bin/103873: login(1) SEGFAULT on unsuccessful login

[douglas steinwand]

>Number:         103873
>Category:       bin
>Synopsis:       login(1) SEGFAULT on unsuccessful login
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Oct 01 17:20:27 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     douglas steinwand
>Release:        6.2-PRERELEASE
>Organization:
>Environment:
FreeBSD thinkpad.fx.org 6.2-PRERELEASE FreeBSD 6.2-PRERELEASE #4: Sat Sep 30 20:42:55 PDT 2006     root at thinkpad.fx.org:/usr/obj/usr/src/sys/HAWK6  i386
>Description:
It seems that the login_audit.c doesn't check that pwd is non-NULL before dereferencing it. Below is a patch with a possible solution.
>How-To-Repeat:
At the console, press Enter a few times, or run login(1) from a shell. If you do not successfuly login, the application exits and syslog notes something like:

Oct  1 10:08:51 thinkpad kernel: pid 62854 (login), uid 0: exited on signal 11

>Fix:
--- usr.bin/login/login_audit.c.orig    Tue Sep  5 16:53:21 2006
+++ usr.bin/login/login_audit.c Sun Oct  1 09:46:41 2006
@@ -51,6 +51,17 @@
  */
 static au_tid_t tid;
 
+/* returns -1 on failure, 0 on success */
+static int
+get_pwd(uid_t *uid, gid_t *gid)
+{
+       if (pwd == NULL)
+               return(-1);
+       *uid = pwd->pw_uid;
+       *gid = pwd->pw_gid;
+       return(0);
+}
+
 /*
  * The following tokens are included in the audit record for a successful
  * login: header, subject, return.
@@ -62,11 +73,14 @@
        int aufd;
        au_mask_t aumask;
        auditinfo_t auinfo;
-       uid_t uid = pwd->pw_uid;
-       gid_t gid = pwd->pw_gid;
+       uid_t uid;
+       gid_t gid;
        pid_t pid = getpid();
        long au_cond;
 
+       if (get_pwd(&uid, &gid) == -1)
+               return;
+
        /* If we are not auditing, don't cut an audit record; just return. */
        if (auditon(A_GETCOND, &au_cond, sizeof(long)) < 0) {
                if (errno == ENOSYS)
@@ -140,8 +154,8 @@
                        errx(1, "login: Audit Error: au_to_subject32() failed");
        } else {
                /* We know the subject -- so use its value instead. */
-               uid = pwd->pw_uid;
-               gid = pwd->pw_gid;
+               if (get_pwd(&uid, &gid) == -1)
+                       errx(1, "login: Audit Error: au_to_subject32() failed");
                if ((tok = au_to_subject32(uid, geteuid(), getegid(), uid,
                    gid, pid, pid, &tid)) == NULL)
                        errx(1, "login: Audit Error: au_to_subject32() failed");
@@ -172,10 +186,13 @@
        int aufd;
        au_mask_t aumask;
        auditinfo_t auinfo;
-       uid_t uid = pwd->pw_uid;
-       gid_t gid = pwd->pw_gid;
+       uid_t uid;
+       gid_t gid;
        pid_t pid = getpid();
        long au_cond;
+
+       if (get_pwd(&uid, &gid) == -1)
+               return;
 
        /* If we are not auditing, don't cut an audit record; just return. */
        if (auditon(A_GETCOND, &au_cond, sizeof(long)) < 0) {

>Release-Note:
>Audit-Trail:
>Unformatted: