[FFmpeg-devel] [PATCH 1/2] avformat/jpegxl_probe: check length instead of blindly reading

[Michael Niedermayer]

Enable the checked bitreader to avoid overread.
Also add a few checks in loops and between blocks so we exit instead of continued
execution.
Alternatively we could add manual checks so that no overread can happen. This would be
slightly faster but a bit more work and a bit more fragile

Fixes: Out of array accesses
Fixes: 59640/clusterfuzz-testcase-minimized-ffmpeg_dem_JPEGXL_ANIM_fuzzer-6584117345779712

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavformat/jpegxl_probe.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/libavformat/jpegxl_probe.c b/libavformat/jpegxl_probe.c
index 1d9c014f19..e15e9eee49 100644
--- a/libavformat/jpegxl_probe.c
+++ b/libavformat/jpegxl_probe.c
@@ -21,6 +21,7 @@
 
 #include "jpegxl_probe.h"
 
+#define UNCHECKED_BITSTREAM_READER 0
 #define BITSTREAM_READER_LE
 #include "libavcodec/get_bits.h"
 
@@ -293,6 +294,8 @@ int ff_jpegxl_verify_codestream_header(const uint8_t *buf, int buflen, int valid
             skip_bits_long(gb, 1);
         }
     }
+    if (get_bits_left(gb) < 1)
+        return AVERROR_INVALIDDATA;
 
     if (!all_default) {
         jpegxl_skip_bit_depth(gb);
@@ -307,6 +310,8 @@ int ff_jpegxl_verify_codestream_header(const uint8_t *buf, int buflen, int valid
         for (uint32_t i = 0; i < num_extra_channels; i++) {
             if (jpegxl_read_extra_channel_info(gb, validate_level) < 0)
                 return -1;
+            if (get_bits_left(gb) < 1)
+                return AVERROR_INVALIDDATA;
         }
 
         xyb_encoded = get_bits1(gb);
@@ -336,8 +341,11 @@ int ff_jpegxl_verify_codestream_header(const uint8_t *buf, int buflen, int valid
                             return -1;
                         if (primaries == FF_JPEGXL_PR_CUSTOM) {
                             /* ux/uy values for r,g,b */
-                            for (int i = 0; i < 6; i++)
+                            for (int i = 0; i < 6; i++) {
                                 jxl_u32(gb, 0, 524288, 1048576, 2097152, 19, 19, 20, 21);
+                                if (get_bits_left(gb) < 1)
+                                    return AVERROR_INVALIDDATA;
+                            }
                         }
                     }
                 }
@@ -363,10 +371,14 @@ int ff_jpegxl_verify_codestream_header(const uint8_t *buf, int buflen, int valid
             skip_bits_long(gb, 16 + 16 + 1 + 16);
 
         extensions = jpegxl_u64(gb);
+        if (get_bits_left(gb) < 1)
+            return AVERROR_INVALIDDATA;
         if (extensions) {
             for (int i = 0; i < 64; i++) {
                 if (extensions & (UINT64_C(1) << i))
                     jpegxl_u64(gb);
+                if (get_bits_left(gb) < 1)
+                    return AVERROR_INVALIDDATA;
             }
         }
     }
-- 
2.17.1