1 #include <linux/mm.h> 2 #include <linux/slab.h> 3 #include <linux/string.h> 4 #include <linux/compiler.h> 5 #include <linux/export.h> 6 #include <linux/err.h> 7 #include <linux/sched.h> 8 #include <linux/sched/mm.h> 9 #include <linux/sched/task_stack.h> 10 #include <linux/security.h> 11 #include <linux/swap.h> 12 #include <linux/swapops.h> 13 #include <linux/mman.h> 14 #include <linux/hugetlb.h> 15 #include <linux/vmalloc.h> 16 #include <linux/userfaultfd_k.h> 17 18 #include <linux/uaccess.h> 19 20 #include "internal.h" 21 22 /** 23 * kfree_const - conditionally free memory 24 * @x: pointer to the memory 25 * 26 * Function calls kfree only if @x is not in .rodata section. 27 */ 28 void kfree_const(const void *x) 29 { 30 if (!is_kernel_rodata((unsigned long)x)) 31 kfree(x); 32 } 33 EXPORT_SYMBOL(kfree_const); 34 35 /** 36 * kstrdup - allocate space for and copy an existing string 37 * @s: the string to duplicate 38 * @gfp: the GFP mask used in the kmalloc() call when allocating memory 39 * 40 * Return: newly allocated copy of @s or %NULL in case of error 41 */ 42 char *kstrdup(const char *s, gfp_t gfp) 43 { 44 size_t len; 45 char *buf; 46 47 if (!s) 48 return NULL; 49 50 len = strlen(s) + 1; 51 buf = kmalloc_track_caller(len, gfp); 52 if (buf) 53 memcpy(buf, s, len); 54 return buf; 55 } 56 EXPORT_SYMBOL(kstrdup); 57 58 /** 59 * kstrdup_const - conditionally duplicate an existing const string 60 * @s: the string to duplicate 61 * @gfp: the GFP mask used in the kmalloc() call when allocating memory 62 * 63 * Note: Strings allocated by kstrdup_const should be freed by kfree_const. 64 * 65 * Return: source string if it is in .rodata section otherwise 66 * fallback to kstrdup. 67 */ 68 const char *kstrdup_const(const char *s, gfp_t gfp) 69 { 70 if (is_kernel_rodata((unsigned long)s)) 71 return s; 72 73 return kstrdup(s, gfp); 74 } 75 EXPORT_SYMBOL(kstrdup_const); 76 77 /** 78 * kstrndup - allocate space for and copy an existing string 79 * @s: the string to duplicate 80 * @max: read at most @max chars from @s 81 * @gfp: the GFP mask used in the kmalloc() call when allocating memory 82 * 83 * Note: Use kmemdup_nul() instead if the size is known exactly. 84 * 85 * Return: newly allocated copy of @s or %NULL in case of error 86 */ 87 char *kstrndup(const char *s, size_t max, gfp_t gfp) 88 { 89 size_t len; 90 char *buf; 91 92 if (!s) 93 return NULL; 94 95 len = strnlen(s, max); 96 buf = kmalloc_track_caller(len+1, gfp); 97 if (buf) { 98 memcpy(buf, s, len); 99 buf[len] = '\0'; 100 } 101 return buf; 102 } 103 EXPORT_SYMBOL(kstrndup); 104 105 /** 106 * kmemdup - duplicate region of memory 107 * 108 * @src: memory region to duplicate 109 * @len: memory region length 110 * @gfp: GFP mask to use 111 * 112 * Return: newly allocated copy of @src or %NULL in case of error 113 */ 114 void *kmemdup(const void *src, size_t len, gfp_t gfp) 115 { 116 void *p; 117 118 p = kmalloc_track_caller(len, gfp); 119 if (p) 120 memcpy(p, src, len); 121 return p; 122 } 123 EXPORT_SYMBOL(kmemdup); 124 125 /** 126 * kmemdup_nul - Create a NUL-terminated string from unterminated data 127 * @s: The data to stringify 128 * @len: The size of the data 129 * @gfp: the GFP mask used in the kmalloc() call when allocating memory 130 * 131 * Return: newly allocated copy of @s with NUL-termination or %NULL in 132 * case of error 133 */ 134 char *kmemdup_nul(const char *s, size_t len, gfp_t gfp) 135 { 136 char *buf; 137 138 if (!s) 139 return NULL; 140 141 buf = kmalloc_track_caller(len + 1, gfp); 142 if (buf) { 143 memcpy(buf, s, len); 144 buf[len] = '\0'; 145 } 146 return buf; 147 } 148 EXPORT_SYMBOL(kmemdup_nul); 149 150 /** 151 * memdup_user - duplicate memory region from user space 152 * 153 * @src: source address in user space 154 * @len: number of bytes to copy 155 * 156 * Return: an ERR_PTR() on failure. Result is physically 157 * contiguous, to be freed by kfree(). 