[FFmpeg-devel] [PATCH] avcodec/jpegxl_parser: fix OOB read regression

[FFmpeg-devel] [PATCH] avcodec/jpegxl_parser: fix OOB read regression

[Leo Izen]

In f7ac3512f5b5cb8eb149f37300b43461d8e93af3 the size of the dynamically
allocated buffer was shrunk, but it was made too small for very small
alphabet sizes. This patch sets a minimum size to prevent an OOB read.

Reported-by: Cole Dilorenzo <coolkingcole@gmail.com>
Signed-off-by: Leo Izen <leo.izen@gmail.com>
---
 libavcodec/jpegxl_parser.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/jpegxl_parser.c b/libavcodec/jpegxl_parser.c
index dde36b0d6e..e00e01e82b 100644
--- a/libavcodec/jpegxl_parser.c
+++ b/libavcodec/jpegxl_parser.c
@@ -726,8 +726,8 @@ static int read_vlc_prefix(GetBitContext *gb, JXLEntropyDecoder *dec, JXLSymbolD
     if (ret < 0)
         goto end;
 
-    buf = av_mallocz(dist->alphabet_size * (2 * sizeof(int8_t) + sizeof(int16_t) + sizeof(uint32_t))
-                     + sizeof(uint32_t));
+    buf = av_mallocz(dist->alphabet_size * (2 * sizeof(int8_t) + sizeof(int16_t))
+        + FFMAX(15, dist->alphabet_size + 1) * sizeof(uint32_t));
     if (!buf) {
         ret = AVERROR(ENOMEM);
         goto end;
-- 
2.42.0

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".

[FFmpeg-devel] [PATCH v2] avcodec/jpegxl_parser: fix OOB read regression

[Leo Izen]

In f7ac3512f5b5cb8eb149f37300b43461d8e93af3 the size of the dynamically
allocated buffer was shrunk, but it was made too small for very small
alphabet sizes. This patch restores the size to prevent an OOB read.

Reported-by: Cole Dilorenzo <coolkingcole@gmail.com>
Signed-off-by: Leo Izen <leo.izen@gmail.com>
---
 libavcodec/jpegxl_parser.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/libavcodec/jpegxl_parser.c b/libavcodec/jpegxl_parser.c
index dde36b0d6e..630fc8a60b 100644
--- a/libavcodec/jpegxl_parser.c
+++ b/libavcodec/jpegxl_parser.c
@@ -683,7 +683,7 @@ static int read_vlc_prefix(GetBitContext *gb, JXLEntropyDecoder *dec, JXLSymbolD
     int repeat_count_prev = 0, repeat_count_zero = 0, prev = 8;
     int total_code = 0, len, hskip, num_codes = 0, ret;
 
-    VLC level1_vlc;
+    VLC level1_vlc = { 0 };
 
     if (dist->alphabet_size == 1) {
         dist->vlc.bits = 0;
@@ -709,8 +709,10 @@ static int read_vlc_prefix(GetBitContext *gb, JXLEntropyDecoder *dec, JXLSymbolD
         }
     }
 
-    if (total_code != 32 && num_codes >= 2 || num_codes < 1)
-        return AVERROR_INVALIDDATA;
+    if (total_code != 32 && num_codes >= 2 || num_codes < 1) {
+        ret = AVERROR_INVALIDDATA;
+        goto end;
+    }
 
     for (int i = 1; i < 19; i++)
          level1_codecounts[i] += level1_codecounts[i - 1];
@@ -726,7 +728,7 @@ static int read_vlc_prefix(GetBitContext *gb, JXLEntropyDecoder *dec, JXLSymbolD
     if (ret < 0)
         goto end;
 
-    buf = av_mallocz(dist->alphabet_size * (2 * sizeof(int8_t) + sizeof(int16_t) + sizeof(uint32_t))
+    buf = av_mallocz(MAX_PREFIX_ALPHABET_SIZE * (2 * sizeof(int8_t) + sizeof(int16_t) + sizeof(uint32_t))
                      + sizeof(uint32_t));
     if (!buf) {
         ret = AVERROR(ENOMEM);
@@ -734,21 +736,22 @@ static int read_vlc_prefix(GetBitContext *gb, JXLEntropyDecoder *dec, JXLSymbolD
     }
 
     level2_lens = (int8_t *)buf;
-    level2_lens_s = (int8_t *)(buf + dist->alphabet_size * sizeof(int8_t));
-    level2_syms = (int16_t *)(buf + dist->alphabet_size * (2 * sizeof(int8_t)));
-    level2_codecounts = (uint32_t *)(buf + dist->alphabet_size * (2 * sizeof(int8_t) + sizeof(int16_t)));
+    level2_lens_s = (int8_t *)(buf + MAX_PREFIX_ALPHABET_SIZE * sizeof(int8_t));
+    level2_syms = (int16_t *)(buf + MAX_PREFIX_ALPHABET_SIZE * (2 * sizeof(int8_t)));
+    level2_codecounts = (uint32_t *)(buf + MAX_PREFIX_ALPHABET_SIZE * (2 * sizeof(int8_t) + sizeof(int16_t)));
 
     total_code = 0;
     for (int i = 0; i < dist->alphabet_size; i++) {
         len = get_vlc2(gb, level1_vlc.table, 5, 1);
+        if (get_bits_left(gb) < 0) {
+            ret = AVERROR_BUFFER_TOO_SMALL;
+            goto end;
+        }
         if (len == 16) {
             int extra = 3 + get_bits(gb, 2);
             if (repeat_count_prev)
-                extra = 4 * (repeat_count_prev - 2) - repeat_count_prev + extra;
-            if (i + extra > dist->alphabet_size) {
-                ret = AVERROR_INVALIDDATA;
-                goto end;
-            }
+                extra += 4 * (repeat_count_prev - 2) - repeat_count_prev;
+            extra = FFMIN(extra, dist->alphabet_size - i);
             for (int j = 0; j < extra; j++)
                 level2_lens[i + j] = prev;
             total_code += (32768 >> prev) * extra;
@@ -759,7 +762,8 @@ static int read_vlc_prefix(GetBitContext *gb, JXLEntropyDecoder *dec, JXLSymbolD
         } else if (len == 17) {
             int extra = 3 + get_bits(gb, 3);
             if (repeat_count_zero > 0)
-                extra = 8 * (repeat_count_zero - 2) - repeat_count_zero + extra;
+                extra += 8 * (repeat_count_zero - 2) - repeat_count_zero;
+            extra = FFMIN(extra, dist->alphabet_size - i);
             i += extra - 1;
             repeat_count_prev = 0;
             repeat_count_zero += extra;
-- 
2.42.0

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-devel] [PATCH v2] avcodec/jpegxl_parser: fix OOB read regression

[Leo Izen]

On 10/14/23 20:49, Leo Izen wrote:
> In f7ac3512f5b5cb8eb149f37300b43461d8e93af3 the size of the dynamically
> allocated buffer was shrunk, but it was made too small for very small
> alphabet sizes. This patch restores the size to prevent an OOB read.
> 
> Reported-by: Cole Dilorenzo <coolkingcole@gmail.com>
> Signed-off-by: Leo Izen <leo.izen@gmail.com>
> ---

Will push soon as it fixes a fuzzer case.

- Leo Izen

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".