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.

3 files changed, 87 insertions, 71 deletions

diff --git a/src/lib/libc/stdlib/atexit.c b/src/lib/libc/stdlib/atexit.c
index c0fb624141..554253362f 100644
--- a/src/lib/libc/stdlib/atexit.c
+++ b/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);
 }
diff --git a/src/lib/libc/stdlib/atexit.h b/src/lib/libc/stdlib/atexit.h
index e41a7cb86c..6424dfdbbc 100644
--- a/src/lib/libc/stdlib/atexit.h
+++ b/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 */
diff --git a/src/lib/libc/stdlib/exit.c b/src/lib/libc/stdlib/exit.c
index ab53f9400b..c16b33bd30 100644
--- a/src/lib/libc/stdlib/exit.c
+++ b/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);