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_data sd_local;
179	u32 ret = SECCOMP_RET_ALLOW;
180	/* Make sure cross-thread synced filter points somewhere sane. */
181	struct seccomp_filter *f =
182			lockless_dereference(current->seccomp.filter);
183
184	/* Ensure unexpected behavior doesn't result in failing open. */
185	if (unlikely(WARN_ON(f == NULL)))
186		return SECCOMP_RET_KILL;
187
188	if (!sd) {
189		populate_seccomp_data(&sd_local);
190		sd = &sd_local;
191	}
192
193	/*
194	 * All filters in the list are evaluated and the lowest BPF return
195	 * value always takes priority (ignoring the DATA).
196	 */
 
197	for (; f; f = f->prev) {
198		u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd);
199
200		if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
201			ret = cur_ret;
 
 
202	}
 
203	return ret;
204}
205#endif /* CONFIG_SECCOMP_FILTER */
206
207static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
208{
209	assert_spin_locked(&current->sighand->siglock);
210
211	if (current->seccomp.mode && current->seccomp.mode != seccomp_mode)
212		return false;
213
214	return true;
215}
216
 
 
217static inline void seccomp_assign_mode(struct task_struct *task,
218				       unsigned long seccomp_mode)
 
219{
220	assert_spin_locked(&task->sighand->siglock);
221
222	task->seccomp.mode = seccomp_mode;
223	/*
224	 * Make sure TIF_SECCOMP cannot be set before the mode (and
225	 * filter) is set.
226	 */
227	smp_mb__before_atomic();
 
 
 
228	set_tsk_thread_flag(task, TIF_SECCOMP);
229}
230
231#ifdef CONFIG_SECCOMP_FILTER
232/* Returns 1 if the parent is an ancestor of the child. */
233static int is_ancestor(struct seccomp_filter *parent,
234		       struct seccomp_filter *child)
235{
236	/* NULL is the root ancestor. */
237	if (parent == NULL)
238		return 1;
239	for (; child; child = child->prev)
240		if (child == parent)
241			return 1;
242	return 0;
243}
244
245/**
246 * seccomp_can_sync_threads: checks if all threads can be synchronized
247 *
248 * Expects sighand and cred_guard_mutex locks to be held.
249 *
250 * Returns 0 on success, -ve on error, or the pid of a thread which was
251 * either not in the correct seccomp mode or it did not have an ancestral
252 * seccomp filter.
253 */
254static inline pid_t seccomp_can_sync_threads(void)
255{
256	struct task_struct *thread, *caller;
257
258	BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
259	assert_spin_locked(&current->sighand->siglock);
260
261	/* Validate all threads being eligible for synchronization. */
262	caller = current;
263	for_each_thread(caller, thread) {
264		pid_t failed;
265
266		/* Skip current, since it is initiating the sync. */
267		if (thread == caller)
268			continue;
269
270		if (thread->seccomp.mode == SECCOMP_MODE_DISABLED ||
271		    (thread->seccomp.mode == SECCOMP_MODE_FILTER &&
272		     is_ancestor(thread->seccomp.filter,
273				 caller->seccomp.filter)))
274			continue;
275
276		/* Return the first thread that cannot be synchronized. */
277		failed = task_pid_vnr(thread);
278		/* If the pid cannot be resolved, then return -ESRCH */
279		if (unlikely(WARN_ON(failed == 0)))
280			failed = -ESRCH;
281		return failed;
282	}
283
284	return 0;
285}
286
287/**
288 * seccomp_sync_threads: sets all threads to use current's filter
289 *
290 * Expects sighand and cred_guard_mutex locks to be held, and for
291 * seccomp_can_sync_threads() to have returned success already
292 * without dropping the locks.
293 *
294 */
295static inline void seccomp_sync_threads(void)
296{
297	struct task_struct *thread, *caller;
298
299	BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
300	assert_spin_locked(&current->sighand->siglock);
301
302	/* Synchronize all threads. */
303	caller = current;
304	for_each_thread(caller, thread) {
305		/* Skip current, since it needs no changes. */
306		if (thread == caller)
307			continue;
308
309		/* Get a task reference for the new leaf node. */
310		get_seccomp_filter(caller);
311		/*
312		 * Drop the task reference to the shared ancestor since
313		 * current's path will hold a reference.  (This also
314		 * allows a put before the assignment.)
315		 */
316		put_seccomp_filter(thread);
317		smp_store_release(&thread->seccomp.filter,
318				  caller->seccomp.filter);
319
320		/*
321		 * Don't let an unprivileged task work around
322		 * the no_new_privs restriction by creating
323		 * a thread that sets it up, enters seccomp,
324		 * then dies.
325		 */
326		if (task_no_new_privs(caller))
327			task_set_no_new_privs(thread);
328
329		/*
330		 * Opt the other thread into seccomp if needed.
331		 * As threads are considered to be trust-realm
332		 * equivalent (see ptrace_may_access), it is safe to
333		 * allow one thread to transition the other.
334		 */
335		if (thread->seccomp.mode == SECCOMP_MODE_DISABLED)
336			seccomp_assign_mode(thread, SECCOMP_MODE_FILTER);
 
