Commit | Line | Data |
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1da177e4 LT |
1 | /* |
2 | * linux/kernel/seccomp.c | |
3 | * | |
4 | * Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com> | |
5 | * | |
e2cfabdf WD |
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. | |
1da177e4 LT |
14 | */ |
15 | ||
e2cfabdf | 16 | #include <linux/atomic.h> |
85e7bac3 | 17 | #include <linux/audit.h> |
5b101740 | 18 | #include <linux/compat.h> |
e2cfabdf WD |
19 | #include <linux/sched.h> |
20 | #include <linux/seccomp.h> | |
c8bee430 | 21 | #include <linux/slab.h> |
48dc92b9 | 22 | #include <linux/syscalls.h> |
1da177e4 | 23 | |
a4412fc9 | 24 | #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER |
e2cfabdf | 25 | #include <asm/syscall.h> |
a4412fc9 | 26 | #endif |
e2cfabdf WD |
27 | |
28 | #ifdef CONFIG_SECCOMP_FILTER | |
e2cfabdf | 29 | #include <linux/filter.h> |
c2e1f2e3 | 30 | #include <linux/pid.h> |
fb0fadf9 | 31 | #include <linux/ptrace.h> |
e2cfabdf | 32 | #include <linux/security.h> |
e2cfabdf WD |
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 | |
119ce5c8 | 45 | * @insnsi: the BPF program instructions to evaluate |
e2cfabdf WD |
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 | */ | |
57 | struct seccomp_filter { | |
58 | atomic_t usage; | |
59 | struct seccomp_filter *prev; | |
7ae457c1 | 60 | struct bpf_prog *prog; |
e2cfabdf WD |
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 | ||
bd4cf0ed | 66 | /* |
e2cfabdf WD |
67 | * Endianness is explicitly ignored and left for BPF program authors to manage |
68 | * as per the specific architecture. | |
69 | */ | |
bd4cf0ed | 70 | static void populate_seccomp_data(struct seccomp_data *sd) |
e2cfabdf | 71 | { |
bd4cf0ed AS |
72 | struct task_struct *task = current; |
73 | struct pt_regs *regs = task_pt_regs(task); | |
2eac7648 | 74 | unsigned long args[6]; |
e2cfabdf | 75 | |
bd4cf0ed | 76 | sd->nr = syscall_get_nr(task, regs); |
0b747172 | 77 | sd->arch = syscall_get_arch(); |
2eac7648 DB |
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]; | |
bd4cf0ed | 85 | sd->instruction_pointer = KSTK_EIP(task); |
e2cfabdf WD |
86 | } |
87 | ||
88 | /** | |
89 | * seccomp_check_filter - verify seccomp filter code | |
90 | * @filter: filter to verify | |
91 | * @flen: length of filter | |
92 | * | |
4df95ff4 | 93 | * Takes a previously checked filter (by bpf_check_classic) and |
e2cfabdf WD |
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 | */ | |
100 | static 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) { | |
34805931 | 109 | case BPF_LD | BPF_W | BPF_ABS: |
bd4cf0ed | 110 | ftest->code = BPF_LDX | BPF_W | BPF_ABS; |
e2cfabdf WD |
111 | /* 32-bit aligned and not out of bounds. */ |
112 | if (k >= sizeof(struct seccomp_data) || k & 3) | |
113 | return -EINVAL; | |
114 | continue; | |
34805931 | 115 | case BPF_LD | BPF_W | BPF_LEN: |
bd4cf0ed | 116 | ftest->code = BPF_LD | BPF_IMM; |
e2cfabdf WD |
117 | ftest->k = sizeof(struct seccomp_data); |
118 | continue; | |
34805931 | 119 | case BPF_LDX | BPF_W | BPF_LEN: |
bd4cf0ed | 120 | ftest->code = BPF_LDX | BPF_IMM; |
e2cfabdf WD |
121 | ftest->k = sizeof(struct seccomp_data); |
122 | continue; | |
123 | /* Explicitly include allowed calls. */ | |
34805931 DB |
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: | |
e2cfabdf WD |
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 | */ | |
8112c4f1 | 176 | static u32 seccomp_run_filters(const struct seccomp_data *sd) |
e2cfabdf | 177 | { |
d39bd00d | 178 | struct seccomp_data sd_local; |
acf3b2c7 | 179 | u32 ret = SECCOMP_RET_ALLOW; |
