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iov_iter: fix page_copy_sane for compound pages 

Issue is that if the data crosses a page boundary inside a compound
page, this check will incorrectly trigger a WARN_ON.

To fix this, compute the order using the head of the compound page and
adjust the offset to be relative to that head.

Fixes: 72e809ed81 ("iov_iter: sanity checks for copy to/from page
primitives")

Signed-off-by: Petar Penkov <ppenkov@google.com>
CC: Al Viro <viro@zeniv.linux.org.uk>
CC: Eric Dumazet <edumazet@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Petar Penkov 2017-08-29 11:20:32 -07:00 committed by Al Viro
parent 2bd6bf03f4
commit a90bcb86ae
1 changed files with 4 additions and 2 deletions
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6
lib/iov_iter.c
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@ -687,8 +687,10 @@ EXPORT_SYMBOL(_copy_from_iter_full_nocache);
static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
{
size_t v = n + offset;
if (likely(n <= v && v <= (PAGE_SIZE << compound_order(page))))
struct page *head = compound_head(page);
size_t v = n + offset + page_address(page) - page_address(head);
if (likely(n <= v && v <= (PAGE_SIZE << compound_order(head))))
return true;
WARN_ON(1);
return false;