regexp/syntax: limit memory used by parsing regexps

[julieqiu]

The parsed regexp representation is linear in the size of the input,
but in some cases the constant factor can be as high as 40,000,
making relatively small regexps consume much larger amounts of memory.

Each regexp being parsed is now limited to a 256 MB memory footprint.
Regular expressions whose representation would use more space than that
are now rejected. Normal use of regular expressions is unaffected.

Thanks to Adam Korczynski (ADA Logics) and OSS-Fuzz for reporting this issue.

This is CVE-2022-41715 and Go issue https://go.dev/issue/55949.

[julieqiu]

@gopherbot please open backport issues.

[gopherbot]

Backport issue(s) opened: #55950 (for 1.18), #55951 (for 1.19).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[dmitshur]

Moving to Go1.20 milestone. (Go1.19.2 now has #55951 backport issue.)

[gopherbot]

Change https://go.dev/cl/438501 mentions this issue: [release-branch.go1.18] regexp: limit size of parsed regexps

[gopherbot]

Change https://go.dev/cl/438499 mentions this issue: [release-branch.go1.19] regexp: limit size of parsed regexps