cifs: Fix signature miscalculation

[ Upstream commit 5a20b7c ]

Fix the calculation of packet signatures by adding the offset into a page
in the read or write data payload when hashing the pages from it.

Fixes: 39bc582 ("cifs: Add a function to Hash the contents of an iterator")
Signed-off-by: David Howells <[email protected]>
Reviewed-by: Tom Talpey <[email protected]>
Reviewed-by: Paulo Alcantara (Red Hat) <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: Jeff Layton <[email protected]>
cc: [email protected]
cc: [email protected]
Signed-off-by: Steve French <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

fs/smb/client/cifsencrypt.c

@@ -129,7 +129,7 @@ static ssize_t cifs_shash_xarray(const struct iov_iter *iter, ssize_t maxsize,
 			for (j = foffset / PAGE_SIZE; j < npages; j++) {
 				len = min_t(size_t, maxsize, PAGE_SIZE - offset);
 				p = kmap_local_page(folio_page(folio, j));
-				ret = crypto_shash_update(shash, p, len);
+				ret = crypto_shash_update(shash, p + offset, len);
 				kunmap_local(p);
 				if (ret < 0)
 					return ret;