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Re: Patch for esound-0.2.19
From: Kris Kennaway <kris () FREEBSD ORG>
Date: Sat, 23 Sep 2000 18:42:29 -0700

On Mon, 11 Sep 2000, Alon Oz wrote:

Here's a patch that fixes the vulnerability in the esound package
(0.2.19 and prior):


------- CUT HERE ------------------------

*** esd.c       Mon Sep 11 13:48:10 2000
--- esd.c.noperms       Mon Sep 11 13:48:41 2000
***************
*** 218,230 ****
        if (access(ESD_UNIX_SOCKET_DIR, R_OK | W_OK) == -1)
        {
          mkdir(ESD_UNIX_SOCKET_DIR,
!               S_IRUSR|S_IWUSR|S_IXUSR|
!               S_IRGRP|S_IWGRP|S_IXGRP|
!               S_IROTH|S_IWOTH|S_IXOTH);
          chmod(ESD_UNIX_SOCKET_DIR,
!               S_IRUSR|S_IWUSR|S_IXUSR|
!               S_IRGRP|S_IWGRP|S_IXGRP|
!               S_IROTH|S_IWOTH|S_IXOTH);
        }
        if (access(ESD_UNIX_SOCKET_NAME, R_OK | W_OK) == -1)
        {
--- 218,226 ----
        if (access(ESD_UNIX_SOCKET_DIR, R_OK | W_OK) == -1)
        {
          mkdir(ESD_UNIX_SOCKET_DIR,
!               S_IRUSR|S_IWUSR|S_IXUSR);
          chmod(ESD_UNIX_SOCKET_DIR,
!               S_IRUSR|S_IWUSR|S_IXUSR);
        }
        if (access(ESD_UNIX_SOCKET_NAME, R_OK | W_OK) == -1)
        {

This patch is insufficient. It doesn't fix the race condition between
testing existence of the directory and creating it, so the attacker can
create their own directory after the access() test, then a bit later when
we attempt to chmod the socket the same thing happens:

      chmod(ESD_UNIX_SOCKET_NAME,
            S_IRUSR|S_IWUSR|S_IXUSR|
            S_IRGRP|S_IWGRP|S_IXGRP|
            S_IROTH|S_IWOTH|S_IXOTH);

and we will happily make any file or directory (e.g. $HOME) owned by the
user world-read/write/executable if ESD_UNIX_SOCKET_NAME is actually a
symlink.

FreeBSD fixed this (it was the subject of advisory 00:45) by moving the
ESD_UNIX_SOCKET_DIR into the user's home directory as well as fixing the
permissions so the attacker can't do what is necessary to exploit the
races.

Patches:

--- esd.h.orig  Thu Jun 29 23:12:53 2000
+++ esd.h       Thu Jun 29 23:12:41 2000
@@ -7,8 +7,15 @@
 #endif

 /* path and name of the default EsounD domain socket */
+#if 0
 #define ESD_UNIX_SOCKET_DIR    "/tmp/.esd"
 #define ESD_UNIX_SOCKET_NAME   ESD_UNIX_SOCKET_DIR ## "/" ## "socket"
+#else
+char *esd_unix_socket_dir(void);
+char *esd_unix_socket_name(void);
+#define ESD_UNIX_SOCKET_DIR    esd_unix_socket_dir()
+#define ESD_UNIX_SOCKET_NAME   esd_unix_socket_name()
+#endif

 /* length of the audio buffer size */
 #define ESD_BUF_SIZE (4 * 1024)
--- esd.c.orig  Tue Apr  4 11:20:08 2000
+++ esd.c       Thu Jun 29 23:34:18 2000
@@ -219,12 +219,12 @@
        {       
          mkdir(ESD_UNIX_SOCKET_DIR,
                S_IRUSR|S_IWUSR|S_IXUSR|
-               S_IRGRP|S_IWGRP|S_IXGRP|
-               S_IROTH|S_IWOTH|S_IXOTH);
+               S_IRGRP|S_IXGRP|
+               S_IROTH|S_IXOTH);
          chmod(ESD_UNIX_SOCKET_DIR,
                S_IRUSR|S_IWUSR|S_IXUSR|
-               S_IRGRP|S_IWGRP|S_IXGRP|
-               S_IROTH|S_IWOTH|S_IXOTH);
+               S_IRGRP|S_IXGRP|
+               S_IROTH|S_IXOTH);
        }
       if (access(ESD_UNIX_SOCKET_NAME, R_OK | W_OK) == -1)
        {
@@ -317,9 +317,9 @@
       /* let anyone access esd's socket - but we have authentication so they */
       /* wont get far if they dont have the auth key */
       chmod(ESD_UNIX_SOCKET_NAME,
-           S_IRUSR|S_IWUSR|S_IXUSR|
-           S_IRGRP|S_IWGRP|S_IXGRP|
-           S_IROTH|S_IWOTH|S_IXOTH);
+           S_IRUSR|S_IWUSR|
+           S_IRGRP|
+           S_IROTH);
     }
     if (listen(socket_listen,16)<0)
     {

--- esdlib.c.orig       Thu Jun 29 23:31:04 2000
+++ esdlib.c    Thu Jun 29 23:31:21 2000
@@ -19,6 +19,8 @@
 #include <arpa/inet.h>
 #include <errno.h>
 #include <sys/wait.h>
+#include <pwd.h>
+#include <limits.h>

 #include <sys/un.h>

@@ -1421,4 +1423,34 @@
     */

     return close( esd );
+}
+
+char *
+esd_unix_socket_dir(void) {
+       static char *sockdir = NULL, sockdirbuf[PATH_MAX];
+       struct passwd *pw;
+
+       if (sockdir != NULL)
+               return (sockdir);
+       pw = getpwuid(getuid());
+       if (pw == NULL || pw->pw_dir == NULL) {
+               fprintf(stderr, "esd: could not find home directory\n");
+               exit(1);
+       }
+       snprintf(sockdirbuf, sizeof(sockdirbuf), "%s/.esd", pw->pw_dir);
+       endpwent();
+       sockdir = sockdirbuf;
+       return (sockdir);
+}
+
+char *
+esd_unix_socket_name(void) {
+       static char *sockname = NULL, socknamebuf[PATH_MAX];
+
+       if (sockname != NULL)
+               return (sockname);
+       snprintf(socknamebuf, sizeof(socknamebuf), "%s/socket",
+           esd_unix_socket_dir());
+       sockname = socknamebuf;
+       return (sockname);
 }

While we're there, the build process also uses an insecure tempfile on
non-FreeBSD platforms. Patch:

--- ltmain.sh.orig      Thu Jun 29 23:41:49 2000
+++ ltmain.sh   Thu Jun 29 23:45:36 2000
@@ -3227,7 +3227,7 @@
          outputname=
          if test "$fast_install" = no && test -n "$relink_command"; then
            if test "$finalize" = yes; then
-             outputname="/tmp/$$-$file"
+             outputname=$(mktemp "${TMPDIR:-/tmp}/$file.XXXXXX") || exit $?
              # Replace the output file specification.
              relink_command=`$echo "X$relink_command" | $Xsed -e 's% () OUTPUT@%'"$outputname"'%g'`

Kris

--
In God we Trust -- all others must submit an X.509 certificate.
    -- Charles Forsythe <forsythe () alum mit edu>


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