8225d385 PK |
180 | /* Make sure cross-thread synced filter points somewhere sane. */ |
181 | struct seccomp_filter *f = | |
182 | lockless_dereference(current->seccomp.filter); | |
acf3b2c7 WD |
183 | |
184 | /* Ensure unexpected behavior doesn't result in failing open. */ | |
3ba2530c | 185 | if (unlikely(WARN_ON(f == NULL))) |
acf3b2c7 WD |
186 | return SECCOMP_RET_KILL; |
187 | ||
d39bd00d AL |
188 | if (!sd) { |
189 | populate_seccomp_data(&sd_local); | |
190 | sd = &sd_local; | |
191 | } | |
bd4cf0ed | 192 | |
e2cfabdf WD |
193 | /* |
194 | * All filters in the list are evaluated and the lowest BPF return | |
acf3b2c7 | 195 | * value always takes priority (ignoring the DATA). |
e2cfabdf | 196 | */ |
3ba2530c | 197 | for (; f; f = f->prev) { |
d39bd00d | 198 | u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd); |
8f577cad | 199 | |
acf3b2c7 WD |
200 | if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION)) |
201 | ret = cur_ret; | |
e2cfabdf WD |
202 | } |
203 | return ret; | |
204 | } | |
1f41b450 | 205 | #endif /* CONFIG_SECCOMP_FILTER */ |
e2cfabdf | 206 | |
1f41b450 KC |
207 | static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) |
208 | { | |
69f6a34b | 209 | assert_spin_locked(¤t->sighand->siglock); |
dbd95212 | 210 | |
1f41b450 KC |
211 | if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) |
212 | return false; | |
213 | ||
214 | return true; | |
215 | } | |
216 | ||
3ba2530c KC |
217 | static inline void seccomp_assign_mode(struct task_struct *task, |
218 | unsigned long seccomp_mode) | |
1f41b450 | 219 | { |
69f6a34b | 220 | assert_spin_locked(&task->sighand->siglock); |
dbd95212 | 221 | |
3ba2530c KC |
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); | |
1f41b450 KC |
229 | } |
230 | ||
231 | #ifdef CONFIG_SECCOMP_FILTER | |
c2e1f2e3 KC |
232 | /* Returns 1 if the parent is an ancestor of the child. */ |
233 | static 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 | */ | |
254 | static inline pid_t seccomp_can_sync_threads(void) | |
255 | { | |
256 | struct task_struct *thread, *caller; | |
257 | ||
258 | BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); | |
69f6a34b | 259 | assert_spin_locked(¤t->sighand->siglock); |
c2e1f2e3 KC |
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 | */ | |
295 | static inline void seccomp_sync_threads(void) | |
296 | { | |
297 | struct task_struct *thread, *caller; | |
298 | ||
299 | BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); | |
69f6a34b | 300 | assert_spin_locked(¤t->sighand->siglock); |
c2e1f2e3 KC |
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); | |
103502a3 JH |
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 | ||
c2e1f2e3 KC |
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 | */ | |
103502a3 | 335 | if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) |
c2e1f2e3 | 336 | seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); |
c2e1f2e3 KC |
337 | } |
338 | } | |
339 | ||
e2cfabdf | 340 | /** |
c8bee430 | 341 | * seccomp_prepare_filter: Prepares a seccomp filter for use. |
e2cfabdf WD |
342 | * @fprog: BPF program to install |
343 | * | |
c8bee430 | 344 | * Returns filter on success or an ERR_PTR on failure. |
e2cfabdf | 345 | */ |
c8bee430 | 346 | static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) |
e2cfabdf | 347 | { |
ac67eb2c DB |
348 | struct seccomp_filter *sfilter; |
349 | int ret; | |
97f2645f | 350 | const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE); |
e2cfabdf WD |
351 | |
352 | if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) | |