337	}
338}
339
340/**
341 * seccomp_prepare_filter: Prepares a seccomp filter for use.
342 * @fprog: BPF program to install
343 *
344 * Returns filter on success or an ERR_PTR on failure.
345 */
346static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
347{
348	struct seccomp_filter *sfilter;
349	int ret;
350	const bool save_orig = config_enabled(CONFIG_CHECKPOINT_RESTORE);
351
352	if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
353		return ERR_PTR(-EINVAL);
354
355	BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter));
356
357	/*
358	 * Installing a seccomp filter requires that the task has
359	 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
360	 * This avoids scenarios where unprivileged tasks can affect the
361	 * behavior of privileged children.
362	 */
363	if (!task_no_new_privs(current) &&
364	    security_capable_noaudit(current_cred(), current_user_ns(),
365				     CAP_SYS_ADMIN) != 0)
366		return ERR_PTR(-EACCES);
367
368	/* Allocate a new seccomp_filter */
369	sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN);
370	if (!sfilter)
371		return ERR_PTR(-ENOMEM);
372
 
373	ret = bpf_prog_create_from_user(&sfilter->prog, fprog,
374					seccomp_check_filter, save_orig);
375	if (ret < 0) {
376		kfree(sfilter);
377		return ERR_PTR(ret);
378	}
379
380	atomic_set(&sfilter->usage, 1);
381
382	return sfilter;
383}
384
385/**
386 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog
387 * @user_filter: pointer to the user data containing a sock_fprog.
388 *
389 * Returns 0 on success and non-zero otherwise.
390 */
391static struct seccomp_filter *
392seccomp_prepare_user_filter(const char __user *user_filter)
393{
394	struct sock_fprog fprog;
395	struct seccomp_filter *filter = ERR_PTR(-EFAULT);
396
397#ifdef CONFIG_COMPAT
398	if (in_compat_syscall()) {
399		struct compat_sock_fprog fprog32;
400		if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
401			goto out;
402		fprog.len = fprog32.len;
403		fprog.filter = compat_ptr(fprog32.filter);
404	} else /* falls through to the if below. */
405#endif
406	if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
407		goto out;
408	filter = seccomp_prepare_filter(&fprog);
409out:
410	return filter;
411}
412
413/**
414 * seccomp_attach_filter: validate and attach filter
415 * @flags:  flags to change filter behavior
416 * @filter: seccomp filter to add to the current process
417 *
418 * Caller must be holding current->sighand->siglock lock.
419 *
420 * Returns 0 on success, -ve on error.
 
