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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * linux/kernel/seccomp.c
3 *
4 * Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com>
5 *
Will Drewrye2cfabdf2012-04-12 16:47:57 -05006 * 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.
Linus Torvalds1da177e2005-04-16 15:20:36 -070014 */
15
Will Drewrye2cfabdf2012-04-12 16:47:57 -050016#include <linux/atomic.h>
Eric Paris85e7bac32012-01-03 14:23:05 -050017#include <linux/audit.h>
Roland McGrath5b101742009-02-27 23:25:54 -080018#include <linux/compat.h>
Will Drewrye2cfabdf2012-04-12 16:47:57 -050019#include <linux/sched.h>
20#include <linux/seccomp.h>
Kees Cookc8bee432014-06-27 15:16:33 -070021#include <linux/slab.h>
Kees Cook48dc92b2014-06-25 16:08:24 -070022#include <linux/syscalls.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070023
Andy Lutomirskia4412fc2014-07-21 18:49:14 -070024#ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
Will Drewrye2cfabdf2012-04-12 16:47:57 -050025#include <asm/syscall.h>
Andy Lutomirskia4412fc2014-07-21 18:49:14 -070026#endif
Will Drewrye2cfabdf2012-04-12 16:47:57 -050027
28#ifdef CONFIG_SECCOMP_FILTER
Will Drewrye2cfabdf2012-04-12 16:47:57 -050029#include <linux/filter.h>
Kees Cookc2e1f2e2014-06-05 00:23:17 -070030#include <linux/pid.h>
Will Drewryfb0fadf2012-04-12 16:48:02 -050031#include <linux/ptrace.h>
Will Drewrye2cfabdf2012-04-12 16:47:57 -050032#include <linux/security.h>
Will Drewrye2cfabdf2012-04-12 16:47:57 -050033#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
Fabian Frederick119ce5c2014-06-06 14:37:53 -070045 * @insnsi: the BPF program instructions to evaluate
Will Drewrye2cfabdf2012-04-12 16:47:57 -050046 *
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;
Alexei Starovoitov7ae457c2014-07-30 20:34:16 -070060 struct bpf_prog *prog;
Will Drewrye2cfabdf2012-04-12 16:47:57 -050061};
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
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +010066/*
Will Drewrye2cfabdf2012-04-12 16:47:57 -050067 * Endianness is explicitly ignored and left for BPF program authors to manage
68 * as per the specific architecture.
69 */
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +010070static void populate_seccomp_data(struct seccomp_data *sd)
Will Drewrye2cfabdf2012-04-12 16:47:57 -050071{
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +010072 struct task_struct *task = current;
73 struct pt_regs *regs = task_pt_regs(task);
Daniel Borkmann2eac7642014-04-14 21:02:59 +020074 unsigned long args[6];
Will Drewrye2cfabdf2012-04-12 16:47:57 -050075
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +010076 sd->nr = syscall_get_nr(task, regs);
Linus Torvalds0b747172014-04-12 12:38:53 -070077 sd->arch = syscall_get_arch();
Daniel Borkmann2eac7642014-04-14 21:02:59 +020078 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];
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +010085 sd->instruction_pointer = KSTK_EIP(task);
Will Drewrye2cfabdf2012-04-12 16:47:57 -050086}
87
88/**
89 * seccomp_check_filter - verify seccomp filter code
90 * @filter: filter to verify
91 * @flen: length of filter
92 *
Alexei Starovoitov4df95ff2014-07-30 20:34:14 -070093 * Takes a previously checked filter (by bpf_check_classic) and
Will Drewrye2cfabdf2012-04-12 16:47:57 -050094 * 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) {
Daniel Borkmann34805932014-05-29 10:22:50 +0200109 case BPF_LD | BPF_W | BPF_ABS:
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +0100110 ftest->code = BPF_LDX | BPF_W | BPF_ABS;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500111 /* 32-bit aligned and not out of bounds. */
112 if (k >= sizeof(struct seccomp_data) || k & 3)
113 return -EINVAL;
114 continue;
Daniel Borkmann34805932014-05-29 10:22:50 +0200115 case BPF_LD | BPF_W | BPF_LEN:
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +0100116 ftest->code = BPF_LD | BPF_IMM;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500117 ftest->k = sizeof(struct seccomp_data);
118 continue;