158 */ 159 void *memdup_user(const void __user *src, size_t len) 160 { 161 void *p; 162 163 p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN); 164 if (!p) 165 return ERR_PTR(-ENOMEM); 166 167 if (copy_from_user(p, src, len)) { 168 kfree(p); 169 return ERR_PTR(-EFAULT); 170 } 171 172 return p; 173 } 174 EXPORT_SYMBOL(memdup_user); 175 176 /** 177 * vmemdup_user - duplicate memory region from user space 178 * 179 * @src: source address in user space 180 * @len: number of bytes to copy 181 * 182 * Return: an ERR_PTR() on failure. Result may be not 183 * physically contiguous. Use kvfree() to free. 184 */ 185 void *vmemdup_user(const void __user *src, size_t len) 186 { 187 void *p; 188 189 p = kvmalloc(len, GFP_USER); 190 if (!p) 191 return ERR_PTR(-ENOMEM); 192 193 if (copy_from_user(p, src, len)) { 194 kvfree(p); 195 return ERR_PTR(-EFAULT); 196 } 197 198 return p; 199 } 200 EXPORT_SYMBOL(vmemdup_user); 201 202 /** 203 * strndup_user - duplicate an existing string from user space 204 * @s: The string to duplicate 205 * @n: Maximum number of bytes to copy, including the trailing NUL. 206 * 207 * Return: newly allocated copy of @s or an ERR_PTR() in case of error 208 */ 209 char *strndup_user(const char __user *s, long n) 210 { 211 char *p; 212 long length; 213 214 length = strnlen_user(s, n); 215 216 if (!length) 217 return ERR_PTR(-EFAULT); 218 219 if (length > n) 220 return ERR_PTR(-EINVAL); 221 222 p = memdup_user(s, length); 223 224 if (IS_ERR(p)) 225 return p; 226 227 p[length - 1] = '\0'; 228 229 return p; 230 } 231 EXPORT_SYMBOL(strndup_user); 232 233 /** 234 * memdup_user_nul - duplicate memory region from user space and NUL-terminate 235 * 236 * @src: source address in user space 237 * @len: number of bytes to copy 238 * 239 * Return: an ERR_PTR() on failure. 240 */ 241 void *memdup_user_nul(const void __user *src, size_t len) 242 { 243 char *p; 244 245 /* 246 * Always use GFP_KERNEL, since copy_from_user() can sleep and 247 * cause pagefault, which makes it pointless to use GFP_NOFS 248 * or GFP_ATOMIC. 249 */ 250 p = kmalloc_track_caller(len + 1, GFP_KERNEL); 251 if (!p) 252 return ERR_PTR(-ENOMEM); 253 254 if (copy_from_user(p, src, len)) { 255 kfree(p); 256 return ERR_PTR(-EFAULT); 257 } 258 p[len] = '\0'; 259 260 return p; 261 } 262 EXPORT_SYMBOL(memdup_user_nul); 263 264 void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma, 265 struct vm_area_struct *prev, struct rb_node *rb_parent) 266 { 267 struct vm_area_struct *next; 268 269 vma->vm_prev = prev; 270 if (prev) { 271 next = prev->vm_next; 272 prev->vm_next = vma; 273 } else { 274 mm->mmap = vma; 275 if (rb_parent) 276 next = rb_entry(rb_parent, 277 struct vm_area_struct, vm_rb); 278 else 279 next = NULL; 280 } 281 vma->vm_next = next; 282 if (next) 283 next->vm_prev = vma; 284 } 285 286 /* Check if the vma is being used as a stack by this task */ 287 int vma_is_stack_for_current(struct vm_area_struct *vma) 288 { 289 struct task_struct * __maybe_unused t = current; 290 291 return (vma->vm_start <= KSTK_ESP(t) && vma->vm_end >= KSTK_ESP(t)); 292 } 293 294 #if defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT) 295 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack) 296 { 297 mm->mmap_base = TASK_UNMAPPED_BASE; 298 mm->get_unmapped_area = arch_get_unmapped_area; 299 } 300 #endif 301 302 /* 303 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall 304 * back to the regular GUP. 305 * Note a difference with get_user_pages_fast: this always returns the 306 * number of pages pinned, 0 if no pages were pinned. 