[PATCH v4] libio: Ensure output buffer for wchars (bug 28828)

[Adhemerval Zanella]

On 08/03/2022 05:58, jobol@nonadev.net wrote:
> From: José Bollo <jobol@nonadev.net>
> 
> 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>

This patch looks ok, I will fix the style issues below and install it.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  libio/Makefile          |  2 +-
>  libio/tst-bz28828.c     | 33 +++++++++++++++++++++++++++++++++
>  libio/tst-bz28828.input |  1 +
>  libio/wfileops.c        |  3 ++-
>  4 files changed, 37 insertions(+), 2 deletions(-)
>  create mode 100644 libio/tst-bz28828.c
>  create mode 100644 libio/tst-bz28828.input
> 
> diff --git a/libio/Makefile b/libio/Makefile
> index 0e5f348bea..e97387743f 100644
> --- a/libio/Makefile
> +++ b/libio/Makefile
> @@ -66,7 +66,7 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \
>  	tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
>  	tst-ftell-append tst-fputws tst-bz22415 tst-fgetc-after-eof \
>  	tst-sprintf-ub tst-sprintf-chk-ub tst-bz24051 tst-bz24153 \
> -	tst-wfile-sync
> +	tst-wfile-sync tst-bz28828
>  
>  tests-internal = tst-vtables tst-vtables-interposed
>  
> diff --git a/libio/tst-bz28828.c b/libio/tst-bz28828.c
> new file mode 100644
> index 0000000000..22a70dd954
> --- /dev/null
> +++ b/libio/tst-bz28828.c
> @@ -0,0 +1,33 @@
> +/* Unit test for BZ#28828.
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <support/xstdio.h>
> +#include <support/check.h>
> +#include <wchar.h>
> +
> +static int
> +do_test (void)
> +{ 

Extra space after '{'.

> +  setvbuf(stdout, NULL, _IOLBF, 0);

Space after before '(', also for the rest on function calls.

> +  fgetwc(stdin);
> +  fputwc(10, stdout); /*SHOUDN'T CRASH HERE!*/

We usually do not add comments in upper cases, I will replace with.

  /* It should not crash here.  */

> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> +

Extra newline.

> diff --git a/libio/tst-bz28828.input b/libio/tst-bz28828.input
> new file mode 100644
> index 0000000000..ce01362503
> --- /dev/null
> +++ b/libio/tst-bz28828.input
> @@ -0,0 +1 @@
> +hello
> diff --git a/libio/wfileops.c b/libio/wfileops.c
> index fb9d45b677..b59a98881f 100644
> --- a/libio/wfileops.c
> +++ b/libio/wfileops.c
> @@ -412,7 +412,8 @@ _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)

Ok.