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Subject[PATCH v1] iov_iter: fix page_copy_sane for compound pages
Date
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>
---
lib/iov_iter.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 52c8dd6d8e82..1c1c06ddc20a 100644
--- 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;
--
2.14.1.342.g6490525c54-goog
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