[PATCH 5.13 096/104] SMB3: fix readpage for large swap cache

[Greg Kroah-Hartman]

From: Steve French <stfrench@xxxxxxxxxxxxx>

commit f2a26a3cff27dfa456fef386fe5df56dcb4b47b6 upstream.

readpage was calculating the offset of the page incorrectly
for the case of large swapcaches.

    loff_t offset = (loff_t)page->index << PAGE_SHIFT;

As pointed out by Matthew Wilcox, this needs to use
page_file_offset() to calculate the offset instead.
Pages coming from the swap cache have page->index set
to their index within the swapcache, not within the backing
file.  For a sufficiently large swapcache, we could have
overlapping values of page->index within the same backing file.

Suggested by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.7+
Reviewed-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/cifs/file.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -4631,7 +4631,7 @@ read_complete:
 
 static int cifs_readpage(struct file *file, struct page *page)
 {
-	loff_t offset = (loff_t)page->index << PAGE_SHIFT;
+	loff_t offset = page_file_offset(page);
 	int rc = -EACCES;
 	unsigned int xid;