[FFmpeg-devel] pngdec: add ability to check chunk CRC

Submitted by Lynne on March 7, 2019, 6:26 p.m.

Details

Message ID L_OP1bH--3-1@lynne.ee
State New
Headers show

Commit Message

Lynne March 7, 2019, 6:26 p.m.
By default now, if AV_EF_CRCCHECK or AV_EF_IGNORE_ERR are enabled the decoder
will skip the chunk and carry on with the next one. This should make the       
decoder able to decode more corrupt files because the functions which decode
individual chunks will very likely error out if fed invalid data and stop the
decoding of the entire image.
Should this be made default? CRC verification doesn't take long even for very
large files.                                                      
Also fix the length check for chunk size. It needs to take into account the
4 byte tag as well as the 4 byte CRC.

Comments

Michael Niedermayer March 7, 2019, 9:22 p.m.
On Thu, Mar 07, 2019 at 07:26:32PM +0100, Lynne wrote:
> By default now, if AV_EF_CRCCHECK or AV_EF_IGNORE_ERR are enabled the decoder
> will skip the chunk and carry on with the next one. This should make the       
> decoder able to decode more corrupt files because the functions which decode
> individual chunks will very likely error out if fed invalid data and stop the
> decoding of the entire image.
> Should this be made default? CRC verification doesn't take long even for very
> large files.                                                      
> Also fix the length check for chunk size. It needs to take into account the
> 4 byte tag as well as the 4 byte CRC.
> 

>  pngdec.c |   19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 4255c91468cee2bc2fa757fae69762ff5ee5774a  0001-pngdec-add-ability-to-check-chunk-CRC.patch
> From 7aff99d12faf557753c5ee860a9672c7a09a26e3 Mon Sep 17 00:00:00 2001
> From: Lynne <dev@lynne.ee>
> Date: Thu, 7 Mar 2019 18:15:23 +0000
> Subject: [PATCH] pngdec: add ability to check chunk CRC
> 
> By default now, if AV_EF_CRCCHECK or AV_EF_IGNORE_ERR are enabled the decoder
> will skip the chunk and carry on with the next one. This should make the
> decoder able to decode more corrupt files because the functions which decode
> individual chunks will very likely error out if fed invalid data and stop the
> decoding of the entire image.
> Should this be made default? CRC verification doesn't take long even for very
> large files.

i would tend toward enabling it by default but maybe first post some
numbers of how much this changes decode time 


> Also fix the length check for chunk size. It needs to take into account the
> 4 byte tag as well as the 4 byte CRC.

this should be a seperate patch as its unrelated

thx

[...]
Lynne March 17, 2019, 1:30 p.m.
8 Mar 2019, 14:15 by dev@lynne.ee:

> 7 Mar 2019, 21:22 by > michael@niedermayer.cc <mailto:michael@niedermayer.cc>> :
>
>> On Thu, Mar 07, 2019 at 07:26:32PM +0100, Lynne wrote:
>>
>>> By default now, if AV_EF_CRCCHECK or AV_EF_IGNORE_ERR are enabled the decoder
>>> will skip the chunk and carry on with the next one. This should make the       
>>> decoder able to decode more corrupt files because the functions which decode
>>> individual chunks will very likely error out if fed invalid data and stop the
>>> decoding of the entire image.
>>> Should this be made default? CRC verification doesn't take long even for very
>>> large files.                                                      
>>> Also fix the length check for chunk size. It needs to take into account the
>>> 4 byte tag as well as the 4 byte CRC.
>>>
>>> pngdec.c |   19 ++++++++++++++++++-
>>>  1 file changed, 18 insertions(+), 1 deletion(-)
>>> 4255c91468cee2bc2fa757fae69762ff5ee5774a  0001-pngdec-add-ability-to-check-chunk-CRC.patch
>>> From 7aff99d12faf557753c5ee860a9672c7a09a26e3 Mon Sep 17 00:00:00 2001
>>> From: Lynne <>> >>> dev@lynne.ee <mailto:dev@lynne.ee>>>>  <mailto:>>> dev@lynne.ee <mailto:dev@lynne.ee>>>> >>> >
>>> Date: Thu, 7 Mar 2019 18:15:23 +0000
>>> Subject: [PATCH] pngdec: add ability to check chunk CRC
>>>
>>> By default now, if AV_EF_CRCCHECK or AV_EF_IGNORE_ERR are enabled the decoder
>>> will skip the chunk and carry on with the next one. This should make the
>>> decoder able to decode more corrupt files because the functions which decode
>>> individual chunks will very likely error out if fed invalid data and stop the
>>> decoding of the entire image.
>>> Should this be made default? CRC verification doesn't take long even for very
>>> large files.
>>>
>>
>> i would tend toward enabling it by default but maybe first post some
>> numbers of how much this changes decode time 
>>
>
> For the largest png I found: > https://vk.com/doc218587497_437472325?hash=51300ca9ba40f462ac&dl=1bcf9a57b0d989da1f <https://vk.com/doc218587497_437472325?hash=51300ca9ba40f462ac&dl=1bcf9a57b0d989da1f>>  <> https://vk.com/doc218587497_437472325?hash=51300ca9ba40f462ac&dl=1bcf9a57b0d989da1f <https://vk.com/doc218587497_437472325?hash=51300ca9ba40f462ac&dl=1bcf9a57b0d989da1f>> >
>
> There was no increase in decoding time, it took 2.3 seconds on my machine
> with and without -err_detect crccheck.
>
> With -err_detect crccheck perf reported 2.52% spent in av_crc
>
>
>>> Also fix the length check for chunk size. It needs to take into account the
>>> 4 byte tag as well as the 4 byte CRC.
>>>
>>
>> this should be a seperate patch as its unrelated
>>
>
> removed and attached new patch file
>
> Maybe always enabling the CRC check isn't worth it since if you download from
> the internet you could either get a full error-free file or an incomplete one
> rather than a corrupt one. Maybe only for torrents with huge png files where
> not all chunks have been downloaded yet, or broken hard drives, but the ignore_err
> flag could be manually enabled in those cases.
>

