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: 72e809e ("iov_iter: sanity checks for copy to/from page primitives") Signed-off-by: Petar Penkov <[email protected]> CC: Al Viro <[email protected]> CC: Eric Dumazet <[email protected]> Signed-off-by: Al Viro <[email protected]>
josf · Sep 21, 2017 · a90bcb8 · a90bcb8
1 parent 2bd6bf0
commit a90bcb8
Showing 1 changed file with 4 additions and 2 deletions.
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
@@ -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;