Daniel Borkmann34805932014-05-29 10:22:50 +0200119 case BPF_LDX | BPF_W | BPF_LEN:
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +0100120 ftest->code = BPF_LDX | BPF_IMM;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500121 ftest->k = sizeof(struct seccomp_data);
122 continue;
123 /* Explicitly include allowed calls. */
Daniel Borkmann34805932014-05-29 10:22:50 +0200124 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:
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500162 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 */
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700176static u32 seccomp_run_filters(struct seccomp_data *sd)
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500177{
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700178 struct seccomp_data sd_local;
Will Drewryacf3b2c2012-04-12 16:47:59 -0500179 u32 ret = SECCOMP_RET_ALLOW;
Pranith Kumar8225d382014-11-21 10:06:01 -0500180 /* Make sure cross-thread synced filter points somewhere sane. */
181 struct seccomp_filter *f =
182 lockless_dereference(current->seccomp.filter);
Will Drewryacf3b2c2012-04-12 16:47:59 -0500183
184 /* Ensure unexpected behavior doesn't result in failing open. */
Kees Cook3ba25302014-06-27 15:01:35 -0700185 if (unlikely(WARN_ON(f == NULL)))
Will Drewryacf3b2c2012-04-12 16:47:59 -0500186 return SECCOMP_RET_KILL;
187
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700188 if (!sd) {
189 populate_seccomp_data(&sd_local);
190 sd = &sd_local;
191 }
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +0100192
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500193 /*
194 * All filters in the list are evaluated and the lowest BPF return
Will Drewryacf3b2c2012-04-12 16:47:59 -0500195 * value always takes priority (ignoring the DATA).
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500196 */
Kees Cook3ba25302014-06-27 15:01:35 -0700197 for (; f; f = f->prev) {
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700198 u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd);
Alexei Starovoitov8f577ca2014-05-13 19:50:47 -0700199
Will Drewryacf3b2c2012-04-12 16:47:59 -0500200 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
201 ret = cur_ret;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500202 }
203 return ret;
204}
Kees Cook1f41b4502014-06-25 15:38:02 -0700205#endif /* CONFIG_SECCOMP_FILTER */
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500206
Kees Cook1f41b4502014-06-25 15:38:02 -0700207static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
208{
Guenter Roeck69f6a342014-08-10 20:50:30 -0700209 assert_spin_locked(&current->sighand->siglock);
Kees Cookdbd952122014-06-27 15:18:48 -0700210
Kees Cook1f41b4502014-06-25 15:38:02 -0700211 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode)
212 return false;
213
214 return true;
215}
216
Kees Cook3ba25302014-06-27 15:01:35 -0700217static inline void seccomp_assign_mode(struct task_struct *task,
218 unsigned long seccomp_mode)
Kees Cook1f41b4502014-06-25 15:38:02 -0700219{
Guenter Roeck69f6a342014-08-10 20:50:30 -0700220 assert_spin_locked(&task->sighand->siglock);
Kees Cookdbd952122014-06-27 15:18:48 -0700221
Kees Cook3ba25302014-06-27 15:01:35 -0700222 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);
Kees Cook1f41b4502014-06-25 15:38:02 -0700229}
230
231#ifdef CONFIG_SECCOMP_FILTER
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700232/* 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));
Guenter Roeck69f6a342014-08-10 20:50:30 -0700259 assert_spin_locked(&current->sighand->siglock);
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700260
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));
Guenter Roeck69f6a342014-08-10 20:50:30 -0700300 assert_spin_locked(&current->sighand->siglock);
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700301
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 * Opt the other thread into seccomp if needed.
321 * As threads are considered to be trust-realm
322 * equivalent (see ptrace_may_access), it is safe to
323 * allow one thread to transition the other.
