Replace atexit handler. mprotect() the pages so an attempt to modify the

function pointers from the outside will segfault. Idea, hints and feedback
from deraadt. ok deraadt.

src/lib/libc/stdlib/atexit.c

@@ -1,46 +1,43 @@
-/*-
- * Copyright (c) 1990 The Regents of the University of California.
+/*
+ * Copyright (c) 2002 Daniel Hartmeier
  * All rights reserved.
  *
- * This code is derived from software contributed to Berkeley by
- * Chris Torek.
- *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *	This product includes software developed by the University of
- *	California, Berkeley and its contributors.
- * 4. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
  *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
+ *    - Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *    - Redistributions in binary form must reproduce the above
+ *      copyright notice, this list of conditions and the following
+ *      disclaimer in the documentation and/or other materials provided
+ *      with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char *rcsid = "$OpenBSD: atexit.c,v 1.2 1996/08/19 08:33:22 tholo Exp $";
+static char *rcsid = "$OpenBSD: atexit.c,v 1.3 2002/07/29 19:54:42 dhartmei Exp $";
 #endif /* LIBC_SCCS and not lint */
 
+#include <sys/types.h>
+#include <sys/mman.h>
 #include <stdlib.h>
 #include "atexit.h"
 
+int __atexit_invalid = 1;
 struct atexit *__atexit;
 
 /*
@@ -50,18 +47,32 @@ int
 atexit(fn)
 	void (*fn)();
 {
-	static struct atexit __atexit0;	/* one guaranteed table */
-	register struct atexit *p;
+	register struct atexit *p = __atexit;
+	register int pgsize = getpagesize();
 
-	if ((p = __atexit) == NULL)
-		__atexit = p = &__atexit0;
-	else if (p->ind >= ATEXIT_SIZE) {
-		if ((p = malloc(sizeof(*p))) == NULL)
+	if (pgsize < sizeof(*p))
+		return (-1);
+	if (p != NULL) {
+		if (p->ind + 1 >= p->max)
+			p = NULL;
+		else if (mprotect(p, pgsize, PROT_READ | PROT_WRITE))
+			return (-1);
+	}
+	if (p == NULL) {
+		p = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
+		    MAP_ANON | MAP_PRIVATE, -1, 0);
+		if (p == MAP_FAILED)
 			return (-1);
 		p->ind = 0;
+		p->max = (pgsize - ((char *)&p->fns[0] - (char *)p)) /
+		    sizeof(p->fns[0]);
 		p->next = __atexit;
 		__atexit = p;
+		if (__atexit_invalid)
+			__atexit_invalid = 0;
 	}
 	p->fns[p->ind++] = fn;
+	if (mprotect(p, pgsize, PROT_READ))
+		return (-1);
 	return (0);
 }

src/lib/libc/stdlib/atexit.h

@@ -1,45 +1,41 @@
-/*-
- * Copyright (c) 1990 The Regents of the University of California.
+/*	$OpenBSD: atexit.h,v 1.3 2002/07/29 19:54:42 dhartmei Exp $ */
+
+/*
+ * Copyright (c) 2002 Daniel Hartmeier
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *	This product includes software developed by the University of
- *	California, Berkeley and its contributors.
- * 4. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
  *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
+ *    - Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *    - Redistributions in binary form must reproduce the above
+ *      copyright notice, this list of conditions and the following
+ *      disclaimer in the documentation and/or other materials provided
+ *      with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
  *
- *	$OpenBSD: atexit.h,v 1.2 1996/08/19 08:33:23 tholo Exp $
  */
 
-/* must be at least 32 to guarantee ANSI conformance */
-#define	ATEXIT_SIZE	32
-
 struct atexit {
 	struct atexit *next;		/* next in list */
 	int ind;			/* next index in this table */
-	void (*fns[ATEXIT_SIZE])();	/* the table itself */
+	int max;			/* max entries >= ATEXIT_SIZE */
+	void (*fns[1])();		/* the table itself */
 };
 
+extern int __atexit_invalid;
 extern struct atexit *__atexit;		/* points to head of LIFO stack */

src/lib/libc/stdlib/exit.c

@@ -32,9 +32,11 @@
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char *rcsid = "$OpenBSD: exit.c,v 1.4 2000/01/06 08:45:50 d Exp $";
+static char *rcsid = "$OpenBSD: exit.c,v 1.5 2002/07/29 19:54:42 dhartmei Exp $";
 #endif /* LIBC_SCCS and not lint */
 
+#include <sys/types.h>
+#include <sys/mman.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include "atexit.h"
@@ -58,12 +60,19 @@ void
 exit(status)
 	int status;
 {
-	register struct atexit *p;
-	register int n;
+	register struct atexit *p, *q;
+	register int n, pgsize = getpagesize();
 
-	for (p = __atexit; p; p = p->next)
-		for (n = p->ind; --n >= 0;)
-			(*p->fns[n])();
+	if (!__atexit_invalid) {
+		p = __atexit;
+		while (p != NULL) {
+			for (n = p->ind; --n >= 0;)
+				(*p->fns[n])();
+			q = p;
+			p = p->next;
+			munmap(q, pgsize);
+		}
+	}
 	if (__cleanup)
 		(*__cleanup)();
 	_exit(status);