Midnight Commander


    Linux with mc 4.xx


    Maurycy Prodeus found following.  He tested 4.1.33.  You can  make
    a Segmentation  Fault and  if root  doesn't lock  this , it causes
    Core Dumping... of course you just make some file in /tmp (?)  and
    if root read this file ...  his mc creates core... yeesss you  can
    make symlink to  every file in  system ... and  this file will  be
    totaly  destroyed!   Together  with  "Social  Engeering",  it   is
    dangerous. [filename may be  example: or sth.]   What
    file we must create?  With negative size , but really it should be
    a very large size  (very strange that even  in kernel 2.2.5 it  is
    posible to do that).  Quick  test: Run program below and then  run
    mc and try to read [F3 of course and example PageDown] file  which
    was created by mc-kill ...

    /* mc-kill.c */

    #include <sys/file.h>
    #include <stdio.h>
    #define size -900000

    main(int argc,char* argv[]) {
      int i;
      if (!argv[1]) {
	printf("\nUSAGE : %s filename[and patch] \n\n",argv[0]);

    If you use above program (or /dev/zero) you may fill partition ...
    When crontab is reading file, it creates temp in  /var/spool/cron/
    (non-root can't even  read this), but,  if it doesn't  finish then
    doesn't delete this  temp file...   So, we must  give crontab file
    with "infinit" size.  Example:

	crontab -file-made-by-mc-kill


    You should NEVER read  strange file in MC.   You should NEVER  use
    mc as root as well.   lcamtuf wrote kernel module which not  allow
    to create symlinks in /tmp:

    Looking   at   the   2.0.36   source,   there   is   no  check  in
    fs/open.c:do_truncate so assume it that is vulnerable too.  Recent
    linux  2.2.x  kernels  seem  OK.   A  patch  to  fix 2.0.x this is
    appended below (against 2.0.36).  Its just a cut and paste of  the
    relevant code from recent kernels.

    --- linux/fs/open.c~    Sat Nov 30 23:21:19 1996
    +++ linux/fs/open.c     Mon Apr 19 12:44:47 1999
    @@ -68,6 +68,11 @@
	    int error;
	    struct iattr newattrs;

    +        /* Not pretty: "inode->i_size" shouldn't really be "off_t". But it is. */
    +        if ((off_t) length < 0)
    +               return -EINVAL;
	    newattrs.ia_size = length;
	    newattrs.ia_valid = ATTR_SIZE | ATTR_CTIME;