c8bee430 | 353 | return ERR_PTR(-EINVAL); |
d9e12f42 | 354 | |
c8bee430 | 355 | BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); |
e2cfabdf WD |
356 | |
357 | /* | |
119ce5c8 | 358 | * Installing a seccomp filter requires that the task has |
e2cfabdf WD |
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 | */ | |
1d4457f9 | 363 | if (!task_no_new_privs(current) && |
e2cfabdf WD |
364 | security_capable_noaudit(current_cred(), current_user_ns(), |
365 | CAP_SYS_ADMIN) != 0) | |
c8bee430 | 366 | return ERR_PTR(-EACCES); |
e2cfabdf | 367 | |
bd4cf0ed | 368 | /* Allocate a new seccomp_filter */ |
ac67eb2c DB |
369 | sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); |
370 | if (!sfilter) | |
d9e12f42 | 371 | return ERR_PTR(-ENOMEM); |
ac67eb2c DB |
372 | |
373 | ret = bpf_prog_create_from_user(&sfilter->prog, fprog, | |
f8e529ed | 374 | seccomp_check_filter, save_orig); |
ac67eb2c DB |
375 | if (ret < 0) { |
376 | kfree(sfilter); | |
377 | return ERR_PTR(ret); | |
d9e12f42 | 378 | } |
bd4cf0ed | 379 | |
ac67eb2c | 380 | atomic_set(&sfilter->usage, 1); |
e2cfabdf | 381 | |
ac67eb2c | 382 | return sfilter; |
e2cfabdf WD |
383 | } |
384 | ||
385 | /** | |
c8bee430 | 386 | * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog |
e2cfabdf WD |
387 | * @user_filter: pointer to the user data containing a sock_fprog. |
388 | * | |
389 | * Returns 0 on success and non-zero otherwise. | |
390 | */ | |
c8bee430 KC |
391 | static struct seccomp_filter * |
392 | seccomp_prepare_user_filter(const char __user *user_filter) | |
e2cfabdf WD |
393 | { |
394 | struct sock_fprog fprog; | |
c8bee430 | 395 | struct seccomp_filter *filter = ERR_PTR(-EFAULT); |
e2cfabdf WD |
396 | |
397 | #ifdef CONFIG_COMPAT | |
5c38065e | 398 | if (in_compat_syscall()) { |
e2cfabdf WD |
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; | |
c8bee430 | 408 | filter = seccomp_prepare_filter(&fprog); |
e2cfabdf | 409 | out: |
c8bee430 KC |
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 | * | |
dbd95212 KC |
418 | * Caller must be holding current->sighand->siglock lock. |
419 | * | |
c8bee430 KC |
420 | * Returns 0 on success, -ve on error. |
421 | */ | |
422 | static long seccomp_attach_filter(unsigned int flags, | |
423 | struct seccomp_filter *filter) | |
424 | { | |
425 | unsigned long total_insns; | |
426 | struct seccomp_filter *walker; | |
427 | ||
69f6a34b | 428 | assert_spin_locked(¤t->sighand->siglock); |
dbd95212 | 429 | |
c8bee430 KC |
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 | ||
c2e1f2e3 KC |
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 | ||
c8bee430 KC |
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 | ||
c2e1f2e3 KC |
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 | ||
c8bee430 | 457 | return 0; |
e2cfabdf WD |
458 | } |
459 | ||
460 | /* get_seccomp_filter - increments the reference count of the filter on @tsk */ | |
461 | void 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 | ||
c8bee430 KC |
470 | static inline void seccomp_filter_free(struct seccomp_filter *filter) |
471 | { | |
472 | if (filter) { | |
bab18991 | 473 | bpf_prog_destroy(filter->prog); |
c8bee430 KC |
474 | kfree(filter); |
475 | } | |
476 | } | |
477 | ||
e2cfabdf WD |
478 | /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ |
479 | void 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; | |
c8bee430 | 486 | seccomp_filter_free(freeme); |
e2cfabdf WD |
487 | } |
488 | } | |
bb6ea430 WD |
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 | */ | |
497 | static 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; | |