 
 
421 */
422static long seccomp_attach_filter(unsigned int flags,
423				  struct seccomp_filter *filter)
424{
425	unsigned long total_insns;
426	struct seccomp_filter *walker;
427
428	assert_spin_locked(&current->sighand->siglock);
429
430	/* Validate resulting filter length. */
431	total_insns = filter->prog->len;
432	for (walker = current->seccomp.filter; walker; walker = walker->prev)
433		total_insns += walker->prog->len + 4;  /* 4 instr penalty */
434	if (total_insns > MAX_INSNS_PER_PATH)
435		return -ENOMEM;
436
437	/* If thread sync has been requested, check that it is possible. */
438	if (flags & SECCOMP_FILTER_FLAG_TSYNC) {
439		int ret;
440
441		ret = seccomp_can_sync_threads();
442		if (ret)
443			return ret;
444	}
445
 
 
 
 
446	/*
447	 * If there is an existing filter, make it the prev and don't drop its
448	 * task reference.
449	 */
450	filter->prev = current->seccomp.filter;
451	current->seccomp.filter = filter;
452
453	/* Now that the new filter is in place, synchronize to all threads. */
454	if (flags & SECCOMP_FILTER_FLAG_TSYNC)
455		seccomp_sync_threads();
456
457	return 0;
458}
459
 
 
 
 
 
460/* get_seccomp_filter - increments the reference count of the filter on @tsk */
461void get_seccomp_filter(struct task_struct *tsk)
462{
463	struct seccomp_filter *orig = tsk->seccomp.filter;
464	if (!orig)
465		return;
466	/* Reference count is bounded by the number of total processes. */
467	atomic_inc(&orig->usage);
468}
469
470static inline void seccomp_filter_free(struct seccomp_filter *filter)
471{
472	if (filter) {
473		bpf_prog_destroy(filter->prog);
474		kfree(filter);
475	}
476}
477
478/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
479void put_seccomp_filter(struct task_struct *tsk)
480{
481	struct seccomp_filter *orig = tsk->seccomp.filter;
482	/* Clean up single-reference branches iteratively. */
483	while (orig && atomic_dec_and_test(&orig->usage)) {
484		struct seccomp_filter *freeme = orig;
485		orig = orig->prev;
486		seccomp_filter_free(freeme);
487	}
488}
489
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
490/**
491 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
492 * @syscall: syscall number to send to userland
493 * @reason: filter-supplied reason code to send to userland (via si_errno)
494 *
495 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
496 */
497static void seccomp_send_sigsys(int syscall, int reason)
498{
499	struct siginfo info;
500	memset(&info, 0, sizeof(info));
501	info.si_signo = SIGSYS;
502	info.si_code = SYS_SECCOMP;
503	info.si_call_addr = (void __user *)KSTK_EIP(current);
504	info.si_errno = reason;
505	info.si_arch = syscall_get_arch();
506	info.si_syscall = syscall;
507	force_sig_info(SIGSYS, &info, current);
508}
509#endif	/* CONFIG_SECCOMP_FILTER */
510
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
511/*
512 * Secure computing mode 1 allows only read/write/exit/sigreturn.
513 * To be fully secure this must be combined with rlimit
514 * to limit the stack allocations too.
515 */
516static int mode1_syscalls[] = {
517	__NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
518	0, /* null terminated */
519};
520
521#ifdef CONFIG_COMPAT
522static int mode1_syscalls_32[] = {
523	__NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
524	0, /* null terminated */
525};
526#endif
527
528static void __secure_computing_strict(int this_syscall)
529{
530	int *syscall_whitelist = mode1_syscalls;
531#ifdef CONFIG_COMPAT
532	if (in_compat_syscall())
533		syscall_whitelist = mode1_syscalls_32;
534#endif
535	do {
536		if (*syscall_whitelist == this_syscall)
537			return;
538	} while (*++syscall_whitelist);
539
540#ifdef SECCOMP_DEBUG
541	dump_stack();
542#endif
543	audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL);
544	do_exit(SIGKILL);
545}
546
547#ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER
548void secure_computing_strict(int this_syscall)
549{
550	int mode = current->seccomp.mode;
551
552	if (config_enabled(CONFIG_CHECKPOINT_RESTORE) &&
553	    unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
554		return;
555
556	if (mode == SECCOMP_MODE_DISABLED)
557		return;
558	else if (mode == SECCOMP_MODE_STRICT)
559		__secure_computing_strict(this_syscall);
560	else
561		BUG();
562}
563#else
564int __secure_computing(void)
 
