lavc/pngdec: improve chunk length check

elenril · elenril · commit c64180fac844 · 2021-04-08T14:15:30.000+02:00
The length does not cover the chunk type or CRC. (cherry picked from commit ae08eec) Signed-off-by: Anton Khirnov <anton@khirnov.net>
diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
@@ -1217,7 +1217,7 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
         }
 
         length = bytestream2_get_be32(&s->gb);
-        if (length > 0x7fffffff || length > bytestream2_get_bytes_left(&s->gb)) {
+        if (length > 0x7fffffff || length + 8 > bytestream2_get_bytes_left(&s->gb)) {
             av_log(avctx, AV_LOG_ERROR, "chunk too big\n");
             ret = AVERROR_INVALIDDATA;
             goto fail;

Original file line number	Diff line number	Diff line change
`@@ -1217,7 +1217,7 @@ static int decode_frame_common(AVCodecContext avctx, PNGDecContext s,`
`1217`	`1217`	`}`
`1218`	`1218`
`1219`	`1219`	`length = bytestream2_get_be32(&s->gb);`
`1220`		`- if (length > 0x7fffffff \|\| length > bytestream2_get_bytes_left(&s->gb)) {`
	`1220`	`+ if (length > 0x7fffffff \|\| length + 8 > bytestream2_get_bytes_left(&s->gb)) {`
`1221`	`1221`	`av_log(avctx, AV_LOG_ERROR, "chunk too big\n");`
`1222`	`1222`	`ret = AVERROR_INVALIDDATA;`
`1223`	`1223`	`goto fail;`