On Wed, 2018-07-11 at 13:21 -0400, Frediano Ziglio wrote:
> >
> > On Tue, 2018-07-10 at 14:35 +0100, Frediano Ziglio wrote:
> > > Check we have enough data before reading.
> >
> > Check *that* we have...
> >
>
> updated, thanks
>
> > > This could lead to read buffer overflows being undetected.
> > > This is not a security issue, read happens only in the client not
> > > causing
> > > any information leakage, maximum can generate a crash or some
> > > garbage
> > > on
> > > the screen.
> > >
> > > Signed-off-by: Frediano Ziglio <fziglio@xxxxxxxxxx>
> > > ---
> > > common/canvas_base.c | 23 +++++++++++++++++++----
> > > 1 file changed, 19 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/common/canvas_base.c b/common/canvas_base.c
> > > index 05c4e1f..ae07625 100644
> > > --- a/common/canvas_base.c
> > > +++ b/common/canvas_base.c
> > > @@ -537,6 +537,9 @@ static pixman_image_t
> > > *canvas_get_lz4(CanvasBase
> > > *canvas, SpiceImage *image)
> > > width = image->descriptor.width;
> > > stride_encoded = width;
> > > height = image->descriptor.height;
> > > + if (data + 2 > data_end) {
> > > + return NULL;
> >
> > All other error conditions that you handle below print a warning.
> > Do
> > you want one here as well?
> >
> > Acked-by: Jonathon Jongsma <jjongsma@xxxxxxxxxx>
> >
>
> does
>
> g_warning("missing header in LZ4 data");
>
> look fine?
>
Yeah, that sounds fine.
Jonathon
> Frediano
>
> >
> > > + }
> > > top_down = !!*(data++);
> > > spice_format = *(data++);
> > > switch (spice_format) {
> > > @@ -579,16 +582,22 @@ static pixman_image_t
> > > *canvas_get_lz4(CanvasBase *canvas, SpiceImage *image)
> > > bits = dest;
> > >
> > > do {
> > > + if (data + 4 > data_end) {
> > > + goto format_error;
> > > + }
> > > // Read next compressed block
> > > enc_size = read_uint32_be(data);
> > > data += 4;
> > > + /* check overflow. This check is a bit different to
> > > avoid
> > > + * possible overflows. From previous check data_end -
> > > data
> > > cannot overflow.
> > > + * Computing data + enc_size on 32 bit could cause
> > > overflows. */
> > > + if (enc_size < 0 || data_end - data < (unsigned int)
> > > enc_size) {
> > > + goto format_error;
> > > + }
> > > dec_size = LZ4_decompress_safe_continue(stream, (const
> > > char
> > > *) data,
> > > (char *) dest,
> > > enc_size, available);
> > > if (dec_size <= 0) {
> > > - spice_warning("Error decoding LZ4 block\n");
> > > - pixman_image_unref(surface);
> > > - surface = NULL;
> > > - break;
> > > + goto format_error;
> > > }
> > > dest += dec_size;
> > > available -= dec_size;
> > > @@ -599,6 +608,12 @@ static pixman_image_t
> > > *canvas_get_lz4(CanvasBase
> > > *canvas, SpiceImage *image)
> > >
> > > LZ4_freeStreamDecode(stream);
> > > return surface;
> > > +
> > > +format_error:
> > > + spice_warning("Error decoding LZ4 block\n");
> > > + LZ4_freeStreamDecode(stream);
> > > + pixman_image_unref(surface);
> > > + return NULL;
> > > }
> > > #endif
> > >
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