[PATCH v2] Cygwin: spawn: Fix segfalt when too many command line args are specified.
Corinna Vinschen
corinna-cygwin@cygwin.com
Mon Aug 28 11:09:18 GMT 2023
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 .
> Along these lines, there's no reason to couple SC_ARG_MAX to the
> size of the stack. I'd propose to return the value 2097152. It's
> the default value returned by getconf ARG_MAX on LInx as well.
Oh, and we can carefully check in child_info_spawn::worker that
the args are not taking more space than the value returned by
SC_ARG_MAX and return E2BIG if so. We do this when checking the
args for non-Cygwin apps anyway.
Thanks,
Corinna
More information about the Cygwin-patches
mailing list