SMB3: fix readpage for large swap cache

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@infradead.org>
Cc: <stable@vger.kernel.org> # v5.7+
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index da057570bb93d6ff9ce99701bb47d92d32e656b6..f46904a4ead31a59d4a5a60dba624c0929c14884 100644 (file)
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -4550,7 +4550,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page,
 
 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;