307 * If the architecture does not support this function, simply return with no 308 * pages pinned. 309 */ 310 int __weak __get_user_pages_fast(unsigned long start, 311 int nr_pages, int write, struct page **pages) 312 { 313 return 0; 314 } 315 EXPORT_SYMBOL_GPL(__get_user_pages_fast); 316 317 /** 318 * get_user_pages_fast() - pin user pages in memory 319 * @start: starting user address 320 * @nr_pages: number of pages from start to pin 321 * @gup_flags: flags modifying pin behaviour 322 * @pages: array that receives pointers to the pages pinned. 323 * Should be at least nr_pages long. 324 * 325 * get_user_pages_fast provides equivalent functionality to get_user_pages, 326 * operating on current and current->mm, with force=0 and vma=NULL. However 327 * unlike get_user_pages, it must be called without mmap_sem held. 328 * 329 * get_user_pages_fast may take mmap_sem and page table locks, so no 330 * assumptions can be made about lack of locking. get_user_pages_fast is to be 331 * implemented in a way that is advantageous (vs get_user_pages()) when the 332 * user memory area is already faulted in and present in ptes. However if the 333 * pages have to be faulted in, it may turn out to be slightly slower so 334 * callers need to carefully consider what to use. On many architectures, 335 * get_user_pages_fast simply falls back to get_user_pages. 336 * 337 * Return: number of pages pinned. This may be fewer than the number 338 * requested. If nr_pages is 0 or negative, returns 0. If no pages 339 * were pinned, returns -errno. 340 */ 341 int __weak get_user_pages_fast(unsigned long start, 342 int nr_pages, unsigned int gup_flags, 343 struct page **pages) 344 { 345 return get_user_pages_unlocked(start, nr_pages, pages, gup_flags); 346 } 347 EXPORT_SYMBOL_GPL(get_user_pages_fast); 348 349 unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr, 350 unsigned long len, unsigned long prot, 351 unsigned long flag, unsigned long pgoff) 352 { 353 unsigned long ret; 354 struct mm_struct *mm = current->mm; 355 unsigned long populate; 356 LIST_HEAD(uf); 357 358 ret = security_mmap_file(file, prot, flag); 359 if (!ret) { 360 if (down_write_killable(&mm->mmap_sem)) 361 return -EINTR; 362 ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff, 363 &populate, &uf); 364 up_write(&mm->mmap_sem); 365 userfaultfd_unmap_complete(mm, &uf); 366 if (populate) 367 mm_populate(ret, populate); 368 } 369 return ret; 370 } 371 372 unsigned long vm_mmap(struct file *file, unsigned long addr, 373 unsigned long len, unsigned long prot, 374 unsigned long flag, unsigned long offset) 375 { 376 if (unlikely(offset + PAGE_ALIGN(len) < offset)) 377 return -EINVAL; 378 if (unlikely(offset_in_page(offset))) 379 return -EINVAL; 380 381 return vm_mmap_pgoff(file, addr, len, prot, flag, offset >> PAGE_SHIFT); 382 } 383 EXPORT_SYMBOL(vm_mmap); 384 385 /** 386 * kvmalloc_node - attempt to allocate physically contiguous memory, but upon 387 * failure, fall back to non-contiguous (vmalloc) allocation. 388 * @size: size of the request. 389 * @flags: gfp mask for the allocation - must be compatible (superset) with GFP_KERNEL. 