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mm: tighten fault_in_pages_writeable() 

copy_page_to_iter_iovec() is currently the only user of
fault_in_pages_writeable(), and it definitely can use fragments from
high order pages.

Make sure fault_in_pages_writeable() is only touching two adjacent pages
at most, as claimed.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Dumazet 2016-05-20 16:57:53 -07:00 committed by Linus Torvalds
parent 297880f4af
commit b8ca9e3a61
1 changed files with 9 additions and 15 deletions
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24
include/linux/pagemap.h
View File

@ -518,33 +518,27 @@ void page_endio(struct page *page, int rw, int err);
extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
/*
* Fault a userspace page into pagetables. Return non-zero on a fault.
*
* This assumes that two userspace pages are always sufficient.
* Fault one or two userspace pages into pagetables.
* Return -EINVAL if more than two pages would be needed.
* Return non-zero on a fault.
*/
static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
int span, ret;
if (unlikely(size == 0))
return 0;
span = offset_in_page(uaddr) + size;
if (span > 2 * PAGE_SIZE)
return -EINVAL;
/*
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
ret = __put_user(0, uaddr);
if (ret == 0) {
char __user *end = uaddr + size - 1;
/*
* If the page was already mapped, this will get a cache miss
* for sure, so try to avoid doing it.
*/
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK))
ret = __put_user(0, end);
}
if (ret == 0 && span > PAGE_SIZE)
ret = __put_user(0, uaddr + size - 1);
return ret;
}