 
565{
566	u32 phase1_result = seccomp_phase1(NULL);
 
 
 
 
 
 
567
568	if (likely(phase1_result == SECCOMP_PHASE1_OK))
569		return 0;
570	else if (likely(phase1_result == SECCOMP_PHASE1_SKIP))
571		return -1;
572	else
573		return seccomp_phase2(phase1_result);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
574}
575
576#ifdef CONFIG_SECCOMP_FILTER
577static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd)
578{
579	u32 filter_ret, action;
 
580	int data;
 
581
582	/*
583	 * Make sure that any changes to mode from another thread have
584	 * been seen after TIF_SECCOMP was seen.
585	 */
586	rmb();
587
588	filter_ret = seccomp_run_filters(sd);
 
 
 
 
 
589	data = filter_ret & SECCOMP_RET_DATA;
590	action = filter_ret & SECCOMP_RET_ACTION;
591
592	switch (action) {
593	case SECCOMP_RET_ERRNO:
594		/* Set low-order bits as an errno, capped at MAX_ERRNO. */
595		if (data > MAX_ERRNO)
596			data = MAX_ERRNO;
597		syscall_set_return_value(current, task_pt_regs(current),
598					 -data, 0);
599		goto skip;
600
601	case SECCOMP_RET_TRAP:
602		/* Show the handler the original registers. */
603		syscall_rollback(current, task_pt_regs(current));
604		/* Let the filter pass back 16 bits of data. */
605		seccomp_send_sigsys(this_syscall, data);
606		goto skip;
607
608	case SECCOMP_RET_TRACE:
609		return filter_ret;  /* Save the rest for phase 2. */
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
610
611	case SECCOMP_RET_ALLOW:
612		return SECCOMP_PHASE1_OK;
 
 
 
 
 
613
614	case SECCOMP_RET_KILL:
 
615	default:
616		audit_seccomp(this_syscall, SIGSYS, action);
617		do_exit(SIGSYS);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
618	}
619
620	unreachable();
621
622skip:
623	audit_seccomp(this_syscall, 0, action);
624	return SECCOMP_PHASE1_SKIP;
 
 
 
 
 
 
625}
626#endif
627
628/**
629 * seccomp_phase1() - run fast path seccomp checks on the current syscall
630 * @arg sd: The seccomp_data or NULL
631 *
632 * This only reads pt_regs via the syscall_xyz helpers.  The only change
633 * it will make to pt_regs is via syscall_set_return_value, and it will
634 * only do that if it returns SECCOMP_PHASE1_SKIP.
635 *
636 * If sd is provided, it will not read pt_regs at all.
637 *
638 * It may also call do_exit or force a signal; these actions must be
639 * safe.
640 *
641 * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should
642 * be processed normally.
643 *
644 * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be
645 * invoked.  In this case, seccomp_phase1 will have set the return value
646 * using syscall_set_return_value.
647 *
648 * If it returns anything else, then the return value should be passed
649 * to seccomp_phase2 from a context in which ptrace hooks are safe.
650 */
651u32 seccomp_phase1(struct seccomp_data *sd)
652{
653	int mode = current->seccomp.mode;
654	int this_syscall = sd ? sd->nr :
655		syscall_get_nr(current, task_pt_regs(current));
656
657	if (config_enabled(CONFIG_CHECKPOINT_RESTORE) &&
658	    unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
659		return SECCOMP_PHASE1_OK;
 
 
 
