linprocfs proc/pid/environ patch & list question

[Fernando Apesteguía]

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.

>>
>> 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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