Re: PATCH: cdrecord: avoiding scsi device numbering for ide devices

[Andreas Steinmetz]

Kyle Moffett wrote:
> Chosen solution for 2.6.8.1:
>     Only allow certain known-safe commands, anything else needs
> root privileges, specifically CAP_SYS_RAWIO or CAP_SYS_ADMIN,
>  (Seems sane, and follows with the general design of the  rest of the
> kernel).

To make this clear first: I don't want to step on anyone's toes.

So here is a snippet of code that should work nicely on 2.4 and 2.6 (the 
latter with the sanitized kernel headers) to set the required 
capabiltities in a setuid() wrapper:

#include <unistd.h>
#include <linux/capability.h>
#include <sys/prctl.h>
extern int capset(cap_user_header_t header, const cap_user_data_t data);

int do_setuid(uid_t uid)
{
  int r;
  struct __user_cap_header_struct h;
  struct __user_cap_data_struct c;

  if(geteuid())return setuid(uid);
  memset(&h,0,sizeof(h));
  h.version=_LINUX_CAPABILITY_VERSION;
  h.pid=0;
  memset(&c,0,sizeof(c));
  c.effective=1<<CAP_SYS_RAWIO|1<<CAP_SYS_ADMIN|1<<CAP_SETUID;
  c.permitted=1<<CAP_SYS_RAWIO|1<<CAP_SYS_ADMIN|1<<CAP_SETUID;
  c.inheritable=0;
  capset(&h,&c);
  prctl(PR_SET_KEEPCAPS,1,0,0,0);
  r=setuid(uid);
  memset(&h,0,sizeof(h));
  h.version=_LINUX_CAPABILITY_VERSION;
  h.pid=0;
  memset(&c,0,sizeof(c));
  c.effective=1<<CAP_SYS_RAWIO|1<<CAP_SYS_ADMIN;
  c.permitted=1<<CAP_SYS_RAWIO|1<<CAP_SYS_ADMIN;
  c.inheritable=0;
  capset(&h,&c);
  prctl(PR_SET_KEEPCAPS,0,0,0,0);
  return r;
}

Now this is what free software is all about. Reuse of knowledge for 
everyone. Jörg, feel free to use the above code. Note that the 
CAP_SETUID usage is a workaround for a 2.4 bug.
--
Andreas Steinmetz                       SPAMmers use robotrap@xxxxxxxx
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