From: Eric Dumazet <edumazet@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/pagemap.h | 24 +++++++++---------------
1 file changed, 9 insertions(+), 15 deletions(-)
diff -puN include/linux/pagemap.h~mm-tighten-fault_in_pages_writeable include/linux/pagemap.h
--- a/include/linux/pagemap.h~mm-tighten-fault_in_pages_writeable
+++ a/include/linux/pagemap.h
@@ -518,33 +518,27 @@ void page_endio(struct page *page, int r
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;
}
_
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