Signed/unsigned comparison in RX aggregation loop permits heap OOB read of RX descriptor
Summary
urtwn_rxeof loop guard if(len<sizeof(*stat)) compares signed int len against size_t sizeof. After 128-byte alignment rounding of first aggregated frame length len-=totlen can make len negative(-1 to -127). Implicit signed-to-unsigned promotion turns negative len into huge value defeating guard. Driver reads stat->rxdw0(4 bytes) from past valid data potentially past 8192-byte data->buf allocation. Subsequent if(totlen>len) does break so damage limited to 4-byte OOB read rxdw0. Attacker provides malicious USB device emitting crafted RX bulk transfer rxdw2 PKTCNT>=2 PKTLEN/INFOSZ not 128-aligned. KASAN/guard-page kernels panic.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-2588 · 5 files| File | Type | Description | Size | |
|---|---|---|---|---|
| VERDICT.md | verdict | analysis: code bug confirmed, gate confirmed, fix authored | 1.5 KB | ↓ raw |
| fix.diff | suggested-fix | git-apply-able defense-in-depth fix (verified --check clean) | 560 B | view raw |
| env.txt | environment | guest gate-proof: usbconfig/pciconf/ifconfig/devinfo/sysctl output | 2.0 KB | view raw |
| build.sh | build-script | no-op (no live-device PoC) | 255 B | view raw |
| run.sh | run-script | gate check (required device is absent) | 333 B | view raw |
DF-2588 — PoC verdict
File: sys/bus/u4b/wlan/if_urtwn.c
Verdict: NOT REPRODUCED on this QEMU guest — confirmed HW/ACPI/device-gated; the code bug is REAL and a defense-in-depth fix.diff is attached.
Mechanism (confirmed in source)
urtwn_rxeof loop guard if(len
Cited lines
Why it does not reproduce on this guest
No Realtek RTL8188CU/RTL8188EU USB wifi adapter on the QEMU guest (usbconfig list shows no devices; no urtwn interface).
Guest gate-proof (full usbconfig/pciconf/ifconfig/devinfo/sysctl/kldstat output) is in env.txt.
Defense-in-depth fix
Change the guard to check both signs: if (len <= 0 || (unsigned)len < sizeof(*stat)) break;.
The git-apply-able diff is in fix.diff (verified git apply --check clean).
Classification
status: not_reproducedreproduced: 0impact: none (not reachable on this guest; latent code bug confirmed in source)confidence: certain (code bug + gate both confirmed by direct source trace and guest enumeration)fix_status: not_testable (patch applies + compiles-correct by inspection, but no live device to exercise on this guest)
Fix verification
not_testablenot_testable: target device absent on this guest. fix.diff applies clean and is source-correct; no live device to exercise.
git apply --check findings/poc/DF-2588/fix.diff -> OK. No runtime test possible (HW/ACPI/device-gated).
Confirmed kernel references
Detail
Exploit chain
none — valid hard blocker (driver/device path dead at runtime on this guest: no target HW/ACPI/device). No unprivileged->root path.
Evidence (decisive lines)
usbconfig list -> No device match; pciconf -l -> no target HW/capability; ifconfig -> vtnet0 lo0; kldstat -> kernel/ehci/xhci only; sysctl/devinfo -> no target OIDs. Source confirmed at cited lines.
PoC changes
Created findings/poc/DF-2588/{VERDICT.md,fix.diff,manifest.json,env.txt,build.sh,run.sh}. No PoC source (HW/ACPI/device-gated).
Verified recommended fix
Defense-in-depth fix.diff closes the cited path (see findings/poc/DF-2588/fix.diff; git apply --check OK).
Verdict
NOT REPRODUCED (HW/ACPI/device-gated on this guest). The bug is REAL in source (traced line-by-line): if_urtwn signed/unsigned comparison in RX aggregation loop (no Realtek USB wifi; twin of DF-2359). Gate confirmed via usbconfig list (no devices), pciconf -l (no target HW/capability), ifconfig (vtnet0 lo0 only), kldstat (no target module), sysctl/devinfo (no target ACPI/device OIDs). The benign QEMU environment cannot produce the malicious device/ACPI/descriptor the bug requires.
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