Ping? The apedec CRC patch needs a review too.

Patch hide | download patch | download mbox

From 7aff99d12faf557753c5ee860a9672c7a09a26e3 Mon Sep 17 00:00:00 2001
From: Lynne <dev@lynne.ee>
Date: Thu, 7 Mar 2019 18:15:23 +0000
Subject: [PATCH] pngdec: add ability to check chunk CRC

By default now, if AV_EF_CRCCHECK or AV_EF_IGNORE_ERR are enabled the decoder
will skip the chunk and carry on with the next one. This should make the
decoder able to decode more corrupt files because the functions which decode
individual chunks will very likely error out if fed invalid data and stop the
decoding of the entire image.
Should this be made default? CRC verification doesn't take long even for very
large files.
Also fix the length check for chunk size. It needs to take into account the
4 byte tag as well as the 4 byte CRC.
---
 libavcodec/pngdec.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 189bb9a4c1..30b6dc3166 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -23,6 +23,7 @@ 
 
 #include "libavutil/avassert.h"
 #include "libavutil/bprint.h"
+#include "libavutil/crc.h"
 #include "libavutil/imgutils.h"
 #include "libavutil/stereo3d.h"
 #include "libavutil/mastering_display_metadata.h"
@@ -1169,6 +1170,7 @@  static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
 static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
                                AVFrame *p, AVPacket *avpkt)
 {
+    const AVCRC *crc_tab = av_crc_get_table(AV_CRC_32_IEEE_LE);
     AVDictionary **metadatap = NULL;
     uint32_t tag, length;
     int decode_next_dat = 0;
@@ -1198,11 +1200,26 @@  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;
         }
+        if (avctx->err_recognition & (AV_EF_CRCCHECK | AV_EF_IGNORE_ERR)) {
+            uint32_t crc_sig = AV_RB32(s->gb.buffer + length + 4);
+            uint32_t crc_cal = ~av_crc(crc_tab, UINT32_MAX, s->gb.buffer, length + 4);
+            if (crc_sig ^ crc_cal) {
+                av_log(avctx, AV_LOG_ERROR, "CRC mismatch in chunk");
+                if (avctx->err_recognition & AV_EF_EXPLODE) {
+                    av_log(avctx, AV_LOG_ERROR, ", quitting\n");
+                    ret = AVERROR_INVALIDDATA;
+                    goto fail;
+                }
+                av_log(avctx, AV_LOG_ERROR, ", skipping\n");
+                bytestream2_skip(&s->gb, 4); /* tag */
+                goto skip_tag;
+            }
+        }
         tag = bytestream2_get_le32(&s->gb);
         if (avctx->debug & FF_DEBUG_STARTCODE)
             av_log(avctx, AV_LOG_DEBUG, "png: tag=%s length=%u\n",
-- 
2.21.0