;
498 info->si_arch = syscall_get_arch();
499 info->si_syscall = syscall;
500}
501
502/**
503 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
504 * @syscall: syscall number to send to userland
505 * @reason: filter-supplied reason code to send to userland (via si_errno)
506 *
507 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
508 */
509static void seccomp_send_sigsys(int syscall, int reason)
510{
511 struct siginfo info;
512 seccomp_init_siginfo(&info, syscall, reason);
513 force_sig_info(SIGSYS, &info, current);
514}
515#endif /* CONFIG_SECCOMP_FILTER */
516
517/*
518 * Secure computing mode 1 allows only read/write/exit/sigreturn.
519 * To be fully secure this must be combined with rlimit
520 * to limit the stack allocations too.
521 */
522static const int mode1_syscalls[] = {
523 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
524 0, /* null terminated */
525};
526
527static void __secure_computing_strict(int this_syscall)
528{
529 const int *syscall_whitelist = mode1_syscalls;
530#ifdef CONFIG_COMPAT
531 if (in_compat_syscall())
532 syscall_whitelist = get_compat_mode1_syscalls();
533#endif
534 do {
535 if (*syscall_whitelist == this_syscall)
536 return;
537 } while (*++syscall_whitelist);
538
539#ifdef SECCOMP_DEBUG
540 dump_stack();
541#endif
542 audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL);
543 do_exit(SIGKILL);
544}
545
546#ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER
547void secure_computing_strict(int this_syscall)
548{
549 int mode = current->seccomp.mode;
550
551 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
552 unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
553 return;
554
555 if (mode == SECCOMP_MODE_DISABLED)
556 return;
557 else if (mode == SECCOMP_MODE_STRICT)
558 __secure_computing_strict(this_syscall);
559 else
560 BUG();
561}
562#else
563
564#ifdef CONFIG_SECCOMP_FILTER
565static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
566 const bool recheck_after_trace)
567{
568 u32 filter_ret, action;
569 int data;
570
571 /*
572 * Make sure that any changes to mode from another thread have
573 * been seen after TIF_SECCOMP was seen.
574 */
575 rmb();
576
577 filter_ret = seccomp_run_filters(sd);
578 data = filter_ret & SECCOMP_RET_DATA;
579 action = filter_ret & SECCOMP_RET_ACTION;
580
581 switch (action) {
582 case SECCOMP_RET_ERRNO:
583 /* Set low-order bits as an errno, capped at MAX_ERRNO. */
584 if (data > MAX_ERRNO)
585 data = MAX_ERRNO;
586 syscall_set_return_value(current, task_pt_regs(current),
587 -data, 0);
588 goto skip;
589
590 case SECCOMP_RET_TRAP:
591 /* Show the handler the original registers. */
592 syscall_rollback(current, task_pt_regs(current));
593 /* Let the filter pass back 16 bits of data. */
594 seccomp_send_sigsys(this_syscall, data);
595 goto skip;
596
597 case SECCOMP_RET_TRACE:
598 /* We've been put in this state by the ptracer already. */
599 if (recheck_after_trace)
600 return 0;
601
602 /* ENOSYS these calls if there is no tracer attached. */
603 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
604 syscall_set_return_value(current,
605 task_pt_regs(current),
606 -ENOSYS, 0);
607 goto skip;
608 }
609
610 /* Allow the BPF to provide the event message */
611 ptrace_event(PTRACE_EVENT_SECCOMP, data);
612 /*
613 * The delivery of a fatal signal during event
614 * notification may silently skip tracer notification,
615 * which could leave us with a potentially unmodified
616 * syscall that the tracer would have liked to have
617 * changed. Since the process is about to die, we just
618 * force the syscall to be skipped and let the signal
619 * kill the process and correctly handle any tracer exit
620 * notifications.
621 */
622 if (fatal_signal_pending(current))
623 goto skip;
624 /* Check if the tracer forced the syscall to be skipped. */
625 this_syscall = syscall_get_nr(current, task_pt_regs(current));
626 if (this_syscall < 0)
627 goto skip;
628
629 /*
630 * Recheck the syscall, since it may have changed. This
631 * intentionally uses a NULL struct seccomp_data to force
632 * a reload of all registers. This does not goto skip since
633 * a skip would have already been reported.
