Changes in fork ?

[Sergey Kubushin]

On Fri, 21 Jan 2000, Richard B. Johnson wrote:

Thank you for your reply. Now I do have an overall idea how to get sendmail,
inetd and several another apps fixed.

> On Fri, 21 Jan 2000, Sergey Kubushin wrote:
> 
> > Hi, everybody!
> > 
> > I have a question about fork() (?) behaviour. The problem shows itself as
> > truncated lines in ps output on processes that are forked outta daemons
> > which use setproctitle() (from sendmail sources) such as sendmail, inetd
> > etc. All's fine on 2.2.xx kernels, but I have the following under 2.3.xx :
> > 
> > === Cut ===
> > 22352  ?  S    0:00 sendmail: accepting connectio
> > 22353  ?  S    0:00  \_ sendmail: LAA14150 relay1.cha
> > .
> > .
> > .
> >   701  ?  S    0:13 inetd
> >  2765  ?  S    0:01  \_ ftpd: 19
> >  5294  ?  S    0:00  \_ ftpd: sa
> > 13547  ?  S    0:00  \_ ftpd: fi
> > 14656  ?  S    0:00  \_ ftpd: 19
> > 14760  ?  S    0:00  \_ ftpd: 21
> > 15685  ?  S    0:00  \_ ftpd: sa
> > 16160  ?  S    0:00  \_ ftpd: at
> > 18482  ?  S    0:00  \_ ftpd: 21
> > .
> > .
> > .
> > === Cut ===
> > 
> 
> Yes. This was previously reported by myself. Basically, what the
> daemons are doing is:
> 
> 	int main (int argc, *argv[])
>         {                 /* setproctitle() */
>             strcpy(argv[0], "New Name to be seen by `ps`");
> 
> This is NotGood(tm) because no child knows how much space was
> available for the string. However, it's been done for ages. New
> /proc/###/cmdline code (where `ps` gets the command-line), now
> only allows you to read the length of the initial allocation.
> 
> The `fix` is not a kernel fix. Any child of a parent which desires
> to overwrite argv[0], has to make sure the parent has enough space
> allocated. This means that the child should be kicked-off with
> its own arguments, with enough space allocated like:
> 
> 	parent's main(int args, char *argv[])
>         {
>             extract_command_line_pars(args, argv);  /* Do first */
> 
>             argv[0] = buffer0[0x100];     /* Replace pointers */
>             argv[1] = buffer1[0x100];
>             argv[2] = NULL;
> 
>             switch(fork())
>             {
>             case 0:    /* child */
>                  strncpy(argv[0], "New stuff", 0x100);
> 
> 
> If you fix all the `parent` daemons, you will have a good `ps` output.
> Here is an example, program `status` before/after.
> 
> PID   Name            Stat  CPU     Mem   Exe   Command line
> 1     (init)          S     0.02    220   188   init [5]  
> 2     (kswapd)        S     0.00    220   188             
> 3     (kflushd)       S     0.00    220   188             
> 4     (kupdate)       S     0.00    220   188             
> 40    (crond)         S     0.04    844   0     /usr/sbin/crond 
> 59    (klogd)               0.02    796   20    /usr/sbin/klogd -s -k /System.ma
> [Snipped...]
> 
> 15241 (status)        R     0.00    712   4     really big command
>                                                 ^^^^^^^^^^^^^^^^ Truncated
> 15625 (pine)          S     0.14    2688  0     pine      
> 15754 (status)        R     0.01    712   4     really big command
> line that _has_a_lot_of_stuff_in_it    
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Fixed.
> 
> Cheers,
> Dick Johnson
> 
> Penguin : Linux version 2.3.39 on an i686 machine (800.63 BogoMips).
> 

===========================================================================
Sergey Kubushin aka the Tamer         < > The impossible we do immediately.
e-mail: ksi en ksi-linux.com  SK320-RIPE < > Miracles require 24-hour notice.
===========================================================================


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