{
  "finding_id": "DF-5248",
  "status": "inconclusive",
  "reproduced": false,
  "impact": "none",
  "confidence": "certain",
  "verdict": "run_drain_fifo() (if_run.c:2513-2559) has an unbounded for(;;) whose only exit is !(stat & RT2860_TXQ_VLD), but the run_read() return value is ignored (2515) and run_read() returns 0xffffffff on USB failure (if_run.c:1254), which has VLD (bit 0) set. A device that stops answering control transfers or a hostile always-VLD device makes the loop eternal; each iteration costs up to 10x250ms in run_do_request retries (1223-1242), wedging the net80211 cmdq task and hanging run_detach()s ieee80211_draintask (879-880) forever - device_detach never returns. Both non-termination conditions demonstrated by drain_fifo_loop.c with the exact kernel expressions (1e6-iteration cap never reached an exit). In-kernel repro hardware-gated -> inconclusive; control-flow logic is certain.",
  "exploit_chain": "hostile/unplugged run(4) device during hostap TX-stat drain -> infinite bounded-cost loop in task thread -> net80211 task wedge + permanent device_detach hang (persistent kernel DoS until reboot)",
  "evidence": "findings/poc/DF-5248/run.log: both scenarios NEVER TERMINATES after 1000000 iterations; if_runreg.h:664 RT2860_TXQ_VLD=(1<<0); if_run.c:1254 error value 0xffffffff",
  "kernel_refs": [
    "sys/bus/u4b/wlan/if_run.c:2513",
    "sys/bus/u4b/wlan/if_run.c:2515",
    "sys/bus/u4b/wlan/if_run.c:1254",
    "sys/bus/u4b/wlan/if_run.c:879",
    "sys/bus/u4b/wlan/if_runreg.h:664"
  ],
  "poc_changes": "Harness written from scratch (no seed)",
  "attempts": 1,
  "guest_uname": "DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026  root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64",
  "runtime_sec": 3,
  "guest_dirty": 0,
  "build_cmd": "cc -O2 -o /tmp/drain_fifo_loop /tmp/drain_fifo_loop.c",
  "run_cmd": "/tmp/drain_fifo_loop",
  "code_hash": "817307945798bf77a118a0c50e8f8b2f47149e6066dc1f4a7c7aa76cfd653a27",
  "notes": "Same hostile-USB-device trust boundary as the known DF-0981/DF-2358 RX findings; also reachable by plain unplug at the wrong moment because the error path itself cannot exit the loop.",
  "recommended_fix": "Bound the FIFO drain loop (hardware FIFO is 16 deep) and break on run_read() error",
  "fix_status": "not_testable",
  "fix_baseline_reproduced": 0,
  "fix_patched_reproduced": 0,
  "fix_verdict": "fix.diff authored and verified with git apply --check against the pristine sys/ tree, but cannot be kernel-tested: the QEMU guest has no USB controller and no run(4) device model exists, so neither baseline nor patched kernel behavior is exercisable. Hardware-gated: not_testable.",
  "fix_evidence": "fix.diff (git-apply clean); VERDICT.md"
}