[PATCH AUTOSEL 5.4 033/330] iomap: Fix overflow in iomap_page_mkwrite

[Sasha Levin]

From: Andreas Gruenbacher <agruenba@xxxxxxxxxx>

[ Upstream commit add66fcbd3fbe5aa0dd4dddfa23e119c12989a27 ]

On architectures where loff_t is wider than pgoff_t, the expression
((page->index + 1) << PAGE_SHIFT) can overflow.  Rewrite to use the page
offset, which we already compute here anyway.

Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/iomap/buffered-io.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index e25901ae3ff44..a30ea7ecb790a 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1040,20 +1040,19 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
 
 	lock_page(page);
 	size = i_size_read(inode);
-	if ((page->mapping != inode->i_mapping) ||
-	    (page_offset(page) > size)) {
+	offset = page_offset(page);
+	if (page->mapping != inode->i_mapping || offset > size) {
 		/* We overload EFAULT to mean page got truncated */
 		ret = -EFAULT;
 		goto out_unlock;
 	}
 
 	/* page is wholly or partially inside EOF */
-	if (((page->index + 1) << PAGE_SHIFT) > size)
+	if (offset > size - PAGE_SIZE)
 		length = offset_in_page(size);
 	else
 		length = PAGE_SIZE;
 
-	offset = page_offset(page);
 	while (length > 0) {
 		ret = iomap_apply(inode, offset, length,
 				IOMAP_WRITE | IOMAP_FAULT, ops, page,
-- 
2.25.1