* NEWS, libmisc/chowntty.c, libmisc/utmp.c: is_my_tty() moved from

	utmp.c to chowntty.c. checkutmp() now only uses an existing utmp
	entry if the pid matches and ut_line matches with the current tty.
	This fixes a possible DOS when entries can be forged in the utmp
	file.
	* libmisc/chowntty.c, src/login.c, lib/prototypes.h: Remove the
	tty argument from chown_tty. chown_tty always changes stdin and
	does not need this argument anymore.

diff --git a/ChangeLog b/ChangeLog
index 31d5597f0d6c4fea732e06d9394d594bd8660ba9..7c551c5cb019b5a00286fdc60e8e04c2edf220ea 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,14 @@
 
        * NEWS, libmisc/chowntty.c: Fix a race condition that could lead to
        gaining ownership or changing mode of arbitrary files.
+       * NEWS, libmisc/chowntty.c, libmisc/utmp.c: is_my_tty() moved from
+       utmp.c to chowntty.c. checkutmp() now only uses an existing utmp
+       entry if the pid matches and ut_line matches with the current tty.
+       This fixes a possible DOS when entries can be forged in the utmp
+       file.
+       * libmisc/chowntty.c, src/login.c, lib/prototypes.h: Remove the
+       tty argument from chown_tty. chown_tty always changes stdin and
+       does not need this argument anymore.
 
 2008-10-11  Nicolas François  <nicolas.francois@centraliens.net>
 

diff --git a/NEWS b/NEWS
index b91ec42e0ce1f280ed94b335a666e4aa3999dd32..7aab4d409f769ef895f9a37b86bd132f29502ef7 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -64,6 +64,8 @@ shadow-4.1.2.1 -> shadow-4.1.2.2                                      23-11-2008
 *** security
 - Fix a race condition in login that could lead to gaining ownership or
   changing mode of arbitrary files.
+- Fix a possible login DOS, which could be caused by injecting forged
+  entries in utmp.
 
 shadow-4.1.2 -> shadow-4.1.2.1                                         26-06-2008
 

diff --git a/libmisc/chowntty.c b/libmisc/chowntty.c
index 4a4d0aeba9f7794d8d9c5940b90bfe4eb8cbf9fa..89ebb0e816260423eac81302ffe22b3a30f60298 100644 (file)
--- a/libmisc/chowntty.c
+++ b/libmisc/chowntty.c
@@ -43,32 +43,14 @@
 #include "defines.h"
 #include <pwd.h>
 #include "getdef.h"
-/*
- * is_my_tty -- determine if "tty" is the same as TTY stdin is using
- */
-static bool is_my_tty (const char *tty)
-{
-       struct stat by_name, by_fd;
-
-       if ((stat (tty, &by_name) != 0) || (fstat (0, &by_fd) != 0)) {
-               return false;
-       }
-
-       if (by_name.st_rdev != by_fd.st_rdev) {
-               return false;
-       } else {
-               return true;
-       }
-}
 
 /*
  *     chown_tty() sets the login tty to be owned by the new user ID
  *     with TTYPERM modes
  */
 
-void chown_tty (const char *tty, const struct passwd *info)
+void chown_tty (const struct passwd *info)
 {
-       char buf[200], full_tty[200];
        char *group;            /* TTY group name or number */
        struct group *grent;
        gid_t gid;
@@ -97,18 +79,6 @@ void chown_tty (const char *tty, const struct passwd *info)
         * the group as determined above.
         */
 
-       if ('/' != *tty) {
-               snprintf (full_tty, sizeof full_tty, "/dev/%s", tty);
-               tty = full_tty;
-       }
-
-       if (!is_my_tty (tty)) {
-               SYSLOG ((LOG_WARN,
-                        "unable to determine TTY name, got %s\n", tty));
-               closelog ();
-               exit (1);
-       }
-
        if (   (fchown (STDIN_FILENO, info->pw_uid, gid) != 0)
            || (fchmod (STDIN_FILENO, getdef_num ("TTYPERM", 0600)) != 0)) {
                int err = errno;

diff --git a/libmisc/utmp.c b/libmisc/utmp.c
index c9169030cebc4e8961b7b106f23129405afbb2b5..5218a1e36476e5c5ec4c7795916796c008ca47fc 100644 (file)
--- a/libmisc/utmp.c
+++ b/libmisc/utmp.c
@@ -56,6 +56,31 @@ struct utmp utent;
 #define        NO_TTY \
        _("Unable to determine your tty name.")
 
