diff --git a/src/lib9p/uid.c b/src/lib9p/uid.c
new file mode 100644
index 0000000..84b98bd
--- /dev/null
+++ b/src/lib9p/uid.c
@@ -0,0 +1,34 @@
+#include <u.h>
+#include <libc.h>
+#include <auth.h>
+#include <fcall.h>
+#include <thread.h>
+#include <9p.h>
+
+/*
+ * simplistic permission checking.  assume that
+ * each user is the leader of her own group.
+ */
+int
+hasperm(File *f, char *uid, int p)
+{
+	int m;
+
+	m = f->dir.mode & 7;	/* other */
+	if((p & m) == p)
+		return 1;
+
+	if(strcmp(f->dir.uid, uid) == 0) {
+		m |= (f->dir.mode>>6) & 7;
+		if((p & m) == p)
+			return 1;
+	}
+
+	if(strcmp(f->dir.gid, uid) == 0) {
+		m |= (f->dir.mode>>3) & 7;
+		if((p & m) == p)
+			return 1;
+	}
+
+	return 0;
+}