DF-1115

Dead switch-error check in mmc_switch_status compares a status field to a raw bit value

Summary

mmc_switch_status at mmc_subr.c:211 does R1_CURRENT_STATE(status) == R1_SWITCH_ERROR. R1_CURRENT_STATE(x) extracts 4-bit field (values 0-15) via mmcreg.h:145; R1_SWITCH_ERROR is a raw status bit (1u<<7=128). A 4-bit field (max 15) can NEVER equal 128, so predicate is provably always false. Switch errors from malicious/emulated MMC card silently ignored, mmc_switch returns MMC_ERR_NONE. Only consumer of R1_SWITCH_ERROR in entire sys/ tree. Intended check is bit test: (status & R1_SWITCH_ERROR) != 0. Impact: host proceeds with bus-width/speed/partition config the card rejected -> data corruption / DoS. Requires malicious/emulated MMC card; no userspace-only trigger.

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Severity: Low
Status: new
Bucket: Base system — bus / platform / cpu
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U:C:N/I:L/A:L
CWE: CWE-570 Expression