[patch] patch for privilege escalation via hardlinked symlinks

postfix-link.patch (text/plain), 2.31 KB, created by Matthias Geerdsen (RETIRED) on 2008-07-25 09:52:52 UTC

*** src/util/safe_open.c.orig	Sun Jun  4 19:04:49 2006
--- src/util/safe_open.c	Thu Jul 24 14:01:54 2008
***************
*** 83,88 ****
--- 83,89 ----
  #include <msg.h>
  #include <vstream.h>
  #include <vstring.h>
+ #include <stringops.h>
  #include <safe_open.h>
  
  /* safe_open_exist - open existing file */
***************
*** 138,150 ****
       * for symlinks owned by root. NEVER, NEVER, make exceptions for symlinks
       * owned by a non-root user. This would open a security hole when
       * delivering mail to a world-writable mailbox directory.
       */
      else if (lstat(path, &lstat_st) < 0) {
  	vstring_sprintf(why, "file status changed unexpectedly: %m");
  	errno = EPERM;
      } else if (S_ISLNK(lstat_st.st_mode)) {
! 	if (lstat_st.st_uid == 0)
! 	    return (fp);
  	vstring_sprintf(why, "file is a symbolic link");
  	errno = EPERM;
      } else if (fstat_st->st_dev != lstat_st.st_dev
--- 139,168 ----
       * for symlinks owned by root. NEVER, NEVER, make exceptions for symlinks
       * owned by a non-root user. This would open a security hole when
       * delivering mail to a world-writable mailbox directory.
+      * 
+      * The semantics of link(symlink, target) has changed over time.
+      * Traditionally, UNIX systems hardlink the target of the symlink.
+      * However, some systems hardlink the symlink itself. The latter behavior
+      * was introduced with Solaris 2.0, and with Linux kernel 2.0. Sebastian
+      * Krahmer of SuSE found that hardlinks to symlinks could be used to
+      * append mail for root to a sensitive file. For this reason, we not
+      * only require that a symlink is owned by root, but we now also require
+      * that its parent directory is writable only by root.
       */
      else if (lstat(path, &lstat_st) < 0) {
  	vstring_sprintf(why, "file status changed unexpectedly: %m");
  	errno = EPERM;
      } else if (S_ISLNK(lstat_st.st_mode)) {
! 	if (lstat_st.st_uid == 0) {
! 	    struct stat parent_st;
! 	    const char *parent;
! 
! 	    parent = sane_dirname((VSTRING *) 0, path);
! 	    if (stat(parent, &parent_st) == 0	/* real parent */
! 		&& parent_st.st_uid == 0
! 		&& (parent_st.st_mode & (S_IWGRP | S_IWOTH)) == 0)
! 		return (fp);
! 	}
  	vstring_sprintf(why, "file is a symbolic link");
  	errno = EPERM;
      } else if (fstat_st->st_dev != lstat_st.st_dev