[FFmpeg-devel] [PATCH] swscale: avoid overread in planar2x

Michael Niedermayer michaelni
Sun Sep 12 12:44:24 CEST 2010

On Sun, Sep 12, 2010 at 12:11:20PM +0200, Michael Niedermayer wrote:
> On Sun, Sep 12, 2010 at 12:11:58AM -0300, Ramiro Polla wrote:
> > Hi,
> > 
> > The MMX2/3dnow code in planar2x in rgb2rgb currently reads one byte
> > prior to the source buffer. This leads to a crash on Windows and Mac
> > OS X when the buffer is allocated on the beginning of a page. This
> > should also be a problem on Linux but I haven't seen many crashes
> > because of overreading...
> the code looks buggy
> the first pixel should be [0] not [-1] that can be achived by
> moving the reading code of it to the end of the loop and constructing
> the contents of the first mm4 outside the loop

after a second look i see that the C code overrides the first pixel and thus
the output should not be affected, still my suggestion though seems nicer than
requireing all buffers to have a byte allocated before them

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

it is not once nor twice but times without number that the same ideas make
their appearance in the world. -- Aristotle
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