+/*
+ * is_my_tty -- determine if "tty" is the same TTY stdin is using
+ */
+static bool is_my_tty (const char *tty)
+{
+       char full_tty[200];
+       struct stat by_name, by_fd;
+
+       if ('/' != *tty) {
+               snprintf (full_tty, sizeof full_tty, "/dev/%s", tty);
+               tty = full_tty;
+       }
+
+       if (   (stat (tty, &by_name) != 0)
+           || (fstat (STDIN_FILENO, &by_fd) != 0)) {
+               return false;
+       }
+
+       if (by_name.st_rdev != by_fd.st_rdev) {
+               return false;
+       } else {
+               return true;
+       }
+}
+
 /*
  * checkutmp - see if utmp file is correct for this process
  *
@@ -81,16 +106,20 @@ void checkutmp (bool picky)
        setutent ();
 
        /* First, try to find a valid utmp entry for this process.  */
-       while ((ut = getutent ()) != NULL)
+       while ((ut = getutent ()) != NULL) {
                if (   (ut->ut_pid == pid)
                    && ('\0' != ut->ut_line[0])
                    && ('\0' != ut->ut_id[0])
                    && (   (LOGIN_PROCESS == ut->ut_type)
-                       || (USER_PROCESS  == ut->ut_type))) {
+                       || (USER_PROCESS  == ut->ut_type))
+                   /* A process may have failed to close an entry
+                    * Check if this entry refers to this tty */
+                   && is_my_tty (ut->ut_line)) {
                        break;
                }
+       }
 
-       /* If there is one, just use it, otherwise create a new one.  */
+       /* If there is one, just use it, otherwise create a new one. */
        if (NULL != ut) {
                utent = *ut;
        } else {
@@ -110,7 +139,7 @@ void checkutmp (bool picky)
                utent.ut_type = LOGIN_PROCESS;
                utent.ut_pid = pid;
                strncpy (utent.ut_line, line, sizeof utent.ut_line);
-               /* XXX - assumes /dev/tty?? */
+               /* XXX - assumes /dev/tty?? or /dev/pts/?? */
                strncpy (utent.ut_id, utent.ut_line + 3, sizeof utent.ut_id);
                strcpy (utent.ut_user, "LOGIN");
                utent.ut_time = time (NULL);
@@ -173,6 +202,10 @@ void checkutmp (bool picky)
                 * the structure.  The UNIX/PC is broken in this regard
                 * and needs help ...
                 */
+               /* XXX: The ut_line may not match with the current tty.
+                *      ut_line will be set by setutmp anyway, but ut_id
+                *      will not be set, and the wrong utmp entry may be
+                *      updated. -- nekral */
 
                if (utent.ut_line[0] == '\0')
 #endif                         /* !UNIXPC */

diff --git a/src/login.c b/src/login.c
index 5cde73aba67416fd25ef642f414c9484f92e381d..5f3058742dcb5cfb55214c0327f30fcd6f154b33 100644 (file)
--- a/src/login.c
+++ b/src/login.c
@@ -1094,7 +1094,7 @@ int main (int argc, char **argv)
        }
        setup_limits (&pwent);  /* nice, ulimit etc. */
 #endif                         /* ! USE_PAM */
-       chown_tty (tty, &pwent);
+       chown_tty (&pwent);
 
 #ifdef USE_PAM
        /*