linprocfs proc/pid/environ patch & list question

[Kostik Belousov]

On Thu, Feb 18, 2010 at 06:48:35PM +0100, Fernando Apestegu?a wrote:
> On Wed, Feb 17, 2010 at 8:11 PM, Kostik Belousov <kostikbel at gmail.com> wrote:
> > On Wed, Feb 17, 2010 at 07:51:06PM +0100, Fernando Apestegu?a wrote:
> >> Hi,
> >>
> >> I have a small patch (against 8.0-RELEASE-p2) that _should_ implement
> >> the /proc/pid/environ file
> >> under linprocfs.
> >> However, it seems it does not work properly but I don't know what I'm
> >> doing wrong.
> >> Is this list the place to ask for help? I tried in the forums[1] but
> >> got no answer.
> > Putting aside any "does not work" questions, please see comment below.
> 
> Sorry I didn't explain this. If I have a process forked from bash
> shell in which I have
> exported VAR=XXXX the /compat/linux/proc/pid/environ for the child process
> does not show the VAR variable.
Copyin copies the data from the address space of the current process.
You are interested in the content of address space of different process.
Look at the proc_rwmem().

> 
> >>
> >> Don't we have a 'kernel newbies'-like list?
> >>
> >> Thanks in advance.
> >>
> >> [1] http://forums.freebsd.org/showthread.php?t=11329
> >>
> >> --- sys/compat/linprocfs/linprocfs.c.orig     2009-10-25 02:10:29.000000000 +0100
> >> +++ sys/compat/linprocfs/linprocfs.c  2010-02-16 19:38:36.000000000 +0100
> >> @@ -939,8 +939,38 @@
> >>  static int
> >>  linprocfs_doprocenviron(PFS_FILL_ARGS)
> >>  {
> >> +     int i, error;
> >> +     struct ps_strings pss;
> >> +     char **ps_envstr;
> >>
> >> -     sbuf_printf(sb, "doprocenviron\n%c", '\0');
> >> +     PROC_LOCK(p);
> >> +     if (p_cansee(td, p) != 0)
> >> +             return (0);
> >> +     PROC_UNLOCK(p);
> >> +
> >> +     error = copyin((void *)p->p_sysent->sv_psstrings, &pss,
> >> +                                         sizeof(pss));
> >> +     if (error)
> >> +             return (error);
> >> +
> >> +     ps_envstr = malloc(pss.ps_nenvstr * sizeof(char *),
> >> +         M_TEMP, M_WAITOK);
> > This is essentially "panic me" code.  ps_nenvstr is user-controlled,
> > and allows to specify arbitrary integers.
> >
> > Even ignoring exhaustion of the kernel map, it can cause allocation of
> > big amount of physical memory. Note that execve(2) implementation uses
> > swappable memory to store arguments and environment strings passed from
> > vm spaces.
> 
> Thanks for the comment. If I want to check ps_envstr, which threshold would be
> reasonable? PAGE_SIZE maybe?
> 
> Thanks again.
> 
> >
> >> +
> >> +     error = copyin((void *)pss.ps_envstr, ps_envstr,
> >> +         pss.ps_nenvstr * sizeof(char *));
> >> +
> >> +     if (error) {
> >> +             free(ps_envstr, M_TEMP);
> >> +             return (error);
> >> +     }
> >> +
> >> +     /* NULL separated list of variable=value pairs */
> >> +
> >> +     for (i = 0; i < pss.ps_nenvstr; i++) {
> >> +             sbuf_copyin(sb, ps_envstr[i], 0);
> >> +     }
> >> +
> >> +     free(ps_envstr, M_TEMP);
> >>       return (0);
> >>  }
> >> _______________________________________________
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> >
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