5e937a9a | 505 | info.si_arch = syscall_get_arch(); |
bb6ea430 WD |
506 | info.si_syscall = syscall; |
507 | force_sig_info(SIGSYS, &info, current); | |
508 | } | |
e2cfabdf | 509 | #endif /* CONFIG_SECCOMP_FILTER */ |
1da177e4 LT |
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 | */ | |
cb4253aa | 516 | static const int mode1_syscalls[] = { |
1da177e4 LT |
517 | __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, |
518 | 0, /* null terminated */ | |
519 | }; | |
520 | ||
a4412fc9 | 521 | static void __secure_computing_strict(int this_syscall) |
1da177e4 | 522 | { |
cb4253aa | 523 | const int *syscall_whitelist = mode1_syscalls; |
a4412fc9 | 524 | #ifdef CONFIG_COMPAT |
5c38065e | 525 | if (in_compat_syscall()) |
c983f0e8 | 526 | syscall_whitelist = get_compat_mode1_syscalls(); |
a4412fc9 AL |
527 | #endif |
528 | do { | |
529 | if (*syscall_whitelist == this_syscall) | |
530 | return; | |
531 | } while (*++syscall_whitelist); | |
532 | ||
533 | #ifdef SECCOMP_DEBUG | |
534 | dump_stack(); | |
535 | #endif | |
536 | audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL); | |
537 | do_exit(SIGKILL); | |
538 | } | |
539 | ||
540 | #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER | |
541 | void secure_computing_strict(int this_syscall) | |
542 | { | |
543 | int mode = current->seccomp.mode; | |
544 | ||
97f2645f | 545 | if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && |
13c4a901 TA |
546 | unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) |
547 | return; | |
548 | ||
221272f9 | 549 | if (mode == SECCOMP_MODE_DISABLED) |
a4412fc9 AL |
550 | return; |
551 | else if (mode == SECCOMP_MODE_STRICT) | |
552 | __secure_computing_strict(this_syscall); | |
553 | else | |
554 | BUG(); | |
555 | } | |
556 | #else | |
13aa72f0 AL |
557 | |
558 | #ifdef CONFIG_SECCOMP_FILTER | |
ce6526e8 KC |
559 | static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, |
560 | const bool recheck_after_trace) | |
13aa72f0 AL |
561 | { |
562 | u32 filter_ret, action; | |
563 | int data; | |
1da177e4 | 564 | |
3ba2530c KC |
565 | /* |
566 | * Make sure that any changes to mode from another thread have | |
567 | * been seen after TIF_SECCOMP was seen. | |
568 | */ | |
569 | rmb(); | |
570 | ||
d39bd00d | 571 | filter_ret = seccomp_run_filters(sd); |
13aa72f0 AL |
572 | data = filter_ret & SECCOMP_RET_DATA; |
573 | action = filter_ret & SECCOMP_RET_ACTION; | |
574 | ||
575 | switch (action) { | |
576 | case SECCOMP_RET_ERRNO: | |
580c57f1 KC |
577 | /* Set low-order bits as an errno, capped at MAX_ERRNO. */ |
578 | if (data > MAX_ERRNO) | |
579 | data = MAX_ERRNO; | |
d39bd00d | 580 | syscall_set_return_value(current, task_pt_regs(current), |
13aa72f0 AL |
581 | -data, 0); |
582 | goto skip; | |
583 | ||
584 | case SECCOMP_RET_TRAP: | |
585 | /* Show the handler the original registers. */ | |
d39bd00d | 586 | syscall_rollback(current, task_pt_regs(current)); |
13aa72f0 AL |
587 | /* Let the filter pass back 16 bits of data. */ |
588 | seccomp_send_sigsys(this_syscall, data); | |
589 | goto skip; | |
590 | ||
591 | case SECCOMP_RET_TRACE: | |
ce6526e8 KC |
592 | /* We've been put in this state by the ptracer already. */ |
593 | if (recheck_after_trace) | |
594 | return 0; | |
595 | ||
8112c4f1 KC |
596 | /* ENOSYS these calls if there is no tracer attached. */ |
597 | if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { | |
598 | syscall_set_return_value(current, | |
599 | task_pt_regs(current), | |
600 | -ENOSYS, 0); | |
601 | goto skip; | |
602 | } | |
603 | ||
604 | /* Allow the BPF to provide the event message */ | |