324 */
325 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) {
326 /*
327 * Don't let an unprivileged task work around
328 * the no_new_privs restriction by creating
329 * a thread that sets it up, enters seccomp,
330 * then dies.
331 */
332 if (task_no_new_privs(caller))
333 task_set_no_new_privs(thread);
334
335 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER);
336 }
337 }
338}
339
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500340/**
Kees Cookc8bee432014-06-27 15:16:33 -0700341 * seccomp_prepare_filter: Prepares a seccomp filter for use.
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500342 * @fprog: BPF program to install
343 *
Kees Cookc8bee432014-06-27 15:16:33 -0700344 * Returns filter on success or an ERR_PTR on failure.
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500345 */
Kees Cookc8bee432014-06-27 15:16:33 -0700346static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500347{
Daniel Borkmannac67eb22015-05-06 16:12:30 +0200348 struct seccomp_filter *sfilter;
349 int ret;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500350
351 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
Kees Cookc8bee432014-06-27 15:16:33 -0700352 return ERR_PTR(-EINVAL);
Nicolas Schichand9e12f42e2015-05-06 16:12:28 +0200353
Kees Cookc8bee432014-06-27 15:16:33 -0700354 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter));
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500355
356 /*
Fabian Frederick119ce5c2014-06-06 14:37:53 -0700357 * Installing a seccomp filter requires that the task has
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500358 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
359 * This avoids scenarios where unprivileged tasks can affect the
360 * behavior of privileged children.
361 */
Kees Cook1d4457f2014-05-21 15:23:46 -0700362 if (!task_no_new_privs(current) &&
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500363 security_capable_noaudit(current_cred(), current_user_ns(),
364 CAP_SYS_ADMIN) != 0)
Kees Cookc8bee432014-06-27 15:16:33 -0700365 return ERR_PTR(-EACCES);
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500366
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +0100367 /* Allocate a new seccomp_filter */
Daniel Borkmannac67eb22015-05-06 16:12:30 +0200368 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN);
369 if (!sfilter)
Nicolas Schichand9e12f42e2015-05-06 16:12:28 +0200370 return ERR_PTR(-ENOMEM);
Daniel Borkmannac67eb22015-05-06 16:12:30 +0200371
372 ret = bpf_prog_create_from_user(&sfilter->prog, fprog,
373 seccomp_check_filter);
374 if (ret < 0) {
375 kfree(sfilter);
376 return ERR_PTR(ret);
Nicolas Schichand9e12f42e2015-05-06 16:12:28 +0200377 }
Alexei Starovoitovbd4cf0e2014-03-28 18:58:25 +0100378
Daniel Borkmannac67eb22015-05-06 16:12:30 +0200379 atomic_set(&sfilter->usage, 1);
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500380
Daniel Borkmannac67eb22015-05-06 16:12:30 +0200381 return sfilter;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500382}
383
384/**
Kees Cookc8bee432014-06-27 15:16:33 -0700385 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500386 * @user_filter: pointer to the user data containing a sock_fprog.
387 *
388 * Returns 0 on success and non-zero otherwise.
389 */
Kees Cookc8bee432014-06-27 15:16:33 -0700390static struct seccomp_filter *
391seccomp_prepare_user_filter(const char __user *user_filter)
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500392{
393 struct sock_fprog fprog;
Kees Cookc8bee432014-06-27 15:16:33 -0700394 struct seccomp_filter *filter = ERR_PTR(-EFAULT);
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500395
396#ifdef CONFIG_COMPAT
397 if (is_compat_task()) {
398 struct compat_sock_fprog fprog32;
399 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
400 goto out;
401 fprog.len = fprog32.len;
402 fprog.filter = compat_ptr(fprog32.filter);
403 } else /* falls through to the if below. */
404#endif
405 if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
406 goto out;
Kees Cookc8bee432014-06-27 15:16:33 -0700407 filter = seccomp_prepare_filter(&fprog);
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500408out:
Kees Cookc8bee432014-06-27 15:16:33 -0700409 return filter;
410}
411
412/**
413 * seccomp_attach_filter: validate and attach filter
414 * @flags: flags to change filter behavior
415 * @filter: seccomp filter to add to the current process
416 *
Kees Cookdbd952122014-06-27 15:18:48 -0700417 * Caller must be holding current->sighand->siglock lock.
