process 'ld-linux-x86-64' launched '/tmp/testscriptWLyRCA' with NULL argv: empty string added

process 'ld-linux-x86-64' launched '/tmp/testscriptWLyRCA' with NULL argv: empty string added

[Cristian Rodríguez]

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Hi:

Apparently  posix/tst-execvpe6.c is not valid anymore at least on linux
where  NULL argv is invalid. The kernel is way too nice and not killing the
process as it should but using an empty string instead.

so,

 char *args3[] = { NULL };
  if (run_script (fname2, args3))
    return 1;

is testing..

 char *args3[] = { "", NULL };
  if (run_script (fname2, args3))
    return 1;

instead.

Re: process 'ld-linux-x86-64' launched '/tmp/testscriptWLyRCA' with NULL argv: empty string added

[Adhemerval Zanella Netto]

On 03/05/23 16:17, Cristian Rodríguez via Libc-alpha wrote:
> Hi:
> 
> Apparently  posix/tst-execvpe6.c is not valid anymore at least on linux
> where  NULL argv is invalid. The kernel is way too nice and not killing the
> process as it should but using an empty string instead.
> 
> so,
> 
>  char *args3[] = { NULL };
>   if (run_script (fname2, args3))
>     return 1;
> 
> is testing..
> 
>  char *args3[] = { "", NULL };
>   if (run_script (fname2, args3))
>     return 1;
> 
> instead.


My understanding is kernel will append an empty string to avoid breaking
userspace:

fs/exec.c:

1919         retval = count(argv, MAX_ARG_STRINGS);
1920         if (retval == 0)
1921                 pr_warn_once("process '%s' launched '%s' with NULL argv: empty string added\n",
1922                              current->comm, bprm->filename);
[...]
1949         /*
1950          * When argv is empty, add an empty string ("") as argv[0] to
1951          * ensure confused userspace programs that start processing
1952          * from argv[1] won't end up walking envp. See also
1953          * bprm_stack_limits().
1954          */
1955         if (bprm->argc == 0) {
1956                 retval = copy_string_kernel("", bprm);
1957                 if (retval < 0)
1958                         goto out_free;
1959                 bprm->argc = 1;
1960         }

So this is not really 'invalid'.