macfb: fix overflow of color_palette array

The palette_current index counter has a maximum size of 256 * 3 to cover a full
color palette of 256 RGB entries. Linux assumes that the palette_current index
wraps back around to zero after writing 256 RGB entries so ensure that
palette_current is reset at this point to prevent data corruption within
MacfbState.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20211007221253.29024-5-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

diff --git a/hw/display/macfb.c b/hw/display/macfb.c
index b363bab8896a667e2bba2f839c15e039ea67f6db..39dab49026c3c1e488d35419e2dec8976b386cd2 100644 (file)
--- a/hw/display/macfb.c
+++ b/hw/display/macfb.c
@@ -303,7 +303,9 @@ static void macfb_ctrl_write(void *opaque,
         s->palette_current = 0;
         break;
     case DAFB_LUT:
-        s->color_palette[s->palette_current++] = val;
+        s->color_palette[s->palette_current] = val;
+        s->palette_current = (s->palette_current + 1) %
+                             ARRAY_SIZE(s->color_palette);
         if (s->palette_current % 3) {
             macfb_invalidate_display(s);
         }