Re: [PATCH v2] Cygwin: spawn: Fix segfalt when too many command line args are specified.

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Aug 28 13:09, Corinna Vinschen wrote:
> On Aug 28 12:57, Corinna Vinschen wrote:
> > On Aug 28 18:46, Takashi Yano wrote:
> > > Previously, the number of command line args was not checked for
> > > cygwin process. Due to this, segmentation fault was caused if too
> > > many command line args are specified.
> > > https://cygwin.com/pipermail/cygwin/2023-August/254333.html
> > > 
> > > Since char *argv[argc + 1] is placed on the stack in dll_crt0_1(),
> > > STATUS_STACK_OVERFLOW occurs if the stack does not have enough
> > > space.
> > > 
> > > With this patch, the total length of the arguments and the size of
> > > argv[] is restricted to 1/4 of total stack size for the process, and
> > > spawnve() returns E2BIG if the size exceeds the limit.
> > > [...]
> > I tried this simple patch:
> > 
> > diff --git a/winsup/cygwin/dcrt0.cc b/winsup/cygwin/dcrt0.cc
> > index 49b7a44aeb15..961dea4ab993 100644
> > --- a/winsup/cygwin/dcrt0.cc
> > +++ b/winsup/cygwin/dcrt0.cc
> > @@ -978,11 +978,8 @@ dll_crt0_1 (void *)
> >  	 a change to an element of argv[] it does not affect Cygwin's argv.
> >  	 Changing the the contents of what argv[n] points to will still
> >  	 affect Cygwin.  This is similar (but not exactly like) Linux. */
> > -      char *newargv[__argc + 1];
> > -      char **nav = newargv;
> > -      char **oav = __argv;
> > -      while ((*nav++ = *oav++) != NULL)
> > -	continue;
> > +      char **newargv = (char **) malloc ((__argc + 1) * sizeof (char **));
> > +      memcpy (newargv, __argv, (__argc + 1) * sizeof (char **));
> >        /* Handle any signals which may have arrived */
> >        sig_dispatch_pending (false);
> >        _my_tls.call_signal_handler ();
> > 
> > and the testcase `LC_ALL=C sed 's/x/y/' $(seq 1000000)' simply ran
> > as desired.  Combined with a bit of error checking...
> 
> We may also get away with storing it in the Windows heap, but I didn't
> test this .

No, we don't. The Windows heap would not be inherited by a forked
child and argv would be lost.  Sounds not great.


Corinna