660
661	switch (mode) {
662	case SECCOMP_MODE_STRICT:
663		__secure_computing_strict(this_syscall);  /* may call do_exit */
664		return SECCOMP_PHASE1_OK;
665#ifdef CONFIG_SECCOMP_FILTER
666	case SECCOMP_MODE_FILTER:
667		return __seccomp_phase1_filter(this_syscall, sd);
668#endif
669	default:
670		BUG();
671	}
672}
673
674/**
675 * seccomp_phase2() - finish slow path seccomp work for the current syscall
676 * @phase1_result: The return value from seccomp_phase1()
677 *
678 * This must be called from a context in which ptrace hooks can be used.
679 *
680 * Returns 0 if the syscall should be processed or -1 to skip the syscall.
681 */
682int seccomp_phase2(u32 phase1_result)
683{
684	struct pt_regs *regs = task_pt_regs(current);
685	u32 action = phase1_result & SECCOMP_RET_ACTION;
686	int data = phase1_result & SECCOMP_RET_DATA;
687
688	BUG_ON(action != SECCOMP_RET_TRACE);
689
690	audit_seccomp(syscall_get_nr(current, regs), 0, action);
691
692	/* Skip these calls if there is no tracer. */
693	if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
694		syscall_set_return_value(current, regs,
695					 -ENOSYS, 0);
696		return -1;
697	}
698
699	/* Allow the BPF to provide the event message */
700	ptrace_event(PTRACE_EVENT_SECCOMP, data);
701	/*
702	 * The delivery of a fatal signal during event
703	 * notification may silently skip tracer notification.
704	 * Terminating the task now avoids executing a system
705	 * call that may not be intended.
706	 */
707	if (fatal_signal_pending(current))
708		do_exit(SIGSYS);
709	if (syscall_get_nr(current, regs) < 0)
710		return -1;  /* Explicit request to skip. */
711
712	return 0;
713}
714#endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */
715
716long prctl_get_seccomp(void)
717{
718	return current->seccomp.mode;
719}
720
721/**
722 * seccomp_set_mode_strict: internal function for setting strict seccomp
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 */
728static long seccomp_set_mode_strict(void)
729{
730	const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
731	long ret = -EINVAL;
732
733	spin_lock_irq(&current->sighand->siglock);
734
735	if (!seccomp_may_assign_mode(seccomp_mode))
736		goto out;
737
738#ifdef TIF_NOTSC
739	disable_TSC();
740#endif
741	seccomp_assign_mode(current, seccomp_mode);
742	ret = 0;
743
744out:
745	spin_unlock_irq(&current->sighand->siglock);
746
747	return ret;
748}
749
750#ifdef CONFIG_SECCOMP_FILTER
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
751/**
752 * seccomp_set_mode_filter: internal function for setting seccomp filter
753 * @flags:  flags to change filter behavior
754 * @filter: struct sock_fprog containing filter
755 *
756 * This function may be called repeatedly to install additional filters.
757 * Every filter successfully installed will be evaluated (in reverse order)
758 * for each system call the task makes.
759 *
760 * Once current->seccomp.mode is non-zero, it may not be changed.
761 *
762 * Returns 0 on success or -EINVAL on failure.
763 */
764static long seccomp_set_mode_filter(unsigned int flags,
765				    const char __user *filter)
766{
767	const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
768	struct seccomp_filter *prepared = NULL;
769	long ret = -EINVAL;
 
 
770
771	/* Validate flags. */
772	if (flags & ~SECCOMP_FILTER_FLAG_MASK)
773		return -EINVAL;
774
 
 
 
 
 
 
 
 
 
 
775	/* Prepare the new filter before holding any locks. */
776	prepared = seccomp_prepare_user_filter(filter);
777	if (IS_ERR(prepared))
778		return PTR_ERR(prepared);
779
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
780	/*
781	 * Make sure we cannot change seccomp or nnp state via TSYNC
782	 * while another thread is in the middle of calling exec.
783	 */
784	if (flags & SECCOMP_FILTER_FLAG_TSYNC &&
785	    mutex_lock_killable(&current->signal->cred_guard_mutex))
786		goto out_free;
787
788	spin_lock_irq(&current->sighand->siglock);
789
790	if (!seccomp_may_assign_mode(seccomp_mode))
791		goto out;
792
793	ret = seccomp_attach_filter(flags, prepared);
794	if (ret)
795		goto out;
796	/* Do not free the successfully attached filter. */
797	prepared = NULL;
798
799	seccomp_assign_mode(current, seccomp_mode);
800out:
801	spin_unlock_irq(&current->sighand->siglock);
802	if (flags & SECCOMP_FILTER_FLAG_TSYNC)
803		mutex_unlock(&current->signal->cred_guard_mutex);
 