418 *
Kees Cookc8bee432014-06-27 15:16:33 -0700419 * Returns 0 on success, -ve on error.
420 */
421static long seccomp_attach_filter(unsigned int flags,
422 struct seccomp_filter *filter)
423{
424 unsigned long total_insns;
425 struct seccomp_filter *walker;
426
Guenter Roeck69f6a342014-08-10 20:50:30 -0700427 assert_spin_locked(&current->sighand->siglock);
Kees Cookdbd952122014-06-27 15:18:48 -0700428
Kees Cookc8bee432014-06-27 15:16:33 -0700429 /* Validate resulting filter length. */
430 total_insns = filter->prog->len;
431 for (walker = current->seccomp.filter; walker; walker = walker->prev)
432 total_insns += walker->prog->len + 4; /* 4 instr penalty */
433 if (total_insns > MAX_INSNS_PER_PATH)
434 return -ENOMEM;
435
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700436 /* If thread sync has been requested, check that it is possible. */
437 if (flags & SECCOMP_FILTER_FLAG_TSYNC) {
438 int ret;
439
440 ret = seccomp_can_sync_threads();
441 if (ret)
442 return ret;
443 }
444
Kees Cookc8bee432014-06-27 15:16:33 -0700445 /*
446 * If there is an existing filter, make it the prev and don't drop its
447 * task reference.
448 */
449 filter->prev = current->seccomp.filter;
450 current->seccomp.filter = filter;
451
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700452 /* Now that the new filter is in place, synchronize to all threads. */
453 if (flags & SECCOMP_FILTER_FLAG_TSYNC)
454 seccomp_sync_threads();
455
Kees Cookc8bee432014-06-27 15:16:33 -0700456 return 0;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500457}
458
459/* get_seccomp_filter - increments the reference count of the filter on @tsk */
460void get_seccomp_filter(struct task_struct *tsk)
461{
462 struct seccomp_filter *orig = tsk->seccomp.filter;
463 if (!orig)
464 return;
465 /* Reference count is bounded by the number of total processes. */
466 atomic_inc(&orig->usage);
467}
468
Kees Cookc8bee432014-06-27 15:16:33 -0700469static inline void seccomp_filter_free(struct seccomp_filter *filter)
470{
471 if (filter) {
Linus Torvaldsae045e22014-08-06 09:38:14 -0700472 bpf_prog_free(filter->prog);
Kees Cookc8bee432014-06-27 15:16:33 -0700473 kfree(filter);
474 }
475}
476
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500477/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
478void put_seccomp_filter(struct task_struct *tsk)
479{
480 struct seccomp_filter *orig = tsk->seccomp.filter;
481 /* Clean up single-reference branches iteratively. */
482 while (orig && atomic_dec_and_test(&orig->usage)) {
483 struct seccomp_filter *freeme = orig;
484 orig = orig->prev;
Kees Cookc8bee432014-06-27 15:16:33 -0700485 seccomp_filter_free(freeme);
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500486 }
487}
Will Drewrybb6ea432012-04-12 16:48:01 -0500488
489/**
490 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
491 * @syscall: syscall number to send to userland
492 * @reason: filter-supplied reason code to send to userland (via si_errno)
493 *
494 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
495 */
496static void seccomp_send_sigsys(int syscall, int reason)
497{
498 struct siginfo info;
499 memset(&info, 0, sizeof(info));
500 info.si_signo = SIGSYS;
501 info.si_code = SYS_SECCOMP;
502 info.si_call_addr = (void __user *)KSTK_EIP(current);
503 info.si_errno = reason;
Eric Paris5e937a92014-03-11 12:48:43 -0400504 info.si_arch = syscall_get_arch();
Will Drewrybb6ea432012-04-12 16:48:01 -0500505 info.si_syscall = syscall;
506 force_sig_info(SIGSYS, &info, current);
507}
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500508#endif /* CONFIG_SECCOMP_FILTER */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700509
510/*
511 * Secure computing mode 1 allows only read/write/exit/sigreturn.
