linux-kernel - Re: [PATCH] speakup: Fix 8bit characters from direct synth

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Message-ID: <20240204001645.oj44wnx3ifk2l7tg@begin>
Date: Sun, 4 Feb 2024 01:16:45 +0100
From: Samuel Thibault <samuel.thibault@...-lyon.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, speakup@...ux-speakup.org
Subject: Re: [PATCH] speakup: Fix 8bit characters from direct synth

Greg KH, le sam. 03 févr. 2024 16:03:20 -0800, a ecrit:
> On Sun, Feb 04, 2024 at 12:36:00AM +0100, Samuel Thibault wrote:
> > When userland echoes 8bit characters to /dev/synth with e.g.
> > 
> > echo -e '\xe9' > /dev/synth
> > 
> > synth_write would get characters beyond 0x7f, and thus negative when
> > char is signed.  When given to synth_buffer_add which takes a u16, this
> > would sign-extend and produce a U+ffxy character rather than U+xy.
> > Users thus get garbled text instead of accents in their output.
> > 
> > Let's fix this by making sure that we read unsigned characters.
> > 
> > Signed-off-by: Samuel Thibault <samuel.thibault@...-lyon.org>
> > Fixes: 89fc2ae80bb1 ("speakup: extend synth buffer to 16bit unicode characters")
> > Cc: stable@...r.kernel.org
> > 
> > ---
> >  drivers/accessibility/speakup/synth.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > --- a/drivers/accessibility/speakup/synth.c
> > +++ b/drivers/accessibility/speakup/synth.c
> > @@ -208,8 +208,9 @@ void spk_do_flush(void)
> >  	wake_up_process(speakup_task);
> >  }
> >  
> > -void synth_write(const char *buf, size_t count)
> > +void synth_write(const char *_buf, size_t count)
> >  {
> > +	const unsigned char *buf = (const unsigned char *) _buf;
> >  	while (count--)
> >  		synth_buffer_add(*buf++);
> >  	synth_start();
> 
> Nit, I think you need a blank line after the new variable definition.

Ok.

> And why can't we just change these to be u8 instead of "char"?  Wouldn't
> that solve this issue overall better?

I was wondering, but an example of caller is synth_direct_store, which
calls string_unescape_any_inplace on the buffer, which does take a char*
and I guess won't change.

Samuel