[PATCH] libio: Ensure output buffer for wchars (bug 28828)

[Adhemerval Zanella]

On 13/02/2022 16:52, jobol@nonadev.net wrote:
> When fileops.c checks for nullity of the write pointer,
> in order to ensure its allocation, before that patch,
> wfileops didn't. This was leading to crashes on some cases,
> as described by bug 28828.
> 
> The minimal sequence to produce the crash was:
> 
>     #include <stdio.h>
>     #include <wchar.h>
>     int main(int ac, char **av)
>     {
>             setvbuf(stdout, NULL, _IOLBF, 0);
>             fgetwc(stdin);
>             fputwc(10, stdout); /*CRASH HERE!*/
>             return 0;
>     }
> 
> The line "fgetwc(stdin);" is necessary. It introduces the
> bug by setting the flag _IO_CURRENTLY_PUTTING of stdout
> indirectly (file wfileops.c, function _IO_wfile_underflow, line 213).
> 
> Signed-off-by: Jose Bollo <jobol@nonadev.net>

Patch looks ok, but git-pw fails to apply it:

$ git-pw patch apply 51088
Applying: libio: Ensure output buffer for wchars (bug 28828)
error: patch failed: libio/wfileops.c:412
error: libio/wfileops.c: patch does not apply
error: Did you hand edit your patch?

Could you resend it? 

Also, could you also provide a regression testcase for this fix?

> ---
>  libio/wfileops.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/libio/wfileops.c b/libio/wfileops.c
> index fb9d45b677..aa94a22983 100644
> --- a/libio/wfileops.c
> +++ b/libio/wfileops.c
> @@ -412,10 +412,11 @@ _IO_wfile_overflow (FILE *f, wint_t wch)
>        return WEOF;
>      }
>    /* If currently reading or no buffer allocated. */
> -  if ((f->_flags & _IO_CURRENTLY_PUTTING) == 0)
> +  if ((f->_flags & _IO_CURRENTLY_PUTTING) == 0
> +      || f->_wide_data->_IO_write_base == NULL)
>      {
>        /* Allocate a buffer if needed. */
> -      if (f->_wide_data->_IO_write_base == 0)
> +      if (f->_wide_data->_IO_write_base == NULL)
>      {
>        _IO_wdoallocbuf (f);
>        _IO_free_wbackup_area (f);