Due to incorrect use of integer types and missing overflow checks in
the tre_tnfa_run_parallel function's buffer overflow logic, the TRE
regex implementation (both original version and the one used in musl
libc) are subject to integer overflows in buffer size computation.

If the caller passes to regcomp a regular expression whose internal
representation requires a large number of states and/or a large number
of tags, too little space will be allocated during regexec, resulting
in out-of-bound memory writes.

An attacker who controls the regular expression and/or the string
being searched can potentially exploit these writes to achieve
controlled heap corruption.

All versions of the TRE library and musl libc are affected. The
attached patch fixes the issue in musl and should be easy to adapt for
use with original TRE. musl git master is fixed as of commit
c3edc06d1e1360f3570db9155d6b318ae0d0f0f7.

Rich