smb: client: require stable pages for signed connections

When signing, cifs computes the SMB signature over the pagecache folios
in place and then hands those same folios to the socket.  If a buffered
write mutates a folio while a write subrequest is still in flight, the
signature no longer matches the data that follows it, the server rejects
the write with STATUS_ACCESS_DENIED (-EACCES), and the error is latched
in the mapping, so the next fsync()/fallocate() returns -EIO.

Mark the mapping for stable writes so netfs_perform_write() waits for
writeback to complete before modifying an in-flight folio.  This is
only needed when the connection is signed.

Fixes: 3ee1a1fc39 ("cifs: Cut over to using netfslib")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

fs/smb/client/inode.c

@@ -88,6 +88,8 @@ static void cifs_set_ops(struct inode *inode)
 		else
 			inode->i_data.a_ops = &cifs_addr_ops;
 		mapping_set_large_folios(inode->i_mapping);
+		if (tcon->ses->server->sign)
+			mapping_set_stable_writes(inode->i_mapping);
 		break;
 	case S_IFDIR:
 		if (IS_AUTOMOUNT(inode)) {