634 */
635 if (__seccomp_filter(this_syscall, NULL, true))
636 return -1;
637
638 return 0;
639
640 case SECCOMP_RET_ALLOW:
641 return 0;
642
643 case SECCOMP_RET_KILL:
644 default: {
645 siginfo_t info;
646 audit_seccomp(this_syscall, SIGSYS, action);
647 /* Dump core only if this is the last remaining thread. */
648 if (get_nr_threads(current) == 1) {
649 /* Show the original registers in the dump. */
650 syscall_rollback(current, task_pt_regs(current));
651 /* Trigger a manual coredump since do_exit skips it. */
652 seccomp_init_siginfo(&info, this_syscall, data);
653 do_coredump(&info);
654 }
655 do_exit(SIGSYS);
656 }
657 }
658
659 unreachable();
660
661skip:
662 audit_seccomp(this_syscall, 0, action);
663 return -1;
664}
665#else
666static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
667 const bool recheck_after_trace)
668{
669 BUG();
670}
671#endif
672
673int __secure_computing(const struct seccomp_data *sd)
674{
675 int mode = current->seccomp.mode;
676 int this_syscall;
677
678 if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
679 unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
680 return 0;
681
682 this_syscall = sd ? sd->nr :
683 syscall_get_nr(current, task_pt_regs(current));
684
685 switch (mode) {
686 case SECCOMP_MODE_STRICT:
687 __secure_computing_strict(this_syscall); /* may call do_exit */
688 return 0;
689 case SECCOMP_MODE_FILTER:
690 return __seccomp_filter(this_syscall, sd, false);
691 default:
692 BUG();
693 }
694}
695#endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */
696
697long prctl_get_seccomp(void)
698{
699 return current->seccomp.mode;
700}
701
702/**
703 * seccomp_set_mode_strict: internal function for setting strict seccomp
704 *
705 * Once current->seccomp.mode is non-zero, it may not be changed.
706 *
707 * Returns 0 on success or -EINVAL on failure.
708 */
709static long seccomp_set_mode_strict(void)
710{
711 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
712 long ret = -EINVAL;
713
714 spin_lock_irq(&current->sighand->siglock);
715
716 if (!seccomp_may_assign_mode(seccomp_mode))
717 goto out;
718
719#ifdef TIF_NOTSC
720 disable_TSC();
721#endif
722 seccomp_assign_mode(current, seccomp_mode);
723 ret = 0;
724
725out:
726 spin_unlock_irq(&current->sighand->siglock);
727
728 return ret;
729}
730
731#ifdef CONFIG_SECCOMP_FILTER
732/**
733 * seccomp_set_mode_filter: internal function for setting seccomp filter
734 * @flags: flags to change filter behavior
735 * @filter: struct sock_fprog containing filter
736 *
737 * This function may be called repeatedly to install additional filters.
738 * Every filter successfully installed will be evaluated (in reverse order)
739 * for each system call the task makes.
740 *
741 * Once current->seccomp.mode is non-zero, it may not be changed.
742 *
743 * Returns 0 on success or -EINVAL on failure.
744 */
745static long seccomp_set_mode_filter(unsigned int flags,
746 const char __user *filter)
747{
748 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
749 struct seccomp_filter *prepared = NULL;
750 long ret = -EINVAL;
751
752 /* Validate flags. */
753 if (flags & ~SECCOMP_FILTER_FLAG_MASK)
754 return -EINVAL;
755
756 /* Prepare the new filter before holding any locks. */
757 prepared = seccomp_prepare_user_filter(filter);
758 if (IS_ERR(prepared))
759 return PTR_ERR(prepared);
760
761 /*
762 * Make sure we cannot change seccomp or nnp state via TSYNC
763 * while another thread is in the middle of calling exec.
