Changes in fork ?

[Nick Holloway]

root en chaos.analogic.com (Richard B. Johnson) writes:
> On Fri, 21 Jan 2000, Sergey Kubushin wrote:
> > 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
> 
> 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.

Normally the implementations of setproctitle() are a little more careful
than that.  They use the processes environment space in addition to the
argument space.  This does rely on them being contiguous memory areas.

Looking as binfmt_elf and binfmt_aout, this still appears to be true in
2.3.40, so the previous behaviour can be restored by limiting the area
returned in /proc/$$/cmdline to be env_end, instead of arg_end.

Note that the contents returned in /proc/$$/environ are already trashed
by code that uses setproctitle().

--- /usr/src/linux-2.3/fs/proc/base.c	Sun Jan 23 10:50:53 2000
+++ base.c	Sun Jan 23 11:45:03 2000
@@ -120,7 +120,7 @@
 	struct mm_struct *mm = task->mm;
 	int res = 0;
 	if (mm) {
-		int len = mm->arg_end - mm->arg_start;
+		int len = mm->env_end - mm->arg_start;
 		if (len > PAGE_SIZE)
 			len = PAGE_SIZE;
 		res = access_process_vm(task, mm->arg_start, buffer, len, 0);

-- 
 `O O'  | Nick.Holloway en alfie.demon.co.uk
// ^ \\ | http://www.alfie.demon.co.uk/

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