 
 
 
 
 
 
 
 
 
 
804out_free:
805	seccomp_filter_free(prepared);
806	return ret;
807}
808#else
809static inline long seccomp_set_mode_filter(unsigned int flags,
810					   const char __user *filter)
811{
812	return -EINVAL;
813}
814#endif
815
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
816/* Common entry point for both prctl and syscall. */
817static long do_seccomp(unsigned int op, unsigned int flags,
818		       const char __user *uargs)
819{
820	switch (op) {
821	case SECCOMP_SET_MODE_STRICT:
822		if (flags != 0 || uargs != NULL)
823			return -EINVAL;
824		return seccomp_set_mode_strict();
825	case SECCOMP_SET_MODE_FILTER:
826		return seccomp_set_mode_filter(flags, uargs);
 
 
 
 
 
 
 
 
 
 
827	default:
828		return -EINVAL;
829	}
830}
831
832SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
833			 const char __user *, uargs)
834{
835	return do_seccomp(op, flags, uargs);
836}
837
838/**
839 * prctl_set_seccomp: configures current->seccomp.mode
840 * @seccomp_mode: requested mode to use
841 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
842 *
843 * Returns 0 on success or -EINVAL on failure.
844 */
845long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
846{
847	unsigned int op;
848	char __user *uargs;
849
850	switch (seccomp_mode) {
851	case SECCOMP_MODE_STRICT:
852		op = SECCOMP_SET_MODE_STRICT;
853		/*
854		 * Setting strict mode through prctl always ignored filter,
855		 * so make sure it is always NULL here to pass the internal
856		 * check in do_seccomp().
857		 */
858		uargs = NULL;
859		break;
860	case SECCOMP_MODE_FILTER:
861		op = SECCOMP_SET_MODE_FILTER;
862		uargs = filter;
863		break;
864	default:
865		return -EINVAL;
866	}
867
868	/* prctl interface doesn't have flags, so they are always zero. */
869	return do_seccomp(op, 0, uargs);
870}
871
872#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
873long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
874			void __user *data)
875{
876	struct seccomp_filter *filter;
877	struct sock_fprog_kern *fprog;
878	long ret;
879	unsigned long count = 0;
880
881	if (!capable(CAP_SYS_ADMIN) ||
882	    current->seccomp.mode != SECCOMP_MODE_DISABLED) {
883		return -EACCES;
884	}
885
 
 
 
 
886	spin_lock_irq(&task->sighand->siglock);
 
887	if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
888		ret = -EINVAL;
889		goto out;
890	}
891
892	filter = task->seccomp.filter;
893	while (filter) {
894		filter = filter->prev;
 
 
 
895		count++;
896	}
897
898	if (filter_off >= count) {
899		ret = -ENOENT;
900		goto out;
901	}
902	count -= filter_off;
903
904	filter = task->seccomp.filter;
905	while (filter && count > 1) {
906		filter = filter->prev;
907		count--;
908	}
909
910	if (WARN_ON(count != 1 || !filter)) {
911		/* The filter tree shouldn't shrink while we're using it. */
912		ret = -ENOENT;
913		goto out;
914	}
915
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
916	fprog = filter->prog->orig_prog;
917	if (!fprog) {
918		/* This must be a new non-cBPF filter, since we save every
919		 * every cBPF filter's orig_prog above when
920		 * CONFIG_CHECKPOINT_RESTORE is enabled.
921		 */
922		ret = -EMEDIUMTYPE;
923		goto out;
924	}
925
926	ret = fprog->len;
927	if (!data)
928		goto out;
929
930	get_seccomp_filter(task);
931	spin_unlock_irq(&task->sighand->siglock);
932
933	if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
934		ret = -EFAULT;
935
936	put_seccomp_filter(task);
 
937	return ret;
 
938
939out:
940	spin_unlock_irq(&task->sighand->siglock);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
941	return ret;
942}
943#endif