764 */
765 if (flags & SECCOMP_FILTER_FLAG_TSYNC &&
766 mutex_lock_killable(&current->signal->cred_guard_mutex))
767 goto out_free;
768
769 spin_lock_irq(&current->sighand->siglock);
770
771 if (!seccomp_may_assign_mode(seccomp_mode))
772 goto out;
773
774 ret = seccomp_attach_filter(flags, prepared);
775 if (ret)
776 goto out;
777 /* Do not free the successfully attached filter. */
778 prepared = NULL;
779
780 seccomp_assign_mode(current, seccomp_mode);
781out:
782 spin_unlock_irq(&current->sighand->siglock);
783 if (flags & SECCOMP_FILTER_FLAG_TSYNC)
784 mutex_unlock(&current->signal->cred_guard_mutex);
785out_free:
786 seccomp_filter_free(prepared);
787 return ret;
788}
789#else
790static inline long seccomp_set_mode_filter(unsigned int flags,
791 const char __user *filter)
792{
793 return -EINVAL;
794}
795#endif
796
797/* Common entry point for both prctl and syscall. */
798static long do_seccomp(unsigned int op, unsigned int flags,
799 const char __user *uargs)
800{
801 switch (op) {
802 case SECCOMP_SET_MODE_STRICT:
803 if (flags != 0 || uargs != NULL)
804 return -EINVAL;
805 return seccomp_set_mode_strict();
806 case SECCOMP_SET_MODE_FILTER:
807 return seccomp_set_mode_filter(flags, uargs);
808 default:
809 return -EINVAL;
810 }
811}
812
813SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
814 const char __user *, uargs)
815{
816 return do_seccomp(op, flags, uargs);
817}
818
819/**
820 * prctl_set_seccomp: configures current->seccomp.mode
821 * @seccomp_mode: requested mode to use
822 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
823 *
824 * Returns 0 on success or -EINVAL on failure.
825 */
826long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
827{
828 unsigned int op;
829 char __user *uargs;
830
831 switch (seccomp_mode) {
832 case SECCOMP_MODE_STRICT:
833 op = SECCOMP_SET_MODE_STRICT;
834 /*
835 * Setting strict mode through prctl always ignored filter,
836 * so make sure it is always NULL here to pass the internal
837 * check in do_seccomp().
838 */
839 uargs = NULL;
840 break;
841 case SECCOMP_MODE_FILTER:
842 op = SECCOMP_SET_MODE_FILTER;
843 uargs = filter;
844 break;
845 default:
846 return -EINVAL;
847 }
848
849 /* prctl interface doesn't have flags, so they are always zero. */
850 return do_seccomp(op, 0, uargs);
851}
852
853#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
854long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
855 void __user *data)
856{
857 struct seccomp_filter *filter;
858 struct sock_fprog_kern *fprog;
859 long ret;
860 unsigned long count = 0;
861
862 if (!capable(CAP_SYS_ADMIN) ||
863 current->seccomp.mode != SECCOMP_MODE_DISABLED) {
864 return -EACCES;
865 }
866
867 spin_lock_irq(&task->sighand->siglock);
868 if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
869 ret = -EINVAL;
870 goto out;
871 }
872
873 filter = task->seccomp.filter;
874 while (filter) {
875 filter = filter->prev;
876 count++;
877 }
878
879 if (filter_off >= count) {
880 ret = -ENOENT;
881 goto out;
882 }
883 count -= filter_off;
884
885 filter = task->seccomp.filter;
886 while (filter && count > 1) {
887 filter = filter->prev;
888 count--;
889 }
890
891 if (WARN_ON(count != 1 || !filter)) {
892 /* The filter tree shouldn't shrink while we're using it. */
893 ret = -ENOENT;
894 goto out;
895 }
896
897 fprog = filter->prog->orig_prog;
898 if (!fprog) {
899 /* This must be a new non-cBPF filter, since we save
900 * every cBPF filter's orig_prog above when
901 * CONFIG_CHECKPOINT_RESTORE is enabled.
902 */
903 ret = -EMEDIUMTYPE;
904 goto out;
905 }
906
907 ret = fprog->len;
908 if (!data)
909 goto out;
910
911 get_seccomp_filter(task);
912 spin_unlock_irq(&task->sighand->siglock);
913
914 if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
915 ret = -EFAULT;
916
917 put_seccomp_filter(task);
918 return ret;
919
920out:
921 spin_unlock_irq(&task->sighand->siglock);
922 return ret;
923}
924#endif