0 byte write heap buffer overflow in start_decoder in stb_vorbis

Vulnerability Description

stb_vorbis is a single file MIT licensed library for processing ogg vorbis files. A crafted file may trigger out of bounds write in `f->vendor[len] = (char)'\0';`. The root cause is that if the len read in `start_decoder` is `-1` and `len + 1` becomes 0 when passed to `setup_malloc`. The `setup_malloc` behaves differently when `f->alloc.alloc_buffer` is pre-allocated. Instead of returning `NULL` as in `malloc` case it shifts the pre-allocated buffer by zero and returns the currently available memory block. This issue may lead to code execution.

References

• https://securitylab.github.com/advisories/GHSL-2023-145_GHSL-2023-151_stb_image_h/
• https://github.com/nothings/stb/blob/5736b15f7ea0ffb08dd38af21067c314d6a3aae9/stb_vorbis.c#L3652-L3658
• https://github.com/nothings/stb/blob/5736b15f7ea0ffb08dd38af21067c314d6a3aae9/stb_vorbis.c#L3658
• https://github.com/nothings/stb/blob/5736b15f7ea0ffb08dd38af21067c314d6a3aae9/stb_vorbis.c#L950-L960
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/UVQ7ONFH5GWLMXYEAJG32A3EUKUCEVCR/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QVABVF4GEM6BYD5L4L64RCRSXUHY6LGN/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NMXKOKPP4BKTNUTF5KSRDQAWOUILQZNO/