~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/kernel/seccomp.c

Version: ~ [ linux-5.6-rc3 ] ~ [ linux-5.5.6 ] ~ [ linux-5.4.22 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.106 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.171 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.214 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.214 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.82 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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 
 22 /* #define SECCOMP_DEBUG 1 */
 23 
 24 #ifdef CONFIG_SECCOMP_FILTER
 25 #include <asm/syscall.h>
 26 #include <linux/filter.h>
 27 #include <linux/ptrace.h>
 28 #include <linux/security.h>
 29 #include <linux/slab.h>
 30 #include <linux/tracehook.h>
 31 #include <linux/uaccess.h>
 32 
 33 /**
 34  * struct seccomp_filter - container for seccomp BPF programs
 35  *
 36  * @usage: reference count to manage the object lifetime.
 37  *         get/put helpers should be used when accessing an instance
 38  *         outside of a lifetime-guarded section.  In general, this
 39  *         is only needed for handling filters shared across tasks.
 40  * @prev: points to a previously installed, or inherited, filter
 41  * @len: the number of instructions in the program
 42  * @insns: the BPF program instructions to evaluate
 43  *
 44  * seccomp_filter objects are organized in a tree linked via the @prev
 45  * pointer.  For any task, it appears to be a singly-linked list starting
 46  * with current->seccomp.filter, the most recently attached or inherited filter.
 47  * However, multiple filters may share a @prev node, by way of fork(), which
 48  * results in a unidirectional tree existing in memory.  This is similar to
 49  * how namespaces work.
 50  *
 51  * seccomp_filter objects should never be modified after being attached
 52  * to a task_struct (other than @usage).
 53  */
 54 struct seccomp_filter {
 55         atomic_t usage;
 56         struct seccomp_filter *prev;
 57         unsigned short len;  /* Instruction count */
 58         struct sock_filter insns[];
 59 };
 60 
 61 /* Limit any path through the tree to 256KB worth of instructions. */
 62 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
 63 
 64 /**
 65  * get_u32 - returns a u32 offset into data
 66  * @data: a unsigned 64 bit value
 67  * @index: 0 or 1 to return the first or second 32-bits
 68  *
 69  * This inline exists to hide the length of unsigned long.  If a 32-bit
 70  * unsigned long is passed in, it will be extended and the top 32-bits will be
 71  * 0. If it is a 64-bit unsigned long, then whatever data is resident will be
 72  * properly returned.
 73  *
 74  * Endianness is explicitly ignored and left for BPF program authors to manage
 75  * as per the specific architecture.
 76  */
 77 static inline u32 get_u32(u64 data, int index)
 78 {
 79         return ((u32 *)&data)[index];
 80 }
 81 
 82 /* Helper for bpf_load below. */
 83 #define BPF_DATA(_name) offsetof(struct seccomp_data, _name)
 84 /**
 85  * bpf_load: checks and returns a pointer to the requested offset
 86  * @off: offset into struct seccomp_data to load from
 87  *
 88  * Returns the requested 32-bits of data.
 89  * seccomp_check_filter() should assure that @off is 32-bit aligned
 90  * and not out of bounds.  Failure to do so is a BUG.
 91  */
 92 u32 seccomp_bpf_load(int off)
 93 {
 94         struct pt_regs *regs = task_pt_regs(current);
 95         if (off == BPF_DATA(nr))
 96                 return syscall_get_nr(current, regs);
 97         if (off == BPF_DATA(arch))
 98                 return syscall_get_arch(current, regs);
 99         if (off >= BPF_DATA(args[0]) && off < BPF_DATA(args[6])) {
100                 unsigned long value;
101                 int arg = (off - BPF_DATA(args[0])) / sizeof(u64);
102                 int index = !!(off % sizeof(u64));
103                 syscall_get_arguments(current, regs, arg, 1, &value);
104                 return get_u32(value, index);
105         }
106         if (off == BPF_DATA(instruction_pointer))
107                 return get_u32(KSTK_EIP(current), 0);
108         if (off == BPF_DATA(instruction_pointer) + sizeof(u32))
109                 return get_u32(KSTK_EIP(current), 1);
110         /* seccomp_check_filter should make this impossible. */
111         BUG();
112 }
113 
114 /**
115  *      seccomp_check_filter - verify seccomp filter code
116  *      @filter: filter to verify
117  *      @flen: length of filter
118  *
119  * Takes a previously checked filter (by sk_chk_filter) and
120  * redirects all filter code that loads struct sk_buff data
121  * and related data through seccomp_bpf_load.  It also
122  * enforces length and alignment checking of those loads.
