sandboxing: known issues in seccomp filters

[hg8]

Known issues identified by security auditors for the Sandboxing / Seccomp subsystem.
Listed for the Immunefi bug bounty contest to prevent duplicate reports.

Note: Detailed reproduction steps and exploit specifics are intentionally omitted.

1. 32-bit argument check bypass on x86_64

• Impact: Sandbox Escape
• Code: contrib/codegen/generate_filters.py
• Summary: Seccomp BPF filter code generator only checks the lower 32 bits of syscall arguments on x86_64, allowing filter bypass.
• Ref: auditor-internal#464

[hg8]

2. Supplementary groups survive sandbox entry

• Impact: Sandbox hardening
• Code: src/util/sandbox/fd_sandbox.c#L628-L635
• Summary: Supplementary groups are not cleared during sandbox entry, retaining unintended host filesystem authority in tiles that preserve a host dirfd post-sandbox.
• Ref: auditor-internal#505