512 * To be fully secure this must be combined with rlimit
513 * to limit the stack allocations too.
514 */
515static int mode1_syscalls[] = {
516 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
517 0, /* null terminated */
518};
519
Roland McGrath5b101742009-02-27 23:25:54 -0800520#ifdef CONFIG_COMPAT
Linus Torvalds1da177e2005-04-16 15:20:36 -0700521static int mode1_syscalls_32[] = {
522 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
523 0, /* null terminated */
524};
525#endif
526
Andy Lutomirskia4412fc2014-07-21 18:49:14 -0700527static void __secure_computing_strict(int this_syscall)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700528{
Andy Lutomirskia4412fc2014-07-21 18:49:14 -0700529 int *syscall_whitelist = mode1_syscalls;
530#ifdef CONFIG_COMPAT
531 if (is_compat_task())
532 syscall_whitelist = mode1_syscalls_32;
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
Tycho Andersen13c4a902015-06-13 09:02:48 -0600551 if (config_enabled(CONFIG_CHECKPOINT_RESTORE) &&
552 unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
553 return;
554
Kees Cook221272f2015-06-15 15:29:16 -0700555 if (mode == SECCOMP_MODE_DISABLED)
Andy Lutomirskia4412fc2014-07-21 18:49:14 -0700556 return;
557 else if (mode == SECCOMP_MODE_STRICT)
558 __secure_computing_strict(this_syscall);
559 else
560 BUG();
561}
562#else
563int __secure_computing(void)
564{
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700565 u32 phase1_result = seccomp_phase1(NULL);
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700566
567 if (likely(phase1_result == SECCOMP_PHASE1_OK))
568 return 0;
569 else if (likely(phase1_result == SECCOMP_PHASE1_SKIP))
570 return -1;
571 else
572 return seccomp_phase2(phase1_result);
573}
574
575#ifdef CONFIG_SECCOMP_FILTER
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700576static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd)
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700577{
578 u32 filter_ret, action;
579 int data;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700580
Kees Cook3ba25302014-06-27 15:01:35 -0700581 /*
582 * Make sure that any changes to mode from another thread have
583 * been seen after TIF_SECCOMP was seen.
584 */
585 rmb();
586
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700587 filter_ret = seccomp_run_filters(sd);
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700588 data = filter_ret & SECCOMP_RET_DATA;
589 action = filter_ret & SECCOMP_RET_ACTION;
Andy Lutomirski87b526d2012-10-01 11:40:45 -0700590
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700591 switch (action) {
592 case SECCOMP_RET_ERRNO:
Kees Cook580c57f2015-02-17 13:48:00 -0800593 /* Set low-order bits as an errno, capped at MAX_ERRNO. */
594 if (data > MAX_ERRNO)
595 data = MAX_ERRNO;
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700596 syscall_set_return_value(current, task_pt_regs(current),
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700597 -data, 0);
598 goto skip;
599
600 case SECCOMP_RET_TRAP:
601 /* Show the handler the original registers. */
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700602 syscall_rollback(current, task_pt_regs(current));
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700603 /* Let the filter pass back 16 bits of data. */
604 seccomp_send_sigsys(this_syscall, data);
605 goto skip;
606
607 case SECCOMP_RET_TRACE:
608 return filter_ret; /* Save the rest for phase 2. */
609
610 case SECCOMP_RET_ALLOW:
611 return SECCOMP_PHASE1_OK;
612
613 case SECCOMP_RET_KILL:
614 default:
615 audit_seccomp(this_syscall, SIGSYS, action);
616 do_exit(SIGSYS);
Will Drewry8156b452012-04-17 14:48:58 -0500617 }
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700618
619 unreachable();
620
621skip:
622 audit_seccomp(this_syscall, 0, action);
623 return SECCOMP_PHASE1_SKIP;
624}
625#endif
626
627/**
628 * seccomp_phase1() - run fast path seccomp checks on the current syscall
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700629 * @arg sd: The seccomp_data or NULL
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700630 *
631 * This only reads pt_regs via the syscall_xyz helpers. The only change
632 * it will make to pt_regs is via syscall_set_return_value, and it will
633 * only do that if it returns SECCOMP_PHASE1_SKIP.
