Move __cleanup into mprotect'ed page to prevent unintentional modifications

similar to the atexit handlers. Idea and help deraadt@, ok deraadt@

5 files changed, 90 insertions, 27 deletions

diff --git a/src/lib/libc/stdlib/abort.c b/src/lib/libc/stdlib/abort.c
index 41a9f0f48b..7057f9b1ad 100644
--- a/src/lib/libc/stdlib/abort.c
+++ b/src/lib/libc/stdlib/abort.c
@@ -32,19 +32,19 @@
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char *rcsid = "$OpenBSD: abort.c,v 1.7 2001/08/12 12:03:01 heko Exp $";
+static char *rcsid = "$OpenBSD: abort.c,v 1.8 2002/09/14 22:03:14 dhartmei Exp $";
 #endif /* LIBC_SCCS and not lint */
 
 #include <signal.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include "thread_private.h"
-
-void (*__cleanup)();
+#include "atexit.h"
 
 void
 abort()
 {
+        struct atexit *p = __atexit;
         static int cleanup_called = 0;
         sigset_t mask;
 
@@ -64,9 +64,13 @@ abort()
         /*
          * POSIX requires we flush stdio buffers on abort
          */
-        if (cleanup_called == 0 && __cleanup != NULL) {
-                cleanup_called = 1;
-                (*__cleanup)();
+        if (cleanup_called == 0) {
+                while (p != NULL && p->next != NULL)
+                        p = p->next;
+                if (p != NULL && p->fns[0] != NULL) {
+                        cleanup_called = 1;
+                        (*p->fns[0])();
+                }
         }
 
         (void)kill(getpid(), SIGABRT);
diff --git a/src/lib/libc/stdlib/atexit.c b/src/lib/libc/stdlib/atexit.c
index da5a0ddda0..98564d0dd3 100644
--- a/src/lib/libc/stdlib/atexit.c
+++ b/src/lib/libc/stdlib/atexit.c
@@ -29,7 +29,7 @@
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char *rcsid = "$OpenBSD: atexit.c,v 1.6 2002/09/06 22:48:34 henning Exp $";
+static char *rcsid = "$OpenBSD: atexit.c,v 1.7 2002/09/14 22:03:14 dhartmei Exp $";
 #endif /* LIBC_SCCS and not lint */
 
 #include <sys/types.h>
@@ -42,6 +42,20 @@ int __atexit_invalid = 1;
 struct atexit *__atexit;
 
 /*
+ * Function pointers are stored in a linked list of pages. The list
+ * is initially empty, and pages are allocated on demand. The first
+ * function pointer in the first allocated page (the last one in
+ * the linked list) is reserved for the cleanup function.
+ *
+ * Outside the following two functions, all pages are mprotect()'ed
+ * to prevent unintentional/malicious corruption.
+ *
+ * The free(malloc(1)) is a workaround causing malloc_init() to
+ * ensure that malloc.c gets the first mmap() call for its sbrk()
+ * games.
+ */
+
+/*
  * Register a function to be performed at exit.
  */
 int
@@ -61,9 +75,6 @@ atexit(fn)
         }
         if (p == NULL) {
                 if (__atexit_invalid) {
-                        /* malloc.c wants the first mmap() for sbrk()
-                           games ('nice hack'), so enforce
-                           malloc_init() with a dummy call.  */
                         free(malloc(1));
                         __atexit_invalid = 0;
                 }
@@ -71,7 +82,11 @@ atexit(fn)
                     MAP_ANON | MAP_PRIVATE, -1, 0);
                 if (p == MAP_FAILED)
                         return (-1);
-                p->ind = 0;
+                if (__atexit == NULL) {
+                        p->fns[0] = NULL;
+                        p->ind = 1;
+                } else
+                        p->ind = 0;
                 p->max = (pgsize - ((char *)&p->fns[0] - (char *)p)) /
                     sizeof(p->fns[0]);
                 p->next = __atexit;
@@ -82,3 +97,39 @@ atexit(fn)
                 return (-1);
         return (0);
 }
+
+/*
+ * Register the cleanup function
+ */
+void
+__atexit_register_cleanup(fn)
+        void (*fn)();
+{
+        register struct atexit *p = __atexit;
+        register int pgsize = getpagesize();
+
+        if (pgsize < sizeof(*p))
+                return;
+        while (p != NULL && p->next != NULL)
+                p = p->next;
+        if (p == NULL) {
+                if (__atexit_invalid) {
+                        free(malloc(1));
+                        __atexit_invalid = 0;
+                }
+                p = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
+                    MAP_ANON | MAP_PRIVATE, -1, 0);
+                if (p == MAP_FAILED)
+                        return;
+                p->ind = 1;
+                p->max = (pgsize - ((char *)&p->fns[0] - (char *)p)) /
+                    sizeof(p->fns[0]);
+                p->next = NULL;
+                __atexit = p;
+        } else {
+                if (mprotect(p, pgsize, PROT_READ | PROT_WRITE))
+                    return;
+        }
+        p->fns[0] = fn;
+        mprotect(p, pgsize, PROT_READ);
+}
diff --git a/src/lib/libc/stdlib/exit.c b/src/lib/libc/stdlib/exit.c
index c69639125e..e22bd5178e 100644
--- a/src/lib/libc/stdlib/exit.c
+++ b/src/lib/libc/stdlib/exit.c
@@ -32,7 +32,7 @@
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char *rcsid = "$OpenBSD: exit.c,v 1.7 2002/08/30 07:58:07 dhartmei Exp $";
+static char *rcsid = "$OpenBSD: exit.c,v 1.8 2002/09/14 22:03:14 dhartmei Exp $";
 #endif /* LIBC_SCCS and not lint */
 