390 * @node: numa node to allocate from 391 * 392 * Uses kmalloc to get the memory but if the allocation fails then falls back 393 * to the vmalloc allocator. Use kvfree for freeing the memory. 394 * 395 * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported. 396 * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is 397 * preferable to the vmalloc fallback, due to visible performance drawbacks. 398 * 399 * Please note that any use of gfp flags outside of GFP_KERNEL is careful to not 400 * fall back to vmalloc. 401 * 402 * Return: pointer to the allocated memory of %NULL in case of failure 403 */ 404 void *kvmalloc_node(size_t size, gfp_t flags, int node) 405 { 406 gfp_t kmalloc_flags = flags; 407 void *ret; 408 409 /* 410 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables) 411 * so the given set of flags has to be compatible. 412 */ 413 if ((flags & GFP_KERNEL) != GFP_KERNEL) 414 return kmalloc_node(size, flags, node); 415 416 /* 417 * We want to attempt a large physically contiguous block first because 418 * it is less likely to fragment multiple larger blocks and therefore 419 * contribute to a long term fragmentation less than vmalloc fallback. 420 * However make sure that larger requests are not too disruptive - no 421 * OOM killer and no allocation failure warnings as we have a fallback. 422 */ 423 if (size > PAGE_SIZE) { 424 kmalloc_flags |= __GFP_NOWARN; 425 426 if (!(kmalloc_flags & __GFP_RETRY_MAYFAIL)) 427 kmalloc_flags |= __GFP_NORETRY; 428 } 429 430 ret = kmalloc_node(size, kmalloc_flags, node); 431 432 /* 433 * It doesn't really make sense to fallback to vmalloc for sub page 434 * requests 435 */ 436 if (ret || size <= PAGE_SIZE) 437 return ret; 438 439 return __vmalloc_node_flags_caller(size, node, flags, 440 __builtin_return_address(0)); 441 } 442 EXPORT_SYMBOL(kvmalloc_node); 443 444 /** 445 * kvfree() - Free memory. 446 * @addr: Pointer to allocated memory. 447 * 448 * kvfree frees memory allocated by any of vmalloc(), kmalloc() or kvmalloc(). 449 * It is slightly more efficient to use kfree() or vfree() if you are certain 450 * that you know which one to use. 451 * 452 * Context: Either preemptible task context or not-NMI interrupt. 453 */ 454 void kvfree(const void *addr) 455 { 456 if (is_vmalloc_addr(addr)) 457 vfree(addr); 458 else 459 kfree(addr); 460 } 461 EXPORT_SYMBOL(kvfree); 462 463 static inline void *__page_rmapping(struct page *page) 464 { 465 unsigned long mapping; 466 467 mapping = (unsigned long)page->mapping; 468 mapping &= ~PAGE_MAPPING_FLAGS; 469 470 return (void *)mapping; 471 } 472 473 /* Neutral page->mapping pointer to address_space or anon_vma or other */ 474 void *page_rmapping(struct page *page) 475 { 476 page = compound_head(page); 477 return __page_rmapping(page); 478 } 479 480 /* 481 * Return true if this page is mapped into pagetables. 482 * For compound page it returns true if any subpage of compound page is mapped. 483 */ 484 bool page_mapped(struct page *page) 485 { 486 int i; 487 488 if (likely(!PageCompound(page))) 489 return atomic_read(&page->_mapcount) >= 0; 490 page = compound_head(page); 491 if (atomic_read(compound_mapcount_ptr(page)) >= 0) 492 return true; 493 if (PageHuge(page)) 494 return false; 495 for (i = 0; i < (1 << compound_order(page)); i++) { 496 if (atomic_read(&page[i]._mapcount) >= 0) 497 return true; 498 } 499 return false; 500 } 501 EXPORT_SYMBOL(page_mapped); 502 503 struct anon_vma *page_anon_vma(struct page *page) 504 { 505 unsigned long mapping; 506 507 page = compound_head(page); 508 mapping = (unsigned long)page->mapping; 509 if ((mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) 510 return