634 *
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700635 * If sd is provided, it will not read pt_regs at all.
636 *
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700637 * It may also call do_exit or force a signal; these actions must be
638 * safe.
639 *
640 * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should
641 * be processed normally.
642 *
643 * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be
644 * invoked. In this case, seccomp_phase1 will have set the return value
645 * using syscall_set_return_value.
646 *
647 * If it returns anything else, then the return value should be passed
648 * to seccomp_phase2 from a context in which ptrace hooks are safe.
649 */
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700650u32 seccomp_phase1(struct seccomp_data *sd)
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700651{
652 int mode = current->seccomp.mode;
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700653 int this_syscall = sd ? sd->nr :
654 syscall_get_nr(current, task_pt_regs(current));
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700655
Tycho Andersen13c4a902015-06-13 09:02:48 -0600656 if (config_enabled(CONFIG_CHECKPOINT_RESTORE) &&
657 unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
658 return SECCOMP_PHASE1_OK;
659
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700660 switch (mode) {
661 case SECCOMP_MODE_STRICT:
662 __secure_computing_strict(this_syscall); /* may call do_exit */
663 return SECCOMP_PHASE1_OK;
664#ifdef CONFIG_SECCOMP_FILTER
665 case SECCOMP_MODE_FILTER:
Andy Lutomirskid39bd002014-07-21 18:49:16 -0700666 return __seccomp_phase1_filter(this_syscall, sd);
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500667#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -0700668 default:
669 BUG();
670 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700671}
Andrea Arcangeli1d9d02f2007-07-15 23:41:32 -0700672
Andy Lutomirski13aa72f2014-07-21 18:49:15 -0700673/**
674 * seccomp_phase2() - finish slow path seccomp work for the current syscall
675 * @phase1_result: The return value from seccomp_phase1()
676 *
677 * This must be called from a context in which ptrace hooks can be used.
678 *
679 * Returns 0 if the syscall should be processed or -1 to skip the syscall.
680 */
681int seccomp_phase2(u32 phase1_result)
682{
683 struct pt_regs *regs = task_pt_regs(current);
684 u32 action = phase1_result & SECCOMP_RET_ACTION;
685 int data = phase1_result & SECCOMP_RET_DATA;
686
687 BUG_ON(action != SECCOMP_RET_TRACE);
688
689 audit_seccomp(syscall_get_nr(current, regs), 0, action);
690
691 /* Skip these calls if there is no tracer. */
692 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
693 syscall_set_return_value(current, regs,
694 -ENOSYS, 0);
695 return -1;
696 }
697
698 /* Allow the BPF to provide the event message */
699 ptrace_event(PTRACE_EVENT_SECCOMP, data);
700 /*
701 * The delivery of a fatal signal during event
702 * notification may silently skip tracer notification.
703 * Terminating the task now avoids executing a system
704 * call that may not be intended.
705 */
706 if (fatal_signal_pending(current))
707 do_exit(SIGSYS);
708 if (syscall_get_nr(current, regs) < 0)
709 return -1; /* Explicit request to skip. */
710
711 return 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700712}
Andy Lutomirskia4412fc2014-07-21 18:49:14 -0700713#endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */
Andrea Arcangeli1d9d02f2007-07-15 23:41:32 -0700714
715long prctl_get_seccomp(void)
716{
717 return current->seccomp.mode;
718}
719
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500720/**
Kees Cook3b23dd12014-06-25 15:55:25 -0700721 * seccomp_set_mode_strict: internal function for setting strict seccomp
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500722 *
723 * Once current->seccomp.mode is non-zero, it may not be changed.
724 *
725 * Returns 0 on success or -EINVAL on failure.
