[vlc-devel] [PATCH] decoder: thumbnailer: Fix unprotected access to b_first

[Thomas Guillem]

On Wed, Oct 2, 2019, at 07:53, Steve Lhomme wrote:
> Maybe an atomic bool would be more appropriate  ?

No, for the main usecase (video playback), this variable need to be read/write with this lock alongside other variables.

> 
> On 2019-10-01 18:33, Hugo Beauzée-Luyssen wrote:
> > ---
> >   src/input/decoder.c | 17 +++++++++++++----
> >   1 file changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/src/input/decoder.c b/src/input/decoder.c
> > index 57c9de6a1e..bb1beca38d 100644
> > --- a/src/input/decoder.c
> > +++ b/src/input/decoder.c
> > @@ -1101,19 +1101,28 @@ static picture_t *thumbnailer_buffer_new( decoder_t *p_dec )
> >       struct decoder_owner *p_owner = dec_get_owner( p_dec );
> >       /* Avoid decoding more than one frame when a thumbnail was
> >        * already generated */
> > +    vlc_mutex_lock( &p_owner->lock );
> >       if( !p_owner->b_first )
> > +    {
> > +        vlc_mutex_unlock( &p_owner->lock );
> >           return NULL;
> > +    }
> > +    vlc_mutex_unlock( &p_owner->lock );
> >       return picture_NewFromFormat( &p_dec->fmt_out.video );
> >   }
> >   
> >   static void ModuleThread_QueueThumbnail( decoder_t *p_dec, picture_t *p_pic )
> >   {
> >       struct decoder_owner *p_owner = dec_get_owner( p_dec );
> > -    if( p_owner->b_first )
> > -    {
> > +    bool b_first;
> > +
> > +    vlc_mutex_lock( &p_owner->lock );
> > +    b_first = p_owner->b_first;
> > +    p_owner->b_first = false;
> > +    vlc_mutex_unlock( &p_owner->lock );
> > +
> > +    if( b_first )
> >           decoder_Notify(p_owner, on_thumbnail_ready, p_pic);
> > -        p_owner->b_first = false;
> > -    }
> >       picture_Release( p_pic );
> >   
> >   }
> > -- 
> > 2.20.1
> > 
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