Re: [FFmpeg-devel] [PATCH] avcodec/dpx: fix check of minimal data size for unpadded content

[Jerome Martinez <jerome@mediaarea.net>]

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Please consider the attached patch.

Before: "Overread buffer. Invalid header?" despite that all bytes are 
there (the precheck is wrong, not the parsing after the precheck)
After: transcoding is fine

A (zeroed) sample file is available at https://trac.ffmpeg.org/ticket/10259

Jérôme

On 19/10/2022 11:47, Jerome Martinez wrote:
> stride value is not relevant with unpadded content and the total count 
> of pixels (width x height) must be used instead of the rounding based 
> on width only then multiplied by height
>
> unpadded_10bit value computing is moved sooner in the code in order to 
> be able to use it during computing of minimal content size
>
> Fix 'Overread buffer' error when the content is not lucky enough to 
> have (enough) padding bytes at the end for not being rejected by the 
> formula based on the stride value
>
> Signed-off-by: Jerome Martinez <jerome@mediaarea.net>
> ---
>  libavcodec/dpx.c | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/libavcodec/dpx.c b/libavcodec/dpx.c
> index 4f50608..d4699f6 100644
> --- a/libavcodec/dpx.c
> +++ b/libavcodec/dpx.c
> @@ -476,14 +476,30 @@ static int decode_frame(AVCodecContext *avctx, 
> AVFrame *p,
>          avctx->colorspace = AVCOL_SPC_RGB;
>      }
>
> +    av_strlcpy(creator, avpkt->data + 160, 100);
> +    creator[100] = '\0';
> +    av_dict_set(&p->metadata, "Creator", creator, 0);
> +
> +    av_strlcpy(input_device, avpkt->data + 1556, 32);
> +    input_device[32] = '\0';
> +    av_dict_set(&p->metadata, "Input Device", input_device, 0);
> +
> +    // Some devices do not pad 10bit samples to whole 32bit words per 
> row
> +    if (!memcmp(input_device, "Scanity", 7) ||
> +        !memcmp(creator, "Lasergraphics Inc.", 18)) {
> +        unpadded_10bit = 1;
> +    }
> +
>      // Table 3c: Runs will always break at scan line boundaries. Packing
>      // will always break to the next 32-bit word at scan-line 
> boundaries.
>      // Unfortunately, the encoder produced invalid files, so attempt
>      // to detect it
> +    // Also handle special case with unpadded content
>      need_align = FFALIGN(stride, 4);
> -    if (need_align*avctx->height + (int64_t)offset > avpkt->size) {
> +    if (need_align*avctx->height + (int64_t)offset > avpkt->size &&
> +        (!unpadded_10bit || (avctx->width * avctx->height * elements 
> + 2) / 3 * 4 + (int64_t)offset > avpkt->size)) {
>          // Alignment seems unappliable, try without
> -        if (stride*avctx->height + (int64_t)offset > avpkt->size) {
> +        if (stride*avctx->height + (int64_t)offset > avpkt->size || 
> unpadded_10bit) {
>              av_log(avctx, AV_LOG_ERROR, "Overread buffer. Invalid 
> header?\n");
>              return AVERROR_INVALIDDATA;
>          } else {
> @@ -609,20 +625,6 @@ static int decode_frame(AVCodecContext *avctx, 
> AVFrame *p,
>      if ((ret = ff_get_buffer(avctx, p, 0)) < 0)
>          return ret;
>
> -    av_strlcpy(creator, avpkt->data + 160, 100);
> -    creator[100] = '\0';
> -    av_dict_set(&p->metadata, "Creator", creator, 0);
> -
> -    av_strlcpy(input_device, avpkt->data + 1556, 32);
> -    input_device[32] = '\0';
> -    av_dict_set(&p->metadata, "Input Device", input_device, 0);
> -
> -    // Some devices do not pad 10bit samples to whole 32bit words per 
> row
> -    if (!memcmp(input_device, "Scanity", 7) ||
> -        !memcmp(creator, "Lasergraphics Inc.", 18)) {
> -        unpadded_10bit = 1;
> -    }
> -
>      // Move pointer to offset from start of file
>      buf =  avpkt->data + offset;
>

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From 21c21373ca576f1dff05f952c17275957b9388bd Mon Sep 17 00:00:00 2001
From: Jerome Martinez <jerome@mediaarea.net>
Date: Wed, 19 Oct 2022 11:37:34 +0200
Subject: [PATCH] avcodec/dpx: fix check of minimal data size for unpadded
 content

stride value is not relevant with unpadded content and the total count of pixels (width x height) must be used instead of the rounding based on width only then multiplied by height

unpadded_10bit value computing is moved sooner in the code in order to be able to use it during computing of minimal content size

Fix 'Overread buffer' error when the content is not lucky enough to have (enough) padding bytes at the end for not being rejected by the formula based on the stride value
---
 libavcodec/dpx.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/libavcodec/dpx.c b/libavcodec/dpx.c
index 4f50608461..d4699f65fc 100644
--- a/libavcodec/dpx.c
+++ b/libavcodec/dpx.c
@@ -476,14 +476,30 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *p,
         avctx->colorspace = AVCOL_SPC_RGB;
     }
 
+    av_strlcpy(creator, avpkt->data + 160, 100);
+    creator[100] = '\0';
+    av_dict_set(&p->metadata, "Creator", creator, 0);
+
+    av_strlcpy(input_device, avpkt->data + 1556, 32);
+    input_device[32] = '\0';
+    av_dict_set(&p->metadata, "Input Device", input_device, 0);
+
+    // Some devices do not pad 10bit samples to whole 32bit words per row
+    if (!memcmp(input_device, "Scanity", 7) ||
+        !memcmp(creator, "Lasergraphics Inc.", 18)) {
+        unpadded_10bit = 1;
+    }
+
     // Table 3c: Runs will always break at scan line boundaries. Packing
     // will always break to the next 32-bit word at scan-line boundaries.
     // Unfortunately, the encoder produced invalid files, so attempt
     // to detect it
+    // Also handle special case with unpadded content
     need_align = FFALIGN(stride, 4);
-    if (need_align*avctx->height + (int64_t)offset > avpkt->size) {
+    if (need_align*avctx->height + (int64_t)offset > avpkt->size &&
+        (!unpadded_10bit || (avctx->width * avctx->height * elements + 2) / 3 * 4 + (int64_t)offset > avpkt->size)) {
         // Alignment seems unappliable, try without
-        if (stride*avctx->height + (int64_t)offset > avpkt->size) {
+        if (stride*avctx->height + (int64_t)offset > avpkt->size || unpadded_10bit) {
             av_log(avctx, AV_LOG_ERROR, "Overread buffer. Invalid header?\n");
             return AVERROR_INVALIDDATA;
         } else {
@@ -609,20 +625,6 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *p,
     if ((ret = ff_get_buffer(avctx, p, 0)) < 0)
         return ret;
 
-    av_strlcpy(creator, avpkt->data + 160, 100);
-    creator[100] = '\0';
-    av_dict_set(&p->metadata, "Creator", creator, 0);
-
-    av_strlcpy(input_device, avpkt->data + 1556, 32);
-    input_device[32] = '\0';
-    av_dict_set(&p->metadata, "Input Device", input_device, 0);
-
-    // Some devices do not pad 10bit samples to whole 32bit words per row
-    if (!memcmp(input_device, "Scanity", 7) ||
-        !memcmp(creator, "Lasergraphics Inc.", 18)) {
-        unpadded_10bit = 1;
-    }
-
     // Move pointer to offset from start of file
     buf =  avpkt->data + offset;
 
-- 
2.13.3.windows.1


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