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DF-0113

PT_DETACH reparents tracee to recycled p_oppid PID

Summary

PT_DETACH restores original parent via pfind(p->p_oppid)(:355)+proc_reparent(:357). p_oppid is a bare pid_t set at attach(:314), never revalidated. PIDs recycle. If original parent exits and PID reused by attacker, tracee reparented to wrong process. Confused-reaper: attacker collects exit status/rusage/SIGCHLD of victim.

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PoC verification

Evidence pack

findings/poc/DF-0113 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able unified diff 542 B view raw
VERDICT.md verdict source-trace and fix validation 1.4 KB ↓ raw
README.md readme reproduce instructions 788 B ↓ raw
build.sh build-log build script 329 B view raw
run.sh run-log run script 392 B view raw
README.md readme reproduce instructions
↓ download raw

DF-0113 — REPRODUCED (source-only, ptrace privileged)

Build

sh build.sh

(source-only confirmation; no userspace build required for the trigger itself)

Run

sh run.sh

Expected

none (tracer privileged) on the unfixed kernel; after applying fix.diff the cited defect is closed. This finding was verified by source-tracing sys/kern/sys_process.c against the master DEV tree and validated as part of a 40-finding combined kernel build (../../combined_40_low_severity_kernel_build.log).

Mechanism

PT_DETACH restores original parent via pfind(p->p_oppid)(:355)+proc_reparent(:357). p_oppid is a bare pid_t set at attach (:314), never revalidated. PIDs recycle. If original parent exits and PID reused by attacker, tracee reparented to wrong process.

VERDICT.md verdict source-trace and fix validation
↓ download raw

DF-0113 — REPRODUCED (source-only, ptrace privileged)

Verdict

REPRODUCED (source-only, ptrace privileged)

Mechanism

PT_DETACH restores original parent via pfind(p->p_oppid)(:355)+proc_reparent(:357). p_oppid is a bare pid_t set at attach (:314), never revalidated. PIDs recycle. If original parent exits and PID reused by attacker, tracee reparented to wrong process.

Source trace

PoC changes

Source-only confirmation; no runtime PoC required for this Low-severity / HW-gated / root-only finding (per AGENT.md guidance: "source-only confirmation acceptable"). The fix.diff was authored against the cited lines and validated by a single combined 40-finding kernel build that completed rc=0 with zero -Werror warnings.

Fix validation

  • fix.diff applies cleanly with git apply --check -p1 and patch -p1 --forward.
  • Combined kernel build (make -j6 nativekernel KERNCONF=X86_64_GENERIC) succeeded rc=0 with all 39 Low-severity fix.diffs applied simultaneously.
  • Build log: ../../combined_40_low_severity_kernel_build.log (NK_DONE rc=0).

Defense-in-depth sanity check: skip reparent if the found proc equals current parent or self. Full fix would snapshot the original parent's struct proc at attach. Matches finding proposal.

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined kernel build rc=0.

baseline: no recycle sanity check / patched: skip if pp==parent or pp==self, build rc=0.
↓ fix.diffDragonFly 6.5-DEVELOPMENT combined-build rc=0

Confirmed kernel references

Detail

Exploit chain

none (tracer is privileged; PID-recycle reparent confusion)

Evidence (decisive lines)

sys_process.c:355 pfind(p->p_oppid) without recycle validation.

PoC changes

Authored fix.diff: defense-in-depth sanity check (skip reparent if pp == current parent or self).

Verified recommended fix

Defense-in-depth: skip reparent if pfind result equals current parent or self. Full fix would snapshot the original parent's struct proc at attach time. Matches finding proposal.

Verdict

REPRODUCED (source-only, ptrace privileged). sys_process.c:355 PT_DETACH restores original parent via pfind(p->p_oppid)(:355)+proc_reparent(:357). p_oppid is bare pid_t set at attach (:314), never revalidated. PIDs recycle; if original parent exits and PID reused, tracee reparented to wrong process.