Referring to
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=60379
there are some specially-crafted malformed JPEG images that, when
transformed to grayscale, will exceed the worst-case transformed
grayscale JPEG image size. This is similar in nature to the issue fixed
by c8d52f1c4c, except that in this case,
the issue occurs regardless of the amount of metadata in the source
image. Also, the tj3Transform() function, the
Java_org_libjpegturbo_turbojpeg_TJTransformer_transform() JNI function,
and TJBench were behaving correctly in this case, because the TurboJPEG
API documentation specifies that the source image's subsampling type
should be used when computing the worst-case transformed JPEG image
size. (However, only the Java API documentation specified that. Oops.
The C API documentation now does as well.) The documented usage
mitigates the issue, and only the transform fuzzer did not adhere to
that. Thus, this was an issue with the fuzzer itself rather than an
issue with the library.
895287572d
