85234842f9
Completes Phase 1. The gate now asks for FAN_CLOSE_WRITE alongside the permission events, so a threat written to disk is quarantined and a threat being executed is refused — one mechanism, one mark, no watch-descriptor ceiling and no blind spots outside a configured list. Verified live. The nicest evidence is an error message: $ chmod +x /tmp/hound-live/malware.sh chmod: cannot access '/tmp/hound-live/malware.sh': No such file or directory Hound had already quarantined it. `hound quarantine list` shows the entry, the clean binary beside it still runs, and CapPrm/CapEff/CapBnd read 000000000020000e. Three bugs, each of which looked like working code: * A file descriptor number is not an identity. The kernel allocates an fd per event and recycles the number the moment we close it, so one write arrives as FAN_OPEN_PERM on fd 6 and then FAN_CLOSE_WRITE on fd 6 again. Idempotency keyed on the fd treated the second as a duplicate of the first and dropped it — detection ran, matched EICAR, and threw the result away. Events now carry a monotonic seq that is never reused. * rename(2) fails EXDEV across filesystems, and for quarantine that is the common case rather than the exotic one: the vault is under /var/lib while threats land on /home, in a tmpfs, on a USB stick or in a container overlay. Quarantine now falls back to copy-then-unlink, unlinking only once the copy is safely down, and seals the stored file at 0600 with every execute bit cleared. * The capability set was too small to do the job. CAP_DAC_READ_SEARCH lets us read a threat but not unlink it, so quarantine failed EACCES as root. The set is now four capabilities — SYS_ADMIN, DAC_READ_SEARCH, DAC_OVERRIDE, FOWNER. DAC_OVERRIDE is close to "write anywhere" and that is worth being honest about; an antivirus that quarantines cannot avoid it, because the threat is by definition in a directory somebody else owns. What the reduction still buys is what it excludes, and there is a test asserting SYS_MODULE, SYS_BOOT, SYS_PTRACE, NET_ADMIN, NET_RAW, AUDIT_CONTROL and SETUID never creep back in. Narrowing further means a separate privileged helper for quarantine. realtime.rs is now documented as the unprivileged fallback and does not start when the gate is armed — running both would scan everything twice and quarantine the same file from two threads. 99 tests pass. HOUNDD_GATE_DEBUG=1 dumps every event and decision. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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