avcodec/jpeglsdec: Don't presume the context to contain a JLSState

Before 9b3c46a081 every call to
ff_jpegls_decode_picture() allocated and freed a JLSState. This commit
instead put said structure into the context of the JPEG-LS decoder to
avoid said allocation. But said function can also be called from other
MJPEG-based decoders and their contexts doesn't contain said structure,
leading to segfaults. This commit fixes this: The JLSState is now
allocated on the first call to ff_jpegls_decode_picture() and stored in
the context.

Found-by: Michael Niedermayer <michael@niedermayer.cc>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/jpeglsdec.c

@@ -45,11 +45,6 @@
  */
 //#define JLS_BROKEN
 
-typedef struct JpegLSDecodeContext {
-    MJpegDecodeContext mjpeg;
-    JLSState state;
-} JpegLSDecodeContext;
-
 /**
  * Decode LSE block with initialization parameters
  */
@@ -355,10 +350,16 @@ int ff_jpegls_decode_picture(MJpegDecodeContext *s, int near,
 {
     int i, t = 0;
     uint8_t *zero, *last, *cur;
-    JLSState *const state = &((JpegLSDecodeContext*)s)->state;
+    JLSState *state = s->jls_state;
     int off = 0, stride = 1, width, shift, ret = 0;
     int decoded_height = 0;
 
+    if (!state) {
+        state = av_malloc(sizeof(*state));
+        if (!state)
+            return AVERROR(ENOMEM);
+        s->jls_state = state;
+    }
     zero = av_mallocz(s->picture_ptr->linesize[0]);
     if (!zero)
         return AVERROR(ENOMEM);
@@ -548,7 +549,7 @@ AVCodec ff_jpegls_decoder = {
     .long_name      = NULL_IF_CONFIG_SMALL("JPEG-LS"),
     .type           = AVMEDIA_TYPE_VIDEO,
     .id             = AV_CODEC_ID_JPEGLS,
-    .priv_data_size = sizeof(JpegLSDecodeContext),
+    .priv_data_size = sizeof(MJpegDecodeContext),
     .init           = ff_mjpeg_decode_init,
     .close          = ff_mjpeg_decode_end,
     .receive_frame  = ff_mjpeg_receive_frame,

libavcodec/mjpegdec.c

@@ -2916,6 +2916,7 @@ av_cold int ff_mjpeg_decode_end(AVCodecContext *avctx)
     reset_icc_profile(s);
 
     av_freep(&s->hwaccel_picture_private);
+    av_freep(&s->jls_state);
 
     return 0;
 }

libavcodec/mjpegdec.h

@@ -49,6 +49,8 @@ typedef struct ICCEntry {
     int    length;
 } ICCEntry;
 
+struct JLSState;
+
 typedef struct MJpegDecodeContext {
     AVClass *class;
     AVCodecContext *avctx;
@@ -163,6 +165,7 @@ typedef struct MJpegDecodeContext {
     enum AVPixelFormat hwaccel_sw_pix_fmt;
     enum AVPixelFormat hwaccel_pix_fmt;
     void *hwaccel_picture_private;
+    struct JLSState *jls_state;
 } MJpegDecodeContext;
 
 int ff_mjpeg_build_vlc(VLC *vlc, const uint8_t *bits_table,