605 | ptrace_event(PTRACE_EVENT_SECCOMP, data); | |
606 | /* | |
607 | * The delivery of a fatal signal during event | |
485a252a KC |
608 | * notification may silently skip tracer notification, |
609 | * which could leave us with a potentially unmodified | |
610 | * syscall that the tracer would have liked to have | |
611 | * changed. Since the process is about to die, we just | |
612 | * force the syscall to be skipped and let the signal | |
613 | * kill the process and correctly handle any tracer exit | |
614 | * notifications. | |
8112c4f1 KC |
615 | */ |
616 | if (fatal_signal_pending(current)) | |
485a252a | 617 | goto skip; |
8112c4f1 KC |
618 | /* Check if the tracer forced the syscall to be skipped. */ |
619 | this_syscall = syscall_get_nr(current, task_pt_regs(current)); | |
620 | if (this_syscall < 0) | |
621 | goto skip; | |
622 | ||
ce6526e8 KC |
623 | /* |
624 | * Recheck the syscall, since it may have changed. This | |
625 | * intentionally uses a NULL struct seccomp_data to force | |
626 | * a reload of all registers. This does not goto skip since | |
627 | * a skip would have already been reported. | |
628 | */ | |
629 | if (__seccomp_filter(this_syscall, NULL, true)) | |
630 | return -1; | |
631 | ||
8112c4f1 | 632 | return 0; |
13aa72f0 AL |
633 | |
634 | case SECCOMP_RET_ALLOW: | |
8112c4f1 | 635 | return 0; |
13aa72f0 AL |
636 | |
637 | case SECCOMP_RET_KILL: | |
638 | default: | |
639 | audit_seccomp(this_syscall, SIGSYS, action); | |
640 | do_exit(SIGSYS); | |
641 | } | |
642 | ||
643 | unreachable(); | |
644 | ||
645 | skip: | |
646 | audit_seccomp(this_syscall, 0, action); | |
8112c4f1 KC |
647 | return -1; |
648 | } | |
649 | #else | |
ce6526e8 KC |
650 | static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, |
651 | const bool recheck_after_trace) | |
8112c4f1 KC |
652 | { |
653 | BUG(); | |
13aa72f0 | 654 | } |
1da177e4 | 655 | #endif |
13aa72f0 | 656 | |
8112c4f1 | 657 | int __secure_computing(const struct seccomp_data *sd) |
13aa72f0 AL |
658 | { |
659 | int mode = current->seccomp.mode; | |
8112c4f1 | 660 | int this_syscall; |
13aa72f0 | 661 | |
97f2645f | 662 | if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && |
13c4a901 | 663 | unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) |
8112c4f1 KC |
664 | return 0; |
665 | ||
666 | this_syscall = sd ? sd->nr : | |
667 | syscall_get_nr(current, task_pt_regs(current)); | |
13c4a901 | 668 | |
13aa72f0 | 669 | switch (mode) { |
e2cfabdf | 670 | case SECCOMP_MODE_STRICT: |
13aa72f0 | 671 | __secure_computing_strict(this_syscall); /* may call do_exit */ |
8112c4f1 | 672 | return 0; |
13aa72f0 | 673 | case SECCOMP_MODE_FILTER: |
ce6526e8 | 674 | return __seccomp_filter(this_syscall, sd, false); |
1da177e4 LT |
675 | default: |
676 | BUG(); | |
677 | } | |
13aa72f0 | 678 | } |
a4412fc9 | 679 | #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ |
1d9d02fe AA |
680 | |
681 | long prctl_get_seccomp(void) | |
682 | { | |
683 | return current->seccomp.mode; | |
684 | } | |
685 | ||
e2cfabdf | 686 | /** |
3b23dd12 | 687 | * seccomp_set_mode_strict: internal function for setting strict seccomp |
e2cfabdf WD |
688 | * |
689 | * Once current->seccomp.mode is non-zero, it may not be changed. | |
690 | * | |
691 | * Returns 0 on success or -EINVAL on failure. | |
692 | */ | |
3b23dd12 | 693 | static long seccomp_set_mode_strict(void) |
1d9d02fe | 694 | { |
3b23dd12 | 695 | const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; |
e2cfabdf | 696 | long ret = -EINVAL; |
1d9d02fe | 697 | |
dbd95212 KC |
698 | spin_lock_irq(¤t->sighand->siglock); |