726 */
Kees Cook3b23dd12014-06-25 15:55:25 -0700727static long seccomp_set_mode_strict(void)
Andrea Arcangeli1d9d02f2007-07-15 23:41:32 -0700728{
Kees Cook3b23dd12014-06-25 15:55:25 -0700729 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500730 long ret = -EINVAL;
Andrea Arcangeli1d9d02f2007-07-15 23:41:32 -0700731
Kees Cookdbd952122014-06-27 15:18:48 -0700732 spin_lock_irq(&current->sighand->siglock);
733
Kees Cook1f41b4502014-06-25 15:38:02 -0700734 if (!seccomp_may_assign_mode(seccomp_mode))
Andrea Arcangeli1d9d02f2007-07-15 23:41:32 -0700735 goto out;
736
Andrea Arcangelicf99aba2007-07-15 23:41:33 -0700737#ifdef TIF_NOTSC
Kees Cook3b23dd12014-06-25 15:55:25 -0700738 disable_TSC();
Andrea Arcangelicf99aba2007-07-15 23:41:33 -0700739#endif
Kees Cook3ba25302014-06-27 15:01:35 -0700740 seccomp_assign_mode(current, seccomp_mode);
Kees Cook3b23dd12014-06-25 15:55:25 -0700741 ret = 0;
742
743out:
Kees Cookdbd952122014-06-27 15:18:48 -0700744 spin_unlock_irq(&current->sighand->siglock);
Kees Cook3b23dd12014-06-25 15:55:25 -0700745
746 return ret;
747}
748
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500749#ifdef CONFIG_SECCOMP_FILTER
Kees Cook3b23dd12014-06-25 15:55:25 -0700750/**
751 * seccomp_set_mode_filter: internal function for setting seccomp filter
Kees Cook48dc92b2014-06-25 16:08:24 -0700752 * @flags: flags to change filter behavior
Kees Cook3b23dd12014-06-25 15:55:25 -0700753 * @filter: struct sock_fprog containing filter
754 *
755 * This function may be called repeatedly to install additional filters.
756 * Every filter successfully installed will be evaluated (in reverse order)
757 * for each system call the task makes.
758 *
759 * Once current->seccomp.mode is non-zero, it may not be changed.
760 *
761 * Returns 0 on success or -EINVAL on failure.
762 */
Kees Cook48dc92b2014-06-25 16:08:24 -0700763static long seccomp_set_mode_filter(unsigned int flags,
764 const char __user *filter)
Kees Cook3b23dd12014-06-25 15:55:25 -0700765{
766 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
Kees Cookc8bee432014-06-27 15:16:33 -0700767 struct seccomp_filter *prepared = NULL;
Kees Cook3b23dd12014-06-25 15:55:25 -0700768 long ret = -EINVAL;
769
Kees Cook48dc92b2014-06-25 16:08:24 -0700770 /* Validate flags. */
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700771 if (flags & ~SECCOMP_FILTER_FLAG_MASK)
Kees Cookdbd952122014-06-27 15:18:48 -0700772 return -EINVAL;
Kees Cook48dc92b2014-06-25 16:08:24 -0700773
Kees Cookc8bee432014-06-27 15:16:33 -0700774 /* Prepare the new filter before holding any locks. */
775 prepared = seccomp_prepare_user_filter(filter);
776 if (IS_ERR(prepared))
777 return PTR_ERR(prepared);
778
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700779 /*
780 * Make sure we cannot change seccomp or nnp state via TSYNC
781 * while another thread is in the middle of calling exec.