 #include <sys/types.h>
@@ -42,8 +42,6 @@ static char *rcsid = "$OpenBSD: exit.c,v 1.7 2002/08/30 07:58:07 dhartmei Exp $"
 #include "atexit.h"
 #include "thread_private.h"
 
-void (*__cleanup)();
-
 /*
  * This variable is zero until a process has created a thread.
  * It is used to avoid calling locking functions in libc when they
@@ -67,13 +65,13 @@ exit(status)
                 p = __atexit;
                 while (p != NULL) {
                         for (n = p->ind; --n >= 0;)
-                                (*p->fns[n])();
+                                if (p->fns[n] != NULL)
+                                        (*p->fns[n])();
                         q = p;
                         p = p->next;
                         munmap(q, pgsize);
                 }
         }
-        if (__cleanup)
-                (*__cleanup)();
+        /* cleanup, if registered, was called through fns[0] in the last page */
         _exit(status);
 }
diff --git a/src/regress/lib/libc/atexit/Makefile b/src/regress/lib/libc/atexit/Makefile
index 89625e2a7b..55c3f3981e 100644
--- a/src/regress/lib/libc/atexit/Makefile
+++ b/src/regress/lib/libc/atexit/Makefile
@@ -1,4 +1,4 @@
-#       $OpenBSD: Makefile,v 1.2 2002/09/02 19:59:51 avsm Exp $
+#       $OpenBSD: Makefile,v 1.3 2002/09/14 22:03:14 dhartmei Exp $
 
 NOMAN=
 PROG=atexit_test
@@ -6,7 +6,9 @@ PROG=atexit_test
 run-regress-atexit_test: ${PROG}
         ./${PROG} -valid 2>${.OBJDIR}/valid.out
         cmp -s ${.OBJDIR}/valid.out ${.CURDIR}/valid.ok
-        ./${PROG} -invalid 2>${.OBJDIR}/invalid.out
+        ./${PROG} -invalid-atexit 2>${.OBJDIR}/invalid.out
+        cmp -s ${.OBJDIR}/invalid.out ${.CURDIR}/invalid.ok
+        ./${PROG} -invalid-cleanup 2>${.OBJDIR}/invalid.out
         cmp -s ${.OBJDIR}/invalid.out ${.CURDIR}/invalid.ok
 
 .include <bsd.regress.mk>
diff --git a/src/regress/lib/libc/atexit/atexit_test.c b/src/regress/lib/libc/atexit/atexit_test.c
index fcfe95cb02..fea95832ab 100644
--- a/src/regress/lib/libc/atexit/atexit_test.c
+++ b/src/regress/lib/libc/atexit/atexit_test.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: atexit_test.c,v 1.1 2002/07/29 19:51:41 dhartmei Exp $ */
+/*      $OpenBSD: atexit_test.c,v 1.2 2002/09/14 22:03:14 dhartmei Exp $ */
 
 /*
  * Copyright (c) 2002 Daniel Hartmeier
@@ -39,9 +39,6 @@
 #include <signal.h>
 #include "/usr/src/lib/libc/stdlib/atexit.h"
 
-extern struct atexit *__atexit;
-extern void (*__cleanup)();
-
 void    handle_first();
 void    handle_middle();
 void    handle_last();
@@ -57,8 +54,10 @@ main(int argc, char *argv[])
         int i;
 
         if (argc != 2 || (strcmp(argv[1], "-valid") &&
-            strcmp(argv[1], "-invalid"))) {
-                fprintf(stderr, "%s -valid/-invalid\n", argv[0]);
+            strcmp(argv[1], "-invalid-atexit") &&
+            strcmp(argv[1], "-invalid-cleanup"))) {
+                fprintf(stderr, "%s -valid/-invalid-atexit/-invalid-cleanup\n",
+                    argv[0]);
                 return (1);
         }
         fprintf(stderr, "main()\n");
@@ -77,11 +76,20 @@ main(int argc, char *argv[])
                 return (1);
         }
         /* this is supposed to segfault */
-        if (strcmp(argv[1], "-valid")) {
+        if (!strcmp(argv[1], "-invalid-atexit")) {
                 signal(SIGSEGV, handle_signal);
                 __atexit->fns[0] = handle_invalid;
+        } else if (!strcmp(argv[1], "-invalid-cleanup")) {
+                struct atexit *p = __atexit;
+
+                signal(SIGSEGV, handle_signal);
+                while (p != NULL && p->next != NULL)
+                        p = p->next;
+                if (p == NULL)
+                        fprintf(stderr, "p == NULL, no page found\n");
+                p->fns[0] = handle_invalid;
         }
-        __cleanup = handle_cleanup;
+        __atexit_register_cleanup(handle_cleanup);
         counter = 0;
         fprintf(stderr, "main() returns\n");
         return (0);