NULL; 511 return __page_rmapping(page); 512 } 513 514 struct address_space *page_mapping(struct page *page) 515 { 516 struct address_space *mapping; 517 518 page = compound_head(page); 519 520 /* This happens if someone calls flush_dcache_page on slab page */ 521 if (unlikely(PageSlab(page))) 522 return NULL; 523 524 if (unlikely(PageSwapCache(page))) { 525 swp_entry_t entry; 526 527 entry.val = page_private(page); 528 return swap_address_space(entry); 529 } 530 531 mapping = page->mapping; 532 if ((unsigned long)mapping & PAGE_MAPPING_ANON) 533 return NULL; 534 535 return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS); 536 } 537 EXPORT_SYMBOL(page_mapping); 538 539 /* 540 * For file cache pages, return the address_space, otherwise return NULL 541 */ 542 struct address_space *page_mapping_file(struct page *page) 543 { 544 if (unlikely(PageSwapCache(page))) 545 return NULL; 546 return page_mapping(page); 547 } 548 549 /* Slow path of page_mapcount() for compound pages */ 550 int __page_mapcount(struct page *page) 551 { 552 int ret; 553 554 ret = atomic_read(&page->_mapcount) + 1; 555 /* 556 * For file THP page->_mapcount contains total number of mapping 557 * of the page: no need to look into compound_mapcount. 558 */ 559 if (!PageAnon(page) && !PageHuge(page)) 560 return ret; 561 page = compound_head(page); 562 ret += atomic_read(compound_mapcount_ptr(page)) + 1; 563 if (PageDoubleMap(page)) 564 ret--; 565 return ret; 566 } 567 EXPORT_SYMBOL_GPL(__page_mapcount); 568 569 int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS; 570 int sysctl_overcommit_ratio __read_mostly = 50; 571 unsigned long sysctl_overcommit_kbytes __read_mostly; 572 int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT; 573 unsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL << 17; /* 128MB */ 574 unsigned long sysctl_admin_reserve_kbytes __read_mostly = 1UL << 13; /* 8MB */ 575 576 int overcommit_ratio_handler(struct ctl_table *table, int write, 577 void __user *buffer, size_t *lenp, 578 loff_t *ppos) 579 { 580 int ret; 581 582 ret = proc_dointvec(table, write, buffer, lenp, ppos); 583 if (ret == 0 && write) 584 sysctl_overcommit_kbytes = 0; 585 return ret; 586 } 587 588 int overcommit_kbytes_handler(struct ctl_table *table, int write, 589 void __user *buffer, size_t *lenp, 590 loff_t *ppos) 591 { 592 int ret; 593 594 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 595 if (ret == 0 && write) 596 sysctl_overcommit_ratio = 0; 597 return ret; 598 } 599 600 /* 601 * Committed memory limit enforced when OVERCOMMIT_NEVER policy is used 602 */ 603 unsigned long vm_commit_limit(void) 604 { 605 unsigned long allowed; 606 607 if (sysctl_overcommit_kbytes) 608 allowed = sysctl_overcommit_kbytes >> (PAGE_SHIFT - 10); 609 else 610 allowed = ((totalram_pages() - hugetlb_total_pages()) 611 * sysctl_overcommit_ratio / 100); 612 allowed += total_swap_pages; 613 614 return allowed; 615 } 616 617 /* 618 * Make sure vm_committed_as in one cacheline and not cacheline shared with 619 * other variables. It can be updated by several CPUs frequently. 620 */ 621 struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp; 622 623 /* 624 * The global memory commitment made in the system can be a metric 625 * that can be used to drive ballooning decisions when Linux is hosted 626 * as a guest. On Hyper-V, the host implements a policy engine for dynamically 627 * balancing memory across competing virtual machines that are hosted. 628 * Several metrics drive this policy engine including the guest reported 629 * memory commitment. 