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: 72e809ed81ed ("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>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 52c8dd6d8e8290fa8df614e0017542a600b9c536..1c1c06ddc20a8a961d7d9f73e43d65b695636d5d 100644 (file)
--- 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;