tiff: Check that there is no aliasing in pixel format selection

Fixes possible issues with unexpected bpp/bppcount values.

CC: libav-stable@libav.org
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Bug-Id: CVE-2014-8544
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/tiff.c

@@ -252,6 +252,14 @@ static int init_image(TiffContext *s, AVFrame *frame)
 {
     int ret;
 
+    // make sure there is no aliasing in the following switch
+    if (s->bpp >= 100 || s->bppcount >= 10) {
+        av_log(s->avctx, AV_LOG_ERROR,
+               "Unsupported image parameters: bpp=%d, bppcount=%d\n",
+               s->bpp, s->bppcount);
+        return AVERROR_INVALIDDATA;
+    }
+
     switch (s->planar * 1000 + s->bpp * 10 + s->bppcount) {
     case 11:
         s->avctx->pix_fmt = AV_PIX_FMT_MONOBLACK;