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

[José Bollo]

On Mon, 14 Feb 2022 11:15:46 -0300
Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote:

> 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?

I copied the ouput of [git format-patch], following as much as possible
https://sourceware.org/glibc/wiki/Contribution%20checklist but didn't
used [git send-email]. I don't have the command [git pw] that you are
using. I can see that [git apply] produce the same issue but [git am]
perfectly works.

> Could you resend it? 

I can try but maybe you have a hint avoiding me to do the same...

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

Why not. Where? a libio/bug-XXX.c ?

> > ---
> >  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);