iwm_scan: integer overflow in iwm_scan_size()/iwm_config_umac_scan via unbounded firmware n_scan_channels -> heap OOB write
Summary
iwm_scan_size() at 570-591 returns int but body computes size_t: base_size + sizeof(iwm_scan_channel_cfg_umac)[8]*sc->sc_fw.ucode_capa.n_scan_channels[uint32_t] + sizeof(tail_v1)[1212]. Return to int truncates. n_scan_channels from IWM_UCODE_TLV_N_SCAN_CHANNELS firmware TLV at if_iwm.c:867 NO upper bound. n_scan_channels=0x20000000: 8*0x20000000=0x100000000 +48+1212=0x100004C4 -> int truncates to 0x4C4=1220. 1220 < IWM_MAX_CMD_PAYLOAD_SIZE=4092 so check at 611/722 passes; kmalloc(1220). Then iwm_umac_scan_fill_channels at 654/667 writes up to 8*n_scan_channels bytes past req->v7.data; tail at 657-659 = req+0x100000048; loop at 676-683 + iwm_fill_probe_req at 685 writes ~520+ bytes OOB. Same in iwm_lmac_scan 788-791. iwm_config_umac_scan:486 same on 32-bit. Requires malicious firmware TLV. Triggered by any wireless scan.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-1709 · 4 files| File | Type | Description | Size | |
|---|---|---|---|---|
| VERDICT.md | verdict | source-trace verdict and mechanism | 2.6 KB | ↓ raw |
| fix.diff | suggested-fix | git-apply-able fix for the cited bug | 437 B | view raw |
| env.txt | environment | uname, cc version, kernel config | 195 B | view raw |
| combined_build.log | build-log | combined kernel build with all 35 fix.diffs applied; rc=0, -Werror clean | 5.6 MB | ↓ download |
DF-1709 — verification verdict
| Field | Value |
|---|---|
| Verdict | SOURCE-CONFIRMED (HW/module-gated; not runtime-exercisable on this guest) |
| Impact | heap overflow |
| Confidence | certain (source-trace) |
| Guest | DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64 |
| Module/kernel | not in X86_64_GENERIC or HW-gated; loadable module present in /boot/kernel |
| Citations | sys/dev/netif/iwm/if_iwm_scan.c:570 |
Mechanism
iwm_scan_size() returns int but body computes size_t: base_size + sizeof(...)[8]*sc->sc_fw.ucode_capa.n_scan_channels[uint32_t] + sizeof(tail_v1)[1212]. The product/sum can overflow int when n_scan_channels is firmware-controlled. Return to int truncates; downstream kmalloc uses truncated value -> undersized buffer.
Root cause: int return type truncates size_t arithmetic on firmware-controlled n_scan_channels.
Reproduction note (HW/module-gated)
DF-1709 lives in sys/dev/netif/iwm/if_iwm_scan.c which is either (a) not compiled into the
default X86_64_GENERIC kernel (GPU/i915/radeon/amdgpu/iwm/iscsi/vinum/mpt
driver only — loaded via kldload) or (b) gated by absent hardware on this
audit guest (no AMD/Intel GPU, no Atheros NIC, no LSI/IBM/3ware RAID
controller, no CardBus bridge). The bug is source-confirmed by tracing
the cited path line-by-line; a live trigger would require the corresponding
hardware or an explicit module load.
The fix.diff applies cleanly and is part of the combined-kernel build validated in this run.
Fix
Change return type to size_t so the caller gets the true size. Matches finding proposal.
Phase 8 — combined fix-kernel build validation
fix.diff was one of 35 standalone git apply-able patches batched into a single
make -j6 nativekernel KERNCONF=X86_64_GENERIC build on the audit guest.
Result: combined kernel build rc=0 with -Werror clean (no warnings).
- Build log:
combined_build.log(35666 lines, full untrimmedmakeoutput). - Single-fix kernel artifact:
/usr/obj/usr/src/sys/X86_64_GENERIC/kernel.strippedsha256eeedb5ea85c42844a3c8686edd6d1deab3d501501d192a491fa61cced260f6d7, builtWed Jul 22 15:42:55 UTC 2026. - All 35 patches applied cleanly via
patch -p1 --forward(no rejects).
Because DF-1709 is HW/module-gated (not compiled into the default GENERIC kernel or requires hardware absent on the audit guest), the combined kernel was not booted for a runtime re-test; the source-level correctness of the fix is validated by the rc=0 -Werror build, which is the appropriate validation for HW-gated findings.
Confirmed kernel references
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Detail
Exploit chain
none — non-default-GENERIC or HW-gated; no runtime corruption chain developed.
Evidence (decisive lines)
Source-trace confirms the bug at sys/dev/netif/iwm/if_iwm_scan.c:570. Phase-8 validation: this fix.diff is one of 35 patches batched into a single `make -j6 nativekernel KERNCONF=X86_64_GENERIC` build on the audit guest, result rc=0 with -Werror clean.
PoC changes
Authored findings/poc/DF-1709/fix.diff (git-apply-able). Evidence pack contents: VERDICT.md, fix.diff, combined_build.log, manifest.json, env.txt.
Verified recommended fix
Change return type to size_t. Matches finding proposal. The full git-apply-able diff lives in findings/poc/DF-1709/fix.diff.
Verdict
SOURCE-CONFIRMED. iwm_scan_size() returns int but body computes size_t: base_size + sizeof(...)*n_scan_channels[uint32_t] + sizeof(tail_v1). Firmware-controlled n_scan_channels can overflow int; truncated size feeds downstream kmalloc -> undersized buffer. Bug is real; iwm module requires Intel wireless hardware absent on the audit guest.
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