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Date:	Mon, 28 Apr 2025 23:18:20 -0700 (PDT)
X-X-Sender:	jeremyd AT resin DOT csoft DOT net
To:	cygwin AT cygwin DOT com
Subject:	Re: cygwin_conv_path with size 0
In-Reply-To:	<9c8107b6-a040-d956-2590-ede1517bc2ad@jdrake.com>
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From:	Jeremy Drake via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Jeremy Drake <cygwin AT jdrake DOT com>
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On Mon, 28 Apr 2025, Jeremy Drake via Cygwin wrote:

> I was just describing cygwin_conv_path on a rust issue
> (https://github.com/rust-lang/backtrace-rs/pull/704).  I was saying that
> the pointer `to` is not accessed when `size` is 0, but it turns out on
> circa line 4022 in path.cc
>
> to = (void *) wcpcpy ((wchar_t *) to, ro_u_globalroot.Buffer);
>
> This is before `size` is checked and lsiz returned if it was zero, or
> ENOSPC set if size is too small, circa line 4060.  This seems like a bug
> to me.

Yep, test case

#include <stdio.h>
#include <sys/cygwin.h>

int main(void)
{
  wchar_t *buf = cygwin_create_path (CCP_POSIX_TO_WIN_W, "/dev/sda");
  if (!buf)
  {
    perror ("cygwin_create_path");
    return 1;
  }
  printf("%ls\n", buf);
  return 0;
}



cygwin_create_path: Bad address


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