699 | ||
1f41b450 | 700 | if (!seccomp_may_assign_mode(seccomp_mode)) |
1d9d02fe AA |
701 | goto out; |
702 | ||
cf99abac | 703 | #ifdef TIF_NOTSC |
3b23dd12 | 704 | disable_TSC(); |
cf99abac | 705 | #endif |
3ba2530c | 706 | seccomp_assign_mode(current, seccomp_mode); |
3b23dd12 KC |
707 | ret = 0; |
708 | ||
709 | out: | |
dbd95212 | 710 | spin_unlock_irq(¤t->sighand->siglock); |
3b23dd12 KC |
711 | |
712 | return ret; | |
713 | } | |
714 | ||
e2cfabdf | 715 | #ifdef CONFIG_SECCOMP_FILTER |
3b23dd12 KC |
716 | /** |
717 | * seccomp_set_mode_filter: internal function for setting seccomp filter | |
48dc92b9 | 718 | * @flags: flags to change filter behavior |
3b23dd12 KC |
719 | * @filter: struct sock_fprog containing filter |
720 | * | |
721 | * This function may be called repeatedly to install additional filters. | |
722 | * Every filter successfully installed will be evaluated (in reverse order) | |
723 | * for each system call the task makes. | |
724 | * | |
725 | * Once current->seccomp.mode is non-zero, it may not be changed. | |
726 | * | |
727 | * Returns 0 on success or -EINVAL on failure. | |
728 | */ | |
48dc92b9 KC |
729 | static long seccomp_set_mode_filter(unsigned int flags, |
730 | const char __user *filter) | |
3b23dd12 KC |
731 | { |
732 | const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; | |
c8bee430 | 733 | struct seccomp_filter *prepared = NULL; |
3b23dd12 KC |
734 | long ret = -EINVAL; |
735 | ||
48dc92b9 | 736 | /* Validate flags. */ |
c2e1f2e3 | 737 | if (flags & ~SECCOMP_FILTER_FLAG_MASK) |
dbd95212 | 738 | return -EINVAL; |
48dc92b9 | 739 | |
c8bee430 KC |
740 | /* Prepare the new filter before holding any locks. */ |
741 | prepared = seccomp_prepare_user_filter(filter); | |
742 | if (IS_ERR(prepared)) | |
743 | return PTR_ERR(prepared); | |
744 | ||
c2e1f2e3 KC |
745 | /* |
746 | * Make sure we cannot change seccomp or nnp state via TSYNC | |
747 | * while another thread is in the middle of calling exec. | |
748 | */ | |
749 | if (flags & SECCOMP_FILTER_FLAG_TSYNC && | |
750 | mutex_lock_killable(¤t->signal->cred_guard_mutex)) | |
751 | goto out_free; | |
752 | ||
dbd95212 KC |
753 | spin_lock_irq(¤t->sighand->siglock); |
754 | ||
3b23dd12 KC |
755 | if (!seccomp_may_assign_mode(seccomp_mode)) |
756 | goto out; | |
757 | ||
c8bee430 | 758 | ret = seccomp_attach_filter(flags, prepared); |
3b23dd12 | 759 | if (ret) |
e2cfabdf | 760 | goto out; |
c8bee430 KC |
761 | /* Do not free the successfully attached filter. */ |
762 | prepared = NULL; | |
1d9d02fe | 763 | |
3ba2530c | 764 | seccomp_assign_mode(current, seccomp_mode); |
e2cfabdf | 765 | out: |
dbd95212 | 766 | spin_unlock_irq(¤t->sighand->siglock); |
c2e1f2e3 KC |
767 | if (flags & SECCOMP_FILTER_FLAG_TSYNC) |
768 | mutex_unlock(¤t->signal->cred_guard_mutex); | |
769 | out_free: | |
c8bee430 | 770 | seccomp_filter_free(prepared); |
1d9d02fe AA |
771 | return ret; |
772 | } | |
3b23dd12 | 773 | #else |
48dc92b9 KC |
774 | static inline long seccomp_set_mode_filter(unsigned int flags, |
775 | const char __user *filter) | |
3b23dd12 KC |
776 | { |
777 | return -EINVAL; | |
778 | } | |
779 | #endif | |
d78ab02c | 780 | |
48dc92b9 KC |
781 | /* Common entry point for both prctl and syscall. */ |
782 | static long do_seccomp(unsigned int op, unsigned int flags, | |
783 | const char __user *uargs) | |
784 | { | |
785 | switch (op) { | |
786 | case SECCOMP_SET_MODE_STRICT: | |
787 | if (flags != 0 || uargs != NULL) | |
788 | return -EINVAL; | |
789 | return seccomp_set_mode_strict(); | |
790 | case SECCOMP_SET_MODE_FILTER: | |
