svn commit: r301580 - head/sys/kern

[Konstantin Belousov]

Author: kib
Date: Wed Jun  8 04:37:03 2016
New Revision: 301580
URL: https://svnweb.freebsd.org/changeset/base/301580

Log:
  Old process credentials for setuid execve must not be dereferenced
  when the process credentials were not changed.  This can happen if an
  error occured trying to activate the setuid binary.  And on error, if
  new credentials were not yet assigned, they must be freed to not
  create the leak.
  
  Use oldcred == NULL as the predicate to detect credential
  reassignment.
  
  Reported and tested by:	pho
  Sponsored by:	The FreeBSD Foundation

Modified:
  head/sys/kern/kern_exec.c

Modified: head/sys/kern/kern_exec.c
==============================================================================
--- head/sys/kern/kern_exec.c	Wed Jun  8 04:18:57 2016	(r301579)
+++ head/sys/kern/kern_exec.c	Wed Jun  8 04:37:03 2016	(r301580)
@@ -806,8 +806,11 @@ interpret:
 	/*
 	 * Set the new credentials.
 	 */
-	if (imgp->newcred != NULL)
+	if (imgp->newcred != NULL) {
 		proc_set_cred(p, imgp->newcred);
+		crfree(oldcred);
+		oldcred = NULL;
+	}
 
 	/*
 	 * Store the vp for use in procfs.  This vnode was referenced by namei
@@ -918,8 +921,9 @@ exec_fail:
 		SDT_PROBE1(proc, , , exec__failure, error);
 	}
 
-	if (imgp->newcred != NULL)
-		crfree(oldcred);
+	if (imgp->newcred != NULL && oldcred != NULL)
+		crfree(imgp->newcred);
+
 #ifdef MAC
 	mac_execve_exit(imgp);
 	mac_execve_interpreter_exit(interpvplabel);