[FFmpeg-devel] [PATCH v4] avcodec/cbs_vp8: Use little endian in fixed() and improve the pos check

[Dai, Jianhui J]

This commit adds value range checks to cbs_vp8_read_unsigned_le,
migrates fixed() to use it, and enforces little-endian consistency for
all read methods.

The VP8 compressed header may not be byte-aligned due to boolean coding.
Use bitwise comparison to prevent the potential overread.

TETS: ffmpeg -i fate-suite/vp8-test-vectors-r1/* -vcodec copy -bsf:v
trace_headers -f null -

Signed-off-by: Jianhui Dai <jianhui.j.dai at intel.com>
---
 libavcodec/cbs_vp8.c | 53 +++++++++++++++++++++++++++++++-------------
 1 file changed, 37 insertions(+), 16 deletions(-)

diff --git a/libavcodec/cbs_vp8.c b/libavcodec/cbs_vp8.c
index 065156c248..338d56ed7f 100644
--- a/libavcodec/cbs_vp8.c
+++ b/libavcodec/cbs_vp8.c
@@ -33,22 +33,22 @@ extern const uint8_t ff_vp8_token_update_probs[4][8][3][11];
 typedef struct CBSVP8BoolDecoder {
     GetBitContext *gbc;
 
-    uint8_t value;
     uint8_t range;
 
-    uint8_t count; // Store the number of bits in the `value` buffer.
-
+    uint8_t value;
+    // Store the number of bits in the `value` buffer.
+    uint8_t count;
 } CBSVP8BoolDecoder;
 
-static int cbs_vp8_bool_decoder_init(CBSVP8BoolDecoder *decoder, GetBitContext *gbc)
+static int cbs_vp8_bool_decoder_init(CBSVP8BoolDecoder *decoder,
+                                     GetBitContext *gbc)
 {
     av_assert0(decoder);
     av_assert0(gbc);
 
     decoder->gbc = gbc;
-    decoder->value = 0;
     decoder->range = 255;
-
+    decoder->value = 0;
     decoder->count = 0;
 
     return 0;
@@ -60,7 +60,7 @@ static bool cbs_vp8_bool_decoder_fill_value(CBSVP8BoolDecoder *decoder)
 
     av_assert0(decoder->count <= 8);
     if (decoder->count == 8) {
-      return true;
+        return true;
     }
 
     if (get_bits_left(decoder->gbc) >= bits) {
@@ -141,7 +141,7 @@ static int cbs_vp8_bool_decoder_read_unsigned(
     }
 
     if (trace_enable) {
-      CBS_TRACE_READ_END();
+        CBS_TRACE_READ_END();
     }
 
     *write_to = value;
@@ -181,9 +181,11 @@ static int cbs_vp8_bool_decoder_read_signed(
     return 0;
 }
 
-static int cbs_vp8_read_unsigned_le(CodedBitstreamContext *ctx, GetBitContext *gbc,
-                                 int width, const char *name,
-                                 const int *subscripts, uint32_t *write_to)
+static int cbs_vp8_read_unsigned_le(CodedBitstreamContext *ctx,
+                                    GetBitContext *gbc, int width,
+                                    const char *name, const int *subscripts,
+                                    uint32_t *write_to, uint32_t range_min,
+                                    uint32_t range_max)
 {
     int32_t value;
 
@@ -200,6 +202,14 @@ static int cbs_vp8_read_unsigned_le(CodedBitstreamContext *ctx, GetBitContext *g
 
     CBS_TRACE_READ_END();
 
+    if (value < range_min || value > range_max) {
+        av_log(ctx->log_ctx, AV_LOG_ERROR,
+               "%s out of range: "
+               "%" PRIu32 ", but must be in [%" PRIu32 ",%" PRIu32 "].\n",
+               name, value, range_min, range_max);
+        return AVERROR_INVALIDDATA;
+    }
+
     *write_to = value;
     return 0;
 }
@@ -246,15 +256,16 @@ static int cbs_vp8_read_unsigned_le(CodedBitstreamContext *ctx, GetBitContext *g
     do { \
         uint32_t value; \
         CHECK(cbs_vp8_read_unsigned_le(ctx, rw, width, #name, \
-                                    SUBSCRIPTS(subs, __VA_ARGS__), &value)); \
+                                       SUBSCRIPTS(subs, __VA_ARGS__), &value, \
+                                       0, MAX_UINT_BITS(width))); \
         current->name = value; \
     } while (0)
 
 #define fixed(width, name, value) \
     do { \
         uint32_t fixed_value; \
-        CHECK(ff_cbs_read_unsigned(ctx, rw, width, #name, 0, &fixed_value, \
-                                   value, value)); \
+        CHECK(cbs_vp8_read_unsigned_le(ctx, rw, width, #name, 0, &fixed_value, \
+                                       value, value)); \
     } while (0)
 
 #define bc_unsigned_subs(width, prob, enable_trace, name, subs, ...) \
@@ -277,6 +288,15 @@ static int cbs_vp8_read_unsigned_le(CodedBitstreamContext *ctx, GetBitContext *g
 
 #include "cbs_vp8_syntax_template.c"
 
+#undef READ
+#undef READWRITE
+#undef RWContext
+#undef CBSVP8BoolCodingRW
+#undef xf
+#undef fixed
+#undef bc_unsigned_subs
+#undef bc_signed_subs
+
 static int cbs_vp8_split_fragment(CodedBitstreamContext *ctx,
                                   CodedBitstreamFragment *frag, int header)
 {
@@ -327,9 +347,10 @@ static int cbs_vp8_read_unit(CodedBitstreamContext *ctx,
     if (err < 0)
         return err;
 
+    // Position may not be byte-aligned after compressed header; use bit-level
+    // comparison.
     pos = get_bits_count(&gbc);
-    pos /= 8;
-    av_assert0(pos <= unit->data_size);
+    av_assert0(pos <= unit->data_size * 8);
 
     frame->data_ref = av_buffer_ref(unit->data_ref);
     if (!frame->data_ref)
-- 
2.25.1