791 | return seccomp_set_mode_filter(flags, uargs); | |
792 | default: | |
793 | return -EINVAL; | |
794 | } | |
795 | } | |
796 | ||
797 | SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, | |
798 | const char __user *, uargs) | |
799 | { | |
800 | return do_seccomp(op, flags, uargs); | |
801 | } | |
802 | ||
d78ab02c KC |
803 | /** |
804 | * prctl_set_seccomp: configures current->seccomp.mode | |
805 | * @seccomp_mode: requested mode to use | |
806 | * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER | |
807 | * | |
808 | * Returns 0 on success or -EINVAL on failure. | |
809 | */ | |
810 | long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) | |
811 | { | |
48dc92b9 KC |
812 | unsigned int op; |
813 | char __user *uargs; | |
814 | ||
3b23dd12 KC |
815 | switch (seccomp_mode) { |
816 | case SECCOMP_MODE_STRICT: | |
48dc92b9 KC |
817 | op = SECCOMP_SET_MODE_STRICT; |
818 | /* | |
819 | * Setting strict mode through prctl always ignored filter, | |
820 | * so make sure it is always NULL here to pass the internal | |
821 | * check in do_seccomp(). | |
822 | */ | |
823 | uargs = NULL; | |
824 | break; | |
3b23dd12 | 825 | case SECCOMP_MODE_FILTER: |
48dc92b9 KC |
826 | op = SECCOMP_SET_MODE_FILTER; |
827 | uargs = filter; | |
828 | break; | |
3b23dd12 KC |
829 | default: |
830 | return -EINVAL; | |
831 | } | |
48dc92b9 KC |
832 | |
833 | /* prctl interface doesn't have flags, so they are always zero. */ | |
834 | return do_seccomp(op, 0, uargs); | |
d78ab02c | 835 | } |
f8e529ed TA |
836 | |
837 | #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) | |
838 | long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, | |
839 | void __user *data) | |
840 | { | |
841 | struct seccomp_filter *filter; | |
842 | struct sock_fprog_kern *fprog; | |
843 | long ret; | |
844 | unsigned long count = 0; | |
845 | ||
846 | if (!capable(CAP_SYS_ADMIN) || | |
847 | current->seccomp.mode != SECCOMP_MODE_DISABLED) { | |
848 | return -EACCES; | |
849 | } | |
850 | ||
851 | spin_lock_irq(&task->sighand->siglock); | |
852 | if (task->seccomp.mode != SECCOMP_MODE_FILTER) { | |
853 | ret = -EINVAL; | |
854 | goto out; | |
855 | } | |
856 | ||
857 | filter = task->seccomp.filter; | |
858 | while (filter) { | |
859 | filter = filter->prev; | |
860 | count++; | |
861 | } | |
862 | ||
863 | if (filter_off >= count) { | |
864 | ret = -ENOENT; | |
865 | goto out; | |
866 | } | |
867 | count -= filter_off; | |
868 | ||
869 | filter = task->seccomp.filter; | |
870 | while (filter && count > 1) { | |
871 | filter = filter->prev; | |
872 | count--; | |
873 | } | |
874 | ||
875 | if (WARN_ON(count != 1 || !filter)) { | |
876 | /* The filter tree shouldn't shrink while we're using it. */ | |
877 | ret = -ENOENT; | |
878 | goto out; | |
879 | } | |
880 | ||
881 | fprog = filter->prog->orig_prog; | |
882 | if (!fprog) { | |
470bf1f2 | 883 | /* This must be a new non-cBPF filter, since we save |
f8e529ed TA |
884 | * every cBPF filter's orig_prog above when |
885 | * CONFIG_CHECKPOINT_RESTORE is enabled. | |
886 | */ | |
887 | ret = -EMEDIUMTYPE; | |
888 | goto out; | |
889 | } | |
890 | ||
891 | ret = fprog->len; | |
892 | if (!data) | |
893 | goto out; | |
894 | ||
895 | get_seccomp_filter(task); | |
896 | spin_unlock_irq(&task->sighand->siglock); | |
897 | ||
898 | if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) | |
899 | ret = -EFAULT; | |
900 | ||
901 | put_seccomp_filter(task); | |
902 | return ret; | |
903 | ||
904 | out: | |
905 | spin_unlock_irq(&task->sighand->siglock); | |
906 | return ret; | |
907 | } | |
908 | #endif |