[FFmpeg-devel] [PATCH 1/2] avcodec/av1_parse: take trailing bits into account when initializing the GetBitContext

[James Almer]

Also only initialize it in ff_av1_packet_split() and not ff_av1_extract_obu(),
same as h2645_parse, so GetBitContext specific failures may not affect the
former.

Signed-off-by: James Almer <jamrial at gmail.com>
---
 libavcodec/av1_parse.c | 25 +++++++++++++++----------
 libavcodec/av1_parse.h | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 10 deletions(-)

diff --git a/libavcodec/av1_parse.c b/libavcodec/av1_parse.c
index 50dd940f03..cdd524baa8 100644
--- a/libavcodec/av1_parse.c
+++ b/libavcodec/av1_parse.c
@@ -22,6 +22,7 @@
 
 #include "libavutil/mem.h"
 
+#include "av1.h"
 #include "av1_parse.h"
 #include "bytestream.h"
 
@@ -29,16 +30,13 @@ int ff_av1_extract_obu(AV1OBU *obu, const uint8_t *buf, int length, void *logctx
 {
     int64_t obu_size;
     int start_pos, type, temporal_id, spatial_id;
-    int len, ret;
+    int len;
 
     len = parse_obu_header(buf, length, &obu_size, &start_pos,
                            &type, &temporal_id, &spatial_id);
     if (len < 0)
         return len;
 
-    if (obu_size > INT_MAX / 8 || obu_size < 0)
-        return AVERROR(ERANGE);
-
     obu->type        = type;
     obu->temporal_id = temporal_id;
     obu->spatial_id  = spatial_id;
@@ -48,10 +46,6 @@ int ff_av1_extract_obu(AV1OBU *obu, const uint8_t *buf, int length, void *logctx
     obu->raw_data = buf;
     obu->raw_size = len;
 
-    ret = init_get_bits(&obu->gb, obu->data, obu->size * 8);
-    if (ret < 0)
-        return ret;
-
     av_log(logctx, AV_LOG_DEBUG,
            "obu_type: %d, temporal_id: %d, spatial_id: %d, payload size: %d\n",
            obu->type, obu->temporal_id, obu->spatial_id, obu->size);
@@ -62,7 +56,7 @@ int ff_av1_extract_obu(AV1OBU *obu, const uint8_t *buf, int length, void *logctx
 int ff_av1_packet_split(AV1Packet *pkt, const uint8_t *buf, int length, void *logctx)
 {
     GetByteContext bc;
-    int consumed;
+    int ret, consumed;
 
     bytestream2_init(&bc, buf, length);
     pkt->nb_obus = 0;
@@ -87,9 +81,20 @@ int ff_av1_packet_split(AV1Packet *pkt, const uint8_t *buf, int length, void *lo
         if (consumed < 0)
             return consumed;
 
+        bytestream2_skip(&bc, consumed);
+
+        obu->size_bits = get_obu_bit_length(obu->data, obu->size, obu->type);
+
+        if (obu->size_bits < 0 || (!obu->size_bits && obu->type != AV1_OBU_TEMPORAL_DELIMITER)) {
+            av_log(logctx, AV_LOG_ERROR, "Invalid OBU of type %d, skipping.\n", obu->type);
+            continue;
+        }
+
         pkt->nb_obus++;
 
-        bytestream2_skip(&bc, consumed);
+        ret = init_get_bits(&obu->gb, obu->data, obu->size_bits);
+        if (ret < 0)
+            return ret;
     }
 
     return 0;
diff --git a/libavcodec/av1_parse.h b/libavcodec/av1_parse.h
index 9a6e6835ab..0de619dbec 100644
--- a/libavcodec/av1_parse.h
+++ b/libavcodec/av1_parse.h
@@ -23,6 +23,7 @@
 
 #include <stdint.h>
 
+#include "av1.h"
 #include "avcodec.h"
 #include "get_bits.h"
 
@@ -31,6 +32,12 @@ typedef struct AV1OBU {
     int size;
     const uint8_t *data;
 
+    /**
+     * Size, in bits, of just the data, excluding the trailing_one_bit and
+     * any trailing padding.
+     */
+    int size_bits;
+
     /** Size of entire OBU, including header */
     int raw_size;
     const uint8_t *raw_data;
@@ -133,4 +140,35 @@ static inline int parse_obu_header(const uint8_t *buf, int buf_size,
     return size;
 }
 
+static inline int get_obu_bit_length(const uint8_t *buf, int size, int type)
+{
+    int v;
+
+    /* There are no trailing bits on these */
+    if (type == AV1_OBU_TILE_GROUP || type == AV1_OBU_FRAME) {
+        if (size > INT_MAX / 8)
+            return AVERROR(ERANGE);
+        else
+            return size * 8;
+    }
+
+    while (size > 0 && buf[size - 1] == 0)
+        size--;
+
+    if (!size)
+        return 0;
+
+    v = buf[size - 1];
+
+    if (size > INT_MAX / 8)
+        return AVERROR(ERANGE);
+    size *= 8;
+
+    /* Remove the trailing_one_bit and following trailing zeros */
+    if (v)
+        size -= ff_ctz(v) + 1;
+
+    return size;
+}
+
 #endif /* AVCODEC_AV1_PARSE_H */
-- 
2.18.0