Re: [gentoo-amd64] Re: Installing into a 32-bit chroot?

[Billy Holmes <billy@gonoph.net>]

Tres Melton wrote:
> the /tmp dirs and other things and I do this at boot.  Further I have
> written a program that will allow any user (approved by the sudoers file
> in the chroot and the regular root) to run any program from wherever
> they are without the headache of becoming root, etc..  Here ya go:

I actually did the same thing, but I'm combined some code from chroot 
and linux32 and made my own "l32".

install as:
# install -o root -g root -m 4555 l32 $BIN_DIR

invoke as:
$ l32 $PROGRAM

If it can't change into the CWD from the chroot (I use mount --bind for 
/home and /tmp), then it changes in to the chroot's "/" directory.

Change "LOWDIR" to point to your own 32-bit chroot.

---[snip]---
#include <linux/personality.h>
#undef personality
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>

/* Make --3gb the default for buggy Java */
#define STUPID_DEFAULT 1
#define  PER_LINUX32_3GB       (PER_LINUX32 | ADDR_LIMIT_32BIT)

#ifdef STUPID_DEFAULT
#define DFL_PER PER_LINUX32_3GB
#else
#define DFL_PER PER_LINUX32
#endif

const char *LOWDIR="/home/32-bit";
#define malloc_Add	64
#define malloc_Max	INT_MAX>>12	// If it's over 512 kb, then path is too big

int main(int argc,char **argv,char **envp)
{
   int per=DFL_PER;
   char *PWD;
   size_t PWD_size=malloc_Add;

   if (personality(per) < 0)
   {
     fprintf(stderr,"Can't set personality %x : %s\n",per,strerror(errno));
     exit(-1);
   }
   if (argc<2)
   {
     fprintf(stderr,"Usage: %s program (arg1 arg2 arg3 ...)\n",argv[0]);
     exit(-1);
   }
   PWD=malloc(PWD_size);
   while (NULL==getcwd(PWD,PWD_size))
   {
     if (errno==ERANGE)
     {
       if (PWD_size+malloc_Add>malloc_Max)
       {
	fprintf(stderr,"Path is too long: greater than %lu bytes\n",PWD_size);
	exit(-1);
       }
       PWD_size+=malloc_Add;
       PWD=realloc(PWD,PWD_size);
     } else {
       fprintf(stderr,"Unable to determine current working directory: 
%s\n",strerror(errno));
       exit(-1);
     }
   }
   if (chroot(LOWDIR) < 0)
   {
     fprintf(stderr,"Unable to chroot(%s): %s\n",LOWDIR,strerror(errno));
     exit(-1);
   }
   if (seteuid(getuid()) < 0)
   {
     fprintf(stderr,"Unable to suid(%d): %s\n",getuid(),strerror(errno));
     exit(-1);
   }
   // now change into current working dir with no root privs
   if (chdir(PWD) && chdir("/"))
   {
     fprintf(stderr,"Unable to set working directory: 
%s\n",strerror(errno));
     exit(-1);
   }
   free(PWD);
   execvp(argv[1],argv+1);
   exit(-1);
}
// vim: sw=2:cindent:
-- 
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