[mgradwohl]

Description

Part of #2728: slices 1 and 2 of three for "processes hidden by hidepid (the helper lists them)". The maintainer chose this design: for each hidden PID, the helper returns the raw text of a fixed allow-list of /proc/<pid> files, and TaskSmack parses it with its own probe's parsers. Running the probe in the root helper was rejected.

Slice 1: the parsing seam (no behavior change for enumerate())

• LinuxProcessProbe's stat, statm, status, io and cgroup readers each split into the read through the /proc/<pid> handle (unchanged, caches and status re-read included) and an apply…(text) half.
• New public processFromFiles(pid, ProcFileTexts) builds a record from text alone: the same parsers, applyCmdline(), and readProcessCommand()'s zombie rule. The FD count and network counters stay unknown for the helper's counters read (feat(linux): tasksmack-helper reads other users' FD counts and I/O bytes for the Processes table (#2728) #2938, feat(linux): tasksmack-helper's socket inodes attribute other users' connections in the Processes table (#2728) #2947) to fill. The architecture is left unknown.

Slice 2: protocol v6 and the helper reader

• ListHiddenProcesses (40): carries the PIDs TaskSmack already sees (capped at MAX_VISIBLE_PIDS, 2^18).
• HiddenProcessesResult (57): for every other process, its target (PID plus the start time its stat names) and the text of stat, statm, status, cmdline, io and cgroup only, each capped at MAX_STRING_BYTES. cmdline has a read flag, so an unreadable one isn't mistaken for a kernel thread; a command line the flag says wasn't read is refused. The reply stops short of a frame or of MAX_HIDDEN_PROCESSES (2^14) and says it was cut.
• Helper: HiddenProcessesRead.h opens each process's directory once and reads through that handle, so all the text comes from the process its stat names. A process that exits mid-read is left out. Windows' helper answers with an error, since Windows has no hidepid.
• Other updates: fuzz seeds moved to v6 plus two new ones; dict (including the stale header_version_* entries); helper-handshake.py's v6 Hello; and tasksmack.md's list of what the helper answers.

Next (slice 3): BrokeredProcessProbe sends ListHiddenProcesses when capabilities() says processes are hidden and a helper session is running, builds records with processFromFiles(), and merges them in. Their FD counts and network counters then come from the existing counters read.

PR Size

🔴 Large (~700 lines across ~45 files). About half is tests, and 26 of the files are one-byte fuzz seed bumps.

Type of Change

• New feature (non-breaking change that adds functionality)

Checklist

• I have read the CONTRIBUTING guidelines
• My code follows the project's coding standards
• I have run clang-tidy and addressed any warnings
• I have run clang-format on my changes
• I have run pre-commit run --all-files or installed pre-commit hooks
• I have added tests that prove my fix/feature works
• All new and existing tests pass
• I have updated documentation as needed

Testing

TASKSMACK_REQUIRE_DISPLAY=1 TASKSMACK_REQUIRE_SDBUS=1 xvfb-run -a env -u WAYLAND_DISPLAY ctest --preset debug -j 4   # 683/683

New tests:

• Probe: LinuxProcessProbeTest.ARecordFromTheFilesTextIsTheOneEnumerateBuilds, and …TreatsAZombieOrAnUnreadCommandLineAsEnumerateDoes.
• Protocol: BrokerProtocolTest.HiddenProcessesRoundTripAndRefuseTooManyOrAStrayCommandLine and …HiddenProcessesPastAFrameAreCutAndSaySo.
• Mapping: BrokerRequestMappingTest.AHiddenProcessesRequestGoesToItsReaderWithTheVisiblePids, including the error from a throwing reader and from a helper without one.
• Reader: HiddenProcessesReadTest.*, over a fixture /proc: visible PIDs skipped, an exited process left out, an unread cmdline, a missing root.
• Real helper: PkexecBrokerTest.TheHelperListsTheProcessesTaskSmackDoesntSee, under its enforcing seccomp filter ([Security] tasksmack-helper: add a seccomp allow-list (and maybe Landlock) after the capability drop; UID 0 + CAP_SYS_PTRACE isn't containment #2752).
• Windows: BrokerPipeServeTest counts the new request as a read.

Additional Notes

v0.10.0, no backport. Stays a draft while my lane already has two PRs out of draft.

🤖 Generated with Claude Code

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None