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 */
28void kfree_const(const void *x)
29{
30 if (!is_kernel_rodata((unsigned long)x))
31 kfree(x);
32}
33EXPORT_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 */
42char *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}
56EXPORT_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 */
68const 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}
75EXPORT_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 */
87char *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}
103EXPORT_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 */
114void *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}
123EXPORT_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 */
134char *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}
148EXPORT_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 */
159void *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}
174EXPORT_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 */
185void *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}
200EXPORT_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 %NULL in case of error
208 */
209char *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}
231EXPORT_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 */
241void *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}
262EXPORT_SYMBOL(memdup_user_nul);
263
264void __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 */
287int 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)
295void 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 */
310int __weak __get_user_pages_fast(unsigned long start,
311 int nr_pages, int write, struct page **pages)
312{
313 return 0;
314}
315EXPORT_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 * @write: whether pages will be written to
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 */
341int __weak get_user_pages_fast(unsigned long start,
342 int nr_pages, int write, struct page **pages)
343{
344 return get_user_pages_unlocked(start, nr_pages, pages,
345 write ? FOLL_WRITE : 0);
346}
347EXPORT_SYMBOL_GPL(get_user_pages_fast);
348
349unsigned 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
372unsigned 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}
383EXPORT_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 */
404void *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}
442EXPORT_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 */
454void kvfree(const void *addr)
455{
456 if (is_vmalloc_addr(addr))
457 vfree(addr);
458 else
459 kfree(addr);
460}
461EXPORT_SYMBOL(kvfree);
462
463static 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 */
474void *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 */
484bool 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}
501EXPORT_SYMBOL(page_mapped);
502
503struct 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
514struct 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}
537EXPORT_SYMBOL(page_mapping);
538
539/*
540 * For file cache pages, return the address_space, otherwise return NULL
541 */
542struct 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 */
550int __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}
567EXPORT_SYMBOL_GPL(__page_mapcount);
568
569int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
570int sysctl_overcommit_ratio __read_mostly = 50;
571unsigned long sysctl_overcommit_kbytes __read_mostly;
572int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
573unsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL << 17; /* 128MB */
574unsigned long sysctl_admin_reserve_kbytes __read_mostly = 1UL << 13; /* 8MB */
575
576int 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
588int 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 */
603unsigned 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 */
621struct 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 */
631unsigned long vm_memory_committed(void)
632{
633 return percpu_counter_read_positive(&vm_committed_as);
634}
635EXPORT_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 */
653int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
654{
655 long free, allowed, reserve;
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 free = global_zone_page_state(NR_FREE_PAGES);
671 free += global_node_page_state(NR_FILE_PAGES);
672
673 /*
674 * shmem pages shouldn't be counted as free in this
675 * case, they can't be purged, only swapped out, and
676 * that won't affect the overall amount of available
677 * memory in the system.
678 */
679 free -= global_node_page_state(NR_SHMEM);
680
681 free += get_nr_swap_pages();
682
683 /*
684 * Any slabs which are created with the
685 * SLAB_RECLAIM_ACCOUNT flag claim to have contents
686 * which are reclaimable, under pressure. The dentry
687 * cache and most inode caches should fall into this
688 */
689 free += global_node_page_state(NR_SLAB_RECLAIMABLE);
690
691 /*
692 * Part of the kernel memory, which can be released
693 * under memory pressure.
694 */
695 free += global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE);
696
697 /*
698 * Leave reserved pages. The pages are not for anonymous pages.
699 */
700 if (free <= totalreserve_pages)
701 goto error;
702 else
703 free -= totalreserve_pages;
704
705 /*
706 * Reserve some for root
707 */
708 if (!cap_sys_admin)
709 free -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10);
710
711 if (free > pages)
712 return 0;
713
714 goto error;
715 }
716
717 allowed = vm_commit_limit();
718 /*
719 * Reserve some for root
720 */
721 if (!cap_sys_admin)
722 allowed -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10);
723
724 /*
725 * Don't let a single process grow so big a user can't recover
726 */
727 if (mm) {
728 reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10);
729 allowed -= min_t(long, mm->total_vm / 32, reserve);
730 }
731
732 if (percpu_counter_read_positive(&vm_committed_as) < allowed)
733 return 0;
734error:
735 vm_unacct_memory(pages);
736
737 return -ENOMEM;
738}
739
740/**
741 * get_cmdline() - copy the cmdline value to a buffer.
742 * @task: the task whose cmdline value to copy.
743 * @buffer: the buffer to copy to.
744 * @buflen: the length of the buffer. Larger cmdline values are truncated
745 * to this length.
746 *
747 * Return: the size of the cmdline field copied. Note that the copy does
748 * not guarantee an ending NULL byte.
749 */
750int get_cmdline(struct task_struct *task, char *buffer, int buflen)
751{
752 int res = 0;
753 unsigned int len;
754 struct mm_struct *mm = get_task_mm(task);
755 unsigned long arg_start, arg_end, env_start, env_end;
756 if (!mm)
757 goto out;
758 if (!mm->arg_end)
759 goto out_mm; /* Shh! No looking before we're done */
760
761 down_read(&mm->mmap_sem);
762 arg_start = mm->arg_start;
763 arg_end = mm->arg_end;
764 env_start = mm->env_start;
765 env_end = mm->env_end;
766 up_read(&mm->mmap_sem);
767
768 len = arg_end - arg_start;
769
770 if (len > buflen)
771 len = buflen;
772
773 res = access_process_vm(task, arg_start, buffer, len, FOLL_FORCE);
774
775 /*
776 * If the nul at the end of args has been overwritten, then
777 * assume application is using setproctitle(3).
778 */
779 if (res > 0 && buffer[res-1] != '\0' && len < buflen) {
780 len = strnlen(buffer, res);
781 if (len < res) {
782 res = len;
783 } else {
784 len = env_end - env_start;
785 if (len > buflen - res)
786 len = buflen - res;
787 res += access_process_vm(task, env_start,
788 buffer+res, len,
789 FOLL_FORCE);
790 res = strnlen(buffer, res);
791 }
792 }
793out_mm:
794 mmput(mm);
795out:
796 return res;
797}
798