!#if-!#else-!#endif issue with unknown preprocessing tokens

[nicolas-yangli]

Prerequisites

• This is NOT a YouTube, Facebook, Twitch or a shortener/hosting site report. These sites MUST be reported by clicking their respective links.
• I read and understand the policy about what is a valid filter issue.
• I verified that this issue is not a duplicate. (Search here to find out.)
• I did not remove any of the default filter lists, or I have verified that the issue was not caused by removing any of the default lists.
• I did not enable additional filter lists, or I have verified that the issue still occurs without enabling additional filter lists.
• I do not have custom filters/rules, or I have verified that the issue still occurs without custom filters/rules.
• I am not using uBlock Origin along with other content blockers.
• I have verified that the web browser's built-in content blocker/tracking protection, network wide/DNS blocking, or my VPN is not causing the issue.
• I have verified that other extensions are not causing the issue.
• If this is about a breakage or detection, I have verified that it is caused by uBlock Origin and isn't a site issue.
• I did not answer truthfully to ALL the above checkboxes.

URL(s) where the issue occurs.

https://mikewang000000.github.io/ClashScan/

Description

The provided URL is a demo to fingerprint by scaning open ports on 127.0.0.1. When using a SOCKS5 proxy and also proxy DNS queries, the filter is not able to block access to 127.0.0.1.

I think this is related to this part in the filter list:

!#if cap_ipaddress
! https://github.com/uBlockOrigin/uBlock-issues/issues/1070#issuecomment-707237653
! https://github.com/uBlockOrigin/uBlock-discussions/discussions/910
*$3p,strict3p,ipaddress=lan,domain=~localhost|~127.0.0.1|~[::1]|~0.0.0.0|~[::]|~local
!#else

I tried copying /^\w+:\/\/127\.(?:(?:[1-9]?\d|1\d\d|2(?:[0-4]\d|5[0-5]))\.){2}(?:[1-9]?\d|1\d\d|2(?:[0-4]\d|5[0-5]))[:/]/$3p,domain=~localhost|~127.0.0.1|~[::1]|~0.0.0.0|~[::]|~local to custom filter list, without guarded by #if cap_ipaddress, it blocks access to 127.0.0.1.

Other extensions used

• Violentmonkey
• Stylus

Screenshot(s)

Screenshot(s)

Configuration

Details

uBlock Origin: 1.59.0
Firefox: 130
filterset (summary):
 network: 167781
 cosmetic: 72141
 scriptlet: 21520
 html: 1999
listset (total-discarded, last-updated):
 added:
  adguard-spyware-url: 1720-126, 1d.22h.9m
  block-lan: 62-0, 31m
  JPN-1: 15175-84, 3d.15h.53m
 default:
  user-filters: 9-0, never
  ublock-filters: 40547-138, 1h.17m Δ
  ublock-badware: 11173-6, 1h.17m Δ
  ublock-privacy: 1254-22, 1h.17m Δ
  ublock-unbreak: 2538-1, 1h.17m Δ
  ublock-quick-fixes: 139-8, 1h.17m Δ
  easylist: 85567-184, 1h.17m Δ
  easyprivacy: 53111-64, 1h.17m Δ
  urlhaus-1: 25255-0, 20h.59m
  plowe-0: 3546-993, 20h.58m
  CHN-0: 25223-102, 1d.22h.9m
filterset (user): [array of 9 redacted]
userSettings:
 advancedUserEnabled: true
hiddenSettings: [none]
supportStats:
 allReadyAfter: 287 ms (selfie)
 maxAssetCacheWait: 46 ms
 cacheBackend: indexedDB
popupPanel:
 blocked: 0

[stephenhawk8054]

I think it's more related to uBlock-issues repo. I'll transfer to that.

[gorhill]

The issue is not really related to using SOCKS5 proxies, it's a !#if-!#else-!#endif preprocessing issue.

When !#if is used with an unknown token, the intended behavior is to discard the preprocessing directives and to not ignore filters in the preprocessing block. However I see there is an issue now which is that the !#else block is not ignored and its content is discarded.

For example, the following should not cause all webpages to be blocked:

!#if cap_ipaddress
*$doc
!#else
@@*$doc
!#endif

But it does because @@*$doc is discarded, while it should not because cap_ipaddress is unknown token in 1.59.0. This needs to be fixed.

Meanwhile the conditional can be rewritten in the form:

!#if cap_ipaddress
*$doc
!#endif
!#if !cap_ipaddress
@@*$doc
!#endif

... to address the issue in the list until there is a fix in uBO itself.

[gorhill]

Test page: https://example.com/.

Unknown token, should not block -- was erroneously blocking before fix:

!#if huh
*$doc
!#else
@@*$doc
!#endif

Unknown token, should block -- was erroneously not blocking before fix:

!#if huh
!#else
*$doc
!#endif