782 */
783 if (flags & SECCOMP_FILTER_FLAG_TSYNC &&
784 mutex_lock_killable(&current->signal->cred_guard_mutex))
785 goto out_free;
786
Kees Cookdbd952122014-06-27 15:18:48 -0700787 spin_lock_irq(&current->sighand->siglock);
788
Kees Cook3b23dd12014-06-25 15:55:25 -0700789 if (!seccomp_may_assign_mode(seccomp_mode))
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500790 goto out;
Kees Cook3b23dd12014-06-25 15:55:25 -0700791
Kees Cookc8bee432014-06-27 15:16:33 -0700792 ret = seccomp_attach_filter(flags, prepared);
Kees Cook3b23dd12014-06-25 15:55:25 -0700793 if (ret)
794 goto out;
Kees Cookc8bee432014-06-27 15:16:33 -0700795 /* Do not free the successfully attached filter. */
796 prepared = NULL;
Andrea Arcangeli1d9d02f2007-07-15 23:41:32 -0700797
Kees Cook3ba25302014-06-27 15:01:35 -0700798 seccomp_assign_mode(current, seccomp_mode);
Will Drewrye2cfabdf2012-04-12 16:47:57 -0500799out:
Kees Cookdbd952122014-06-27 15:18:48 -0700800 spin_unlock_irq(&current->sighand->siglock);
Kees Cookc2e1f2e2014-06-05 00:23:17 -0700801 if (flags & SECCOMP_FILTER_FLAG_TSYNC)
802 mutex_unlock(&current->signal->cred_guard_mutex);
803out_free:
Kees Cookc8bee432014-06-27 15:16:33 -0700804 seccomp_filter_free(prepared);
Andrea Arcangeli1d9d02f2007-07-15 23:41:32 -0700805 return ret;
806}
Kees Cook3b23dd12014-06-25 15:55:25 -0700807#else
Kees Cook48dc92b2014-06-25 16:08:24 -0700808static inline long seccomp_set_mode_filter(unsigned int flags,
809 const char __user *filter)
Kees Cook3b23dd12014-06-25 15:55:25 -0700810{
811 return -EINVAL;
812}
813#endif
Kees Cookd78ab022014-05-21 15:02:11 -0700814
Kees Cook48dc92b2014-06-25 16:08:24 -0700815/* Common entry point for both prctl and syscall. */
816static long do_seccomp(unsigned int op, unsigned int flags,
817 const char __user *uargs)
818{
819 switch (op) {
820 case SECCOMP_SET_MODE_STRICT:
821 if (flags != 0 || uargs != NULL)
822 return -EINVAL;
823 return seccomp_set_mode_strict();
824 case SECCOMP_SET_MODE_FILTER:
825 return seccomp_set_mode_filter(flags, uargs);
826 default:
827 return -EINVAL;
828 }
829}
830
831SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
832 const char __user *, uargs)
833{
834 return do_seccomp(op, flags, uargs);
835}
836
Kees Cookd78ab022014-05-21 15:02:11 -0700837/**
838 * prctl_set_seccomp: configures current->seccomp.mode
839 * @seccomp_mode: requested mode to use
840 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
841 *
842 * Returns 0 on success or -EINVAL on failure.
843 */
844long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
845{
Kees Cook48dc92b2014-06-25 16:08:24 -0700846 unsigned int op;
847 char __user *uargs;
848
Kees Cook3b23dd12014-06-25 15:55:25 -0700849 switch (seccomp_mode) {
850 case SECCOMP_MODE_STRICT:
Kees Cook48dc92b2014-06-25 16:08:24 -0700851 op = SECCOMP_SET_MODE_STRICT;
852 /*
853 * Setting strict mode through prctl always ignored filter,
854 * so make sure it is always NULL here to pass the internal
855 * check in do_seccomp().
856 */
857 uargs = NULL;
858 break;
Kees Cook3b23dd12014-06-25 15:55:25 -0700859 case SECCOMP_MODE_FILTER:
Kees Cook48dc92b2014-06-25 16:08:24 -0700860 op = SECCOMP_SET_MODE_FILTER;
861 uargs = filter;
862 break;
Kees Cook3b23dd12014-06-25 15:55:25 -0700863 default:
864 return -EINVAL;
865 }
Kees Cook48dc92b2014-06-25 16:08:24 -0700866
867 /* prctl interface doesn't have flags, so they are always zero. */
868 return do_seccomp(op, 0, uargs);
Kees Cookd78ab022014-05-21 15:02:11 -0700869}