cardbus_cis: unbounded CIS tuple-chain offset allows OOB read past BAR mapping (panic / MAC info leak)
Summary
cardbus_parse_cis do/while loop (670-692) walks CIS chain keyed solely on CISTPL_END. off incremented len+2 per iter (436,455) NO comparison to BAR resource size NO iteration cap. cardbus_read_tuple_mem (441-457) derefs bus_space_read_1(bt,bh,start+*off) + bus_space_read_region_1(bt,bh,*off+start+2,tupledata,*len). x86_64 bus_space_read_1 = *(volatile u8*)(handle+offset) NO bounds check. BAR mapping min 4096 bytes (535-536). 16 tuples len=255 -> off=4112 >4096 -> OOB read past mapping -> panic if unmapped adjacent VA; or OOB bytes into tupledata -> if parse as FUNCE LAN_NID -> 6 bytes kernel heap exposed as MAC via PCI_IVAR_ETHADDR readable by ifconfig. ROM scan same defect: imagebase+=imagesize<<9 (615) up to ~32MB/step. Malicious CardBus card or QEMU emulated PCI device. Fix: bound off against rman_get_size(res); iteration cap.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-1810 · 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 | 709 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-1810 — verification verdict
| Field | Value |
|---|---|
| Verdict | SOURCE-CONFIRMED (HW/module-gated; not runtime-exercisable on this guest) |
| Impact | DoS / OOB read |
| 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/pccard/cardbus/cardbus_cis.c:670 |
Mechanism
cardbus_parse_cis do/while loop (670-692) walks the CIS chain keyed solely on CISTPL_END. off is incremented len+2 per iteration with NO comparison to the BAR resource size and NO iteration cap. A malicious CardBus card omitting CISTPL_END causes the loop to walk forever reading past BAR resources.
Root cause: Unbounded CIS-chain walk keyed only on a card-controlled terminator.
Reproduction note (HW/module-gated)
DF-1810 lives in sys/dev/pccard/cardbus/cardbus_cis.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
Cap the loop at cis_max=4096 iterations and abort cleanly when exceeded. 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-1810 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/pccard/cardbus/cardbus_cis.c:670. 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-1810/fix.diff (git-apply-able). Evidence pack contents: VERDICT.md, fix.diff, combined_build.log, manifest.json, env.txt.
Verified recommended fix
Cap the loop at cis_max=4096 iterations and abort cleanly when exceeded. Matches finding proposal. The full git-apply-able diff lives in findings/poc/DF-1810/fix.diff.
Verdict
SOURCE-CONFIRMED. cardbus_parse_cis do/while loop (670-692) walks the CIS chain keyed solely on CISTPL_END. off is incremented len+2 per iteration with NO comparison to the BAR resource size and NO iteration cap. A malicious CardBus card omitting CISTPL_END causes the loop to walk forever reading past BAR resources. Bug is real; cardbus is compiled into GENERIC but requires CardBus bridge hardware absent on the audit guest.
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