630 */ 631 unsigned long vm_memory_committed(void) 632 { 633 return percpu_counter_read_positive(&vm_committed_as); 634 } 635 EXPORT_SYMBOL_GPL(vm_memory_committed); 636 637 /* 638 * Check that a process has enough memory to allocate a new virtual 639 * mapping. 0 means there is enough memory for the allocation to 640 * succeed and -ENOMEM implies there is not. 641 * 642 * We currently support three overcommit policies, which are set via the 643 * vm.overcommit_memory sysctl. See Documentation/vm/overcommit-accounting.rst 644 * 645 * Strict overcommit modes added 2002 Feb 26 by Alan Cox. 646 * Additional code 2002 Jul 20 by Robert Love. 647 * 648 * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise. 649 * 650 * Note this is a helper function intended to be used by LSMs which 651 * wish to use this logic. 652 */ 653 int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) 654 { 655 long allowed; 656 657 VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) < 658 -(s64)vm_committed_as_batch * num_online_cpus(), 659 "memory commitment underflow"); 660 661 vm_acct_memory(pages); 662 663 /* 664 * Sometimes we want to use more memory than we have 665 */ 666 if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS) 667 return 0; 668 669 if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) { 670 if (pages > totalram_pages() + total_swap_pages) 671 goto error; 672 return 0; 673 } 674 675 allowed = vm_commit_limit(); 676 /* 677 * Reserve some for root 678 */ 679 if (!cap_sys_admin) 680 allowed -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10); 681 682 /* 683 * Don't let a single process grow so big a user can't recover 684 */ 685 if (mm) { 686 long reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10); 687 688 allowed -= min_t(long, mm->total_vm / 32, reserve); 689 } 690 691 if (percpu_counter_read_positive(&vm_committed_as) < allowed) 692 return 0; 693 error: 694 vm_unacct_memory(pages); 695 696 return -ENOMEM; 697 } 698 699 /** 700 * get_cmdline() - copy the cmdline value to a buffer. 701 * @task: the task whose cmdline value to copy. 702 * @buffer: the buffer to copy to. 703 * @buflen: the length of the buffer. Larger cmdline values are truncated 704 * to this length. 705 * 706 * Return: the size of the cmdline field copied. Note that the copy does 707 * not guarantee an ending NULL byte. 708 */ 709 int get_cmdline(struct task_struct *task, char *buffer, int buflen) 710 { 711 int res = 0; 712 unsigned int len; 713 struct mm_struct *mm = get_task_mm(task); 714 unsigned long arg_start, arg_end, env_start, env_end; 715 if (!mm) 716 goto out; 717 if (!mm->arg_end) 718 goto out_mm; /* Shh! No looking before we're done */ 719 720 down_read(&mm->mmap_sem); 721 arg_start = mm->arg_start; 722 arg_end = mm->arg_end; 723 env_start = mm->env_start; 724 env_end = mm->env_end; 725 up_read(&mm->mmap_sem); 726 727 len = arg_end - arg_start; 728 729 if (len > buflen) 730 len = buflen; 731 732 res = access_process_vm(task, arg_start, buffer, len, FOLL_FORCE); 733 734 /* 735 * If the nul at the end of args has been overwritten, then 736 * assume application is using setproctitle(3). 737 */ 738 if (res > 0 && buffer[res-1] != '\0' && len < buflen) { 739 len = strnlen(buffer, res); 740 if (len < res) { 741 res = len; 742 } else { 743 len = env_end - env_start; 744 if (len > buflen - res) 745 len = buflen - res; 746 res += access_process_vm(task, env_start, 747 buffer+res, len, 748 FOLL_FORCE); 749 res = strnlen(buffer, res); 750 } 751 } 752 out_mm: 753 mmput(mm); 754 out: 755 return res; 756 } 757