p9_client_readdir() fix

Don't assume that server is sane and won't return more data than
asked for.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

net/9p/client.c

@@ -2101,6 +2101,10 @@ int p9_client_readdir(struct p9_fid *fid, char *data, u32 count, u64 offset)
 		trace_9p_protocol_dump(clnt, req->rc);
 		goto free_and_error;
 	}
+	if (rsize < count) {
+		pr_err("bogus RREADDIR count (%d > %d)\n", count, rsize);
+		count = rsize;
+	}
 
 	p9_debug(P9_DEBUG_9P, "<<< RREADDIR count %d\n", count);