123  *
124  * Returns 0 if the rule set is legal or -EINVAL if not.
125  */
126 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
127 {
128         int pc;
129         for (pc = 0; pc < flen; pc++) {
130                 struct sock_filter *ftest = &filter[pc];
131                 u16 code = ftest->code;
132                 u32 k = ftest->k;
133 
134                 switch (code) {
135                 case BPF_S_LD_W_ABS:
136                         ftest->code = BPF_S_ANC_SECCOMP_LD_W;
137                         /* 32-bit aligned and not out of bounds. */
138                         if (k >= sizeof(struct seccomp_data) || k & 3)
139                                 return -EINVAL;
140                         continue;
141                 case BPF_S_LD_W_LEN:
142                         ftest->code = BPF_S_LD_IMM;
143                         ftest->k = sizeof(struct seccomp_data);
144                         continue;
145                 case BPF_S_LDX_W_LEN:
146                         ftest->code = BPF_S_LDX_IMM;
147                         ftest->k = sizeof(struct seccomp_data);
148                         continue;
149                 /* Explicitly include allowed calls. */
150                 case BPF_S_RET_K:
151                 case BPF_S_RET_A:
152                 case BPF_S_ALU_ADD_K:
153                 case BPF_S_ALU_ADD_X:
154                 case BPF_S_ALU_SUB_K:
155                 case BPF_S_ALU_SUB_X:
156                 case BPF_S_ALU_MUL_K:
157                 case BPF_S_ALU_MUL_X:
158                 case BPF_S_ALU_DIV_X:
159                 case BPF_S_ALU_AND_K:
160                 case BPF_S_ALU_AND_X:
161                 case BPF_S_ALU_OR_K:
162                 case BPF_S_ALU_OR_X:
163                 case BPF_S_ALU_XOR_K:
164                 case BPF_S_ALU_XOR_X:
165                 case BPF_S_ALU_LSH_K:
166                 case BPF_S_ALU_LSH_X:
167                 case BPF_S_ALU_RSH_K:
168                 case BPF_S_ALU_RSH_X:
169                 case BPF_S_ALU_NEG:
170                 case BPF_S_LD_IMM:
171                 case BPF_S_LDX_IMM:
172                 case BPF_S_MISC_TAX:
173                 case BPF_S_MISC_TXA:
174                 case BPF_S_ALU_DIV_K:
175                 case BPF_S_LD_MEM:
176                 case BPF_S_LDX_MEM:
177                 case BPF_S_ST:
178                 case BPF_S_STX:
179                 case BPF_S_JMP_JA:
180                 case BPF_S_JMP_JEQ_K:
181                 case BPF_S_JMP_JEQ_X:
182                 case BPF_S_JMP_JGE_K:
183                 case BPF_S_JMP_JGE_X:
184                 case BPF_S_JMP_JGT_K:
185                 case BPF_S_JMP_JGT_X:
186                 case BPF_S_JMP_JSET_K:
187                 case BPF_S_JMP_JSET_X:
188                         continue;
189                 default:
190                         return -EINVAL;
191                 }
192         }
193         return 0;
194 }
195 
196 /**
197  * seccomp_run_filters - evaluates all seccomp filters against @syscall
198  * @syscall: number of the current system call
199  *
200  * Returns valid seccomp BPF response codes.
201  */
202 static u32 seccomp_run_filters(int syscall)
203 {
204         struct seccomp_filter *f;
205         u32 ret = SECCOMP_RET_ALLOW;
206 
207         /* Ensure unexpected behavior doesn't result in failing open. */
208         if (WARN_ON(current->seccomp.filter == NULL))
209                 return SECCOMP_RET_KILL;
210 
211         /*
212          * All filters in the list are evaluated and the lowest BPF return
213          * value always takes priority (ignoring the DATA).
214          */
215         for (f = current->seccomp.filter; f; f = f->prev) {
216                 u32 cur_ret = sk_run_filter(NULL, f->insns);
217                 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
218                         ret = cur_ret;
219         }
220         return ret;
221 }
222 
223 /**
224  * seccomp_attach_filter: Attaches a seccomp filter to current.
225  * @fprog: BPF program to install
226  *
227  * Returns 0 on success or an errno on failure.
228  */
229 static long seccomp_attach_filter(struct sock_fprog *fprog)
230 {
231         struct seccomp_filter *filter;
232         unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
233         unsigned long total_insns = fprog->len;
234         long ret;
235 
236         if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
237                 return -EINVAL;
238 
239         for (filter = current->seccomp.filter; filter; filter = filter->prev)
240                 total_insns += filter->len + 4;  /* include a 4 instr penalty */
241         if (total_insns > MAX_INSNS_PER_PATH)
242                 return -ENOMEM;
243 
244         /*
245          * Installing a seccomp filter requires that the task have
246          * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
247          * This avoids scenarios where unprivileged tasks can affect the
248          * behavior of privileged children.
249          */
250         if (!current->no_new_privs &&
251             security_capable_noaudit(current_cred(), current_user_ns(),
252                                      CAP_SYS_ADMIN) != 0)
253                 return -EACCES;
254 
255         /* Allocate a new seccomp_filter */
256         filter = kzalloc(sizeof(struct seccomp_filter) + fp_size,
257                          GFP_KERNEL|__GFP_NOWARN);
258         if (!filter)
259                 return -ENOMEM;
260         atomic_set(&filter->usage, 1);
261         filter->len = fprog->len;
262 
263         /* Copy the instructions from fprog. */
264         ret = -EFAULT;
265         if (copy_from_user(filter->insns, fprog->filter, fp_size))
266                 goto fail;
267 
268         /* Check and rewrite the fprog via the skb checker */
269         ret = sk_chk_filter(filter->insns, filter->len);
270         if (ret)
271                 goto fail;
272 
273         /* Check and rewrite the fprog for seccomp use */
274         ret = seccomp_check_filter(filter->insns, filter->len);
275         if (ret)
276                 goto fail;
277 
278         /*
279          * If there is an existing filter, make it the prev and don't drop its
280          * task reference.
281          */
282         filter->prev = current->seccomp.filter;
283         current->seccomp.filter = filter;
284         return 0;
285 fail:
286         kfree(filter);
287         return ret;
288 }
289 
290 /**
291  * seccomp_attach_user_filter - attaches a user-supplied sock_fprog
292  * @user_filter: pointer to the user data containing a sock_fprog.
293  *
294  * Returns 0 on success and non-zero otherwise.
295  */
296 long seccomp_attach_user_filter(char __user *user_filter)
297 {
298         struct sock_fprog fprog;
299         long ret = -EFAULT;
300 
301 #ifdef CONFIG_COMPAT
302         if (is_compat_task()) {
303                 struct compat_sock_fprog fprog32;
304                 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
305                         goto out;
306                 fprog.len = fprog32.len;
307                 fprog.filter = compat_ptr(fprog32.filter);
308         } else /* falls through to the if below. */
309 #endif
310         if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
311                 goto out;
312         ret = seccomp_attach_filter(&fprog);
313 out:
314         return ret;
315 }
316 
317 /* get_seccomp_filter - increments the reference count of the filter on @tsk */
318 void get_seccomp_filter(struct task_struct *tsk)
319 {
320         struct seccomp_filter *orig = tsk->seccomp.filter;
321         if (!orig)
322                 return;
323         /* Reference count is bounded by the number of total processes. */
324         atomic_inc(&orig->usage);
325 }
326 
327 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
328 void put_seccomp_filter(struct task_struct *tsk)
329 {
330         struct seccomp_filter *orig = tsk->seccomp.filter;
331         /* Clean up single-reference branches iteratively. */
332         while (orig && atomic_dec_and_test(&orig->usage)) {
333                 struct seccomp_filter *freeme = orig;
334                 orig = orig->prev;
335                 kfree(freeme);
336         }
337 }
338 
339 /**
340  * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
341  * @syscall: syscall number to send to userland
342  * @reason: filter-supplied reason code to send to userland (via si_errno)
343  *
344  * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
345  */
346 static void seccomp_send_sigsys(int syscall, int reason)
347 {
348         struct siginfo info;
349         memset(&info, 0, sizeof(info));
350         info.si_signo = SIGSYS;
351         info.si_code = SYS_SECCOMP;
352         info.si_call_addr = (void __user *)KSTK_EIP(current);
353         info.si_errno = reason;
354         info.si_arch = syscall_get_arch(current, task_pt_regs(current));
355         info.si_syscall = syscall;
356         force_sig_info(SIGSYS, &info, current);
357 }
358 #endif  /* CONFIG_SECCOMP_FILTER */
359 
360 /*
361  * Secure computing mode 1 allows only read/write/exit/sigreturn.
362  * To be fully secure this must be combined with rlimit
363  * to limit the stack allocations too.
364  */
365 static int mode1_syscalls[] = {
366         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
367         0, /* null terminated */
368 };
369 
370 #ifdef CONFIG_COMPAT
371 static int mode1_syscalls_32[] = {
372         __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
373         0, /* null terminated */
374 };
375 #endif
376 
377 int __secure_computing(int this_syscall)
378 {
379         int mode = current->seccomp.mode;
380         int exit_sig = 0;
381         int *syscall;
382         u32 ret;
383 
384         switch (mode) {
385         case SECCOMP_MODE_STRICT:
386                 syscall = mode1_syscalls;
387 #ifdef CONFIG_COMPAT
388                 if (is_compat_task())
389                         syscall = mode1_syscalls_32;
390 #endif
391                 do {
392                         if (*syscall == this_syscall)
393                                 return 0;
394                 } while (*++syscall);
395                 exit_sig = SIGKILL;
396                 ret = SECCOMP_RET_KILL;
397                 break;
398 #ifdef CONFIG_SECCOMP_FILTER
399         case SECCOMP_MODE_FILTER: {
400                 int data;
401                 struct pt_regs *regs = task_pt_regs(current);
402                 ret = seccomp_run_filters(this_syscall);
403                 data = ret & SECCOMP_RET_DATA;
404                 ret &= SECCOMP_RET_ACTION;
405                 switch (ret) {
406                 case SECCOMP_RET_ERRNO:
407                         /* Set the low-order 16-bits as a errno. */
408                         syscall_set_return_value(current, regs,
409                                                  -data, 0);
410                         goto skip;
411                 case SECCOMP_RET_TRAP:
412                         /* Show the handler the original registers. */
413                         syscall_rollback(current, regs);
414                         /* Let the filter pass back 16 bits of data. */
415                         seccomp_send_sigsys(this_syscall, data);
416                         goto skip;
417                 case SECCOMP_RET_TRACE:
418                         /* Skip these calls if there is no tracer. */
419                         if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
420                                 syscall_set_return_value(current, regs,
421                                                          -ENOSYS, 0);
422                                 goto skip;
423                         }
424                         /* Allow the BPF to provide the event message */
425                         ptrace_event(PTRACE_EVENT_SECCOMP, data);
426                         /*
427                          * The delivery of a fatal signal during event
428                          * notification may silently skip tracer notification.
429                          * Terminating the task now avoids executing a system
430                          * call that may not be intended.
431                          */
432                         if (fatal_signal_pending(current))
433                                 break;
434                         if (syscall_get_nr(current, regs) < 0)
435                                 goto skip;  /* Explicit request to skip. */
436 
437                         return 0;
438                 case SECCOMP_RET_ALLOW:
439                         return 0;
440                 case SECCOMP_RET_KILL:
441                 default:
442                         break;
443                 }
444                 exit_sig = SIGSYS;
445                 break;
446         }
447 #endif
448         default:
449                 BUG();
450         }
451 
452 #ifdef SECCOMP_DEBUG
453         dump_stack();
454 #endif
455         audit_seccomp(this_syscall, exit_sig, ret);
456         do_exit(exit_sig);
457 #ifdef CONFIG_SECCOMP_FILTER
458 skip:
459         audit_seccomp(this_syscall, exit_sig, ret);
460 #endif
461         return -1;
462 }
463 
464 long prctl_get_seccomp(void)
465 {
466         return current->seccomp.mode;
467 }
468 
469 /**
470  * prctl_set_seccomp: configures current->seccomp.mode
471  * @seccomp_mode: requested mode to use
472  * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
473  *
474  * This function may be called repeatedly with a @seccomp_mode of
475  * SECCOMP_MODE_FILTER to install additional filters.  Every filter
476  * successfully installed will be evaluated (in reverse order) for each system
477  * call the task makes.
478  *
479  * Once current->seccomp.mode is non-zero, it may not be changed.
480  *
481  * Returns 0 on success or -EINVAL on failure.
482  */
483 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
484 {
485         long ret = -EINVAL;
486 
487         if (current->seccomp.mode &&
488             current->seccomp.mode != seccomp_mode)
489                 goto out;
490 
491         switch (seccomp_mode) {
492         case SECCOMP_MODE_STRICT:
493                 ret = 0;
494 #ifdef TIF_NOTSC
495                 disable_TSC();
496 #endif
497                 break;
498 #ifdef CONFIG_SECCOMP_FILTER
499         case SECCOMP_MODE_FILTER:
500                 ret = seccomp_attach_user_filter(filter);
501                 if (ret)
502                         goto out;
503                 break;
504 #endif
505         default:
506                 goto out;
507         }
508 
509         current->seccomp.mode = seccomp_mode;
510         set_thread_flag(TIF_SECCOMP);
511 out:
512         return ret;
513 }
514 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp