Greptile Summary

This PR fixes a security vulnerability where malicious clients could bypass the pvpwithnoteam pvp mode by sending team changes through spawn packets, and prevents fast team-switching exploits.

Key Changes:

• HandlePlayerSpawn now validates team assignments and enforces pvpwithnoteam mode before processing spawns
• Added InitialTeamChangePending mechanism to allow legitimate initial team selection for non-SSC players while preventing abuse
• Split up HandlePlayerTeam and HandleTogglePvp checks to properly handle pvp mode restrictions separately from fast-switch prevention
• OnSecondUpdate continuously enforces pvp mode settings (hostile flag and team) every second as a safety net
• Non-SSC spawn handling now duplicates vanilla logic to maintain control over team assignments and broadcasts

Issues to Address:

• Edge case bug exists where teamCorrectNeeded resets team to player's current non-zero team instead of enforcing team 0 for pvpwithnoteam mode (lines 2978-2979 and 3007-3008). This occurs when the fast-switch check triggers while pvp mode is pvpwithnoteam and player has a non-zero team. Suggested fix already provided in previous comments.

Confidence Score: 3/5

• Safe to merge after fixing edge case bugs in team correction logic
• Core security fix is sound, but edge case bugs at lines 2978-2979 and 3007-3008 could allow pvpwithnoteam bypass when fast-switch check triggers while player has non-zero team. Fix is straightforward and already suggested in previous comments.
• TShockAPI/GetDataHandlers.cs requires fixes at lines 2978-2979 and 3007-3008 before merge

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[PlayerSpawn packet received] --> B{pvpMode == pvpwithnoteam<br/>AND team != 0?}
    B -->|Yes| C[Force team = 0<br/>Set teamCorrectNeeded]
    B -->|No| D{Team change attempt<br/>AND < 5 sec since last?}
    C --> D
    D -->|Yes| E[Set teamCorrectNeeded]
    D -->|No| F{First spawn?}
    E --> F
    F -->|Yes| G{Non-SSC AND<br/>team != 0 AND<br/>!teamCorrectNeeded?}
    F -->|No| H{SSC enabled?}
    G -->|Yes| I[Set InitialTeamChangePending<br/>LastPvPTeamChange = Now]
    G -->|No| H
    I --> H
    H -->|Yes| J[SSC spawn path]
    H -->|No| K[Non-SSC spawn path]
    J --> L{team != TPlayer.team?}
    K --> M{teamCorrectNeeded?}
    L -->|Yes| N{teamCorrectNeeded?}
    L -->|No| R[Spawn player]
    N -->|Yes| O[BUG: team = TPlayer.team<br/>should enforce 0 for pvpwithnoteam]
    N -->|No| P[Update LastPvPTeamChange]
    O --> Q[TPlayer.team = team<br/>Broadcast spawn]
    P --> Q
    Q --> R
    M -->|Yes| O
    M -->|No| S{!InitialTeamChangePending<br/>AND team changed?}
    S -->|Yes| T[Update LastPvPTeamChange]
    S -->|No| U[TPlayer.team = team<br/>Broadcast spawn]
    T --> U
    R --> V{teamCorrectNeeded?}
    U --> V
    V -->|Yes| W[Send corrected team<br/>back to client]
    V -->|No| X[Done]
    W --> X
    
    style O fill:#ffcccc
    style C fill:#ccffcc
    style E fill:#ffffcc

_{Last reviewed commit: 1736112}

@greptile review?

The edge case should be resolved by 55a819d, where I set the player's team to 0. Since it's already 0, there should be no edge case. Tested with a 3rd-party client using code execution to run code that sets my team and then spawns my player, I could not replicate anything.
To also fix another bug regarding PVP mode being switched while the server is running, and to prevent any more possible issues, TShock.OnSecondUpdate now checks it and appropriately sets the pvp status and team of the player.

@greptile review

I don't really see the edge case here. Since the player's team is always set to 0 when using pvpwithnoteam as the pvp mode now, it shouldn't ever be able to not be 0 when team correction is needed. Especially since now, every second, the player's team is checked and corrected to 0 if it's not.

Please do not use conventional commits.

My apologies. if you can clarify what you mean by that, I will avoid it in the future.

Better off closing and redoing this PR to squash everything into one commit?