Re: [PATCH v3] perf cap: Remove used_root parameter and simplify capability checks

[Namhyung Kim]

On Wed, Jul 22, 2026 at 10:06:40PM -0700, Ian Rogers wrote:
> Refactor perf_cap__capable() to completely remove the used_root out-parameter
> as requested by the maintainer. Relying on an explicit used_root boolean
> poisoned sequential capability checks (e.g. failing CAP_SYS_ADMIN checks
> poisoning the flag for subsequent CAP_PERFMON evaluations for unprivileged
> users) and created redundant complexity across check_ftrace_capable(),
> symbol__read_kptr_restrict(), and perf_event_paranoid_check().
> 
> Streamline the capability API to perform a pure true/false boolean
> evaluation. The function checks the Effective set using SYS_capget; if
> the syscall is missing or fails on legacy kernels, it cleanly falls back
> to checking EUID == 0. This perfectly preserves modern capability-aware host
> sessions, guarantees transparent fallback for older kernels, and correctly
> rejects privileged operations for containerized root processes that have
> explicitly dropped their capability bounding and permitted sets.

Applied to perf-tools-next, thanks!

Best regards,
Namhyung