[FFmpeg-devel] [PATCH] avformat/mov: (v2) fix get_eia608_packet

* [FFmpeg-devel] [PATCH] avformat/mov: (v2) fix get_eia608_packet
@ 2025-02-13 17:55 Pavel Koshevoy
  2025-02-13 21:04 ` Pavel Koshevoy
  0 siblings, 1 reply; 2+ messages in thread
From: Pavel Koshevoy @ 2025-02-13 17:55 UTC (permalink / raw)
  To: ffmpeg-devel; +Cc: Pavel Koshevoy

The problem is reproducible with "Test for Quicktime 608 CC file.mov"
from https://samples.ffmpeg.org/MPEG2/subcc/

ffmpeg_g -i "Test for Quicktime 608 CC file.mov" -map 0 -c copy -y remuxed.mov

Prior to the fix QuickTime Player playback of remuxed.mov would
render cdt2 atom type tags as part of "English CC" subtitles.
---
 libavformat/mov.c | 54 +++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 45 insertions(+), 9 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 85aef33b19..65b4f3dd5c 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -10790,22 +10790,58 @@ static int mov_change_extradata(AVStream *st, AVPacket *pkt)
 
 static int get_eia608_packet(AVIOContext *pb, AVPacket *pkt, int size)
 {
-    int new_size, ret;
+    /* We can't make assumptions about the structure of the payload,
+       because it may include multiple cdat and cdt2 samples. */
+    int ret, out_size_max, out_size = 0;
 
-    if (size <= 8)
+    /* a valide payload must have size, 4cc, and at least 1 byte pair: */
+    if (size <= 10 || size % 2 != 0)
         return AVERROR_INVALIDDATA;
-    new_size = ((size - 8) / 2) * 3;
-    ret = av_new_packet(pkt, new_size);
+
+    /* avoid an int overflow: */
+    if ((size - 8) / 2 >= (INT_MAX - size) / 3)
+        return AVERROR_INVALIDDATA;
+
+    /* Allocate the buffer larger enough to store the output cc_data_pkts
+       and the original c608 payload, safely. */
+    out_size_max = ((size - 8) / 2) * 3;
+    ret = av_new_packet(pkt, out_size_max + size);
     if (ret < 0)
         return ret;
 
-    avio_skip(pb, 8);
-    for (int j = 0; j < new_size; j += 3) {
-        pkt->data[j] = 0xFC;
-        pkt->data[j+1] = avio_r8(pb);
-        pkt->data[j+2] = avio_r8(pb);
+    /* Load the original c608 payload into the last 3rd of the buffer. */
+    if (avio_read(pb, pkt->data + out_size_max, size) != size)
+        return AVERROR_EOF;
+
+    /* parse and re-format the c608 payload in one pass. */
+    for (uint8_t *out = pkt->data, *src = out + out_size_max, *end = src + size; src + 8 <= end; ) {
+        uint32_t atom_size = AV_RB32(src);
+        uint8_t cc_field =
+            memcmp(src + 4, "cdat", 4) == 0 ? 1 :
+            memcmp(src + 4, "cdt2", 4) == 0 ? 2 :
+            0;
+
+        /* make sure the atom size stays within the buffer boundaries. */
+        if (src + atom_size > end)
+            return AVERROR_INVALIDDATA;
+
+        /* make sure the payload size is consistent with N byte pairs. */
+        if ((atom_size - 8) % 2 != 0)
+            return AVERROR_INVALIDDATA;
+
+        if (cc_field != 0) {
+            for (uint8_t *cc = src + 8, *cc_end = src + atom_size; cc < cc_end; cc += 2) {
+                out[0] = (0x1F << 3) | (1 << 2) | (cc_field - 1);
+                out[1] = cc[0];
+                out[2] = cc[1];
+                out_size += 3;
+                out += 3;
+            }
+        }
+        src += atom_size;
     }
 
+    av_shrink_packet(pkt, out_size);
     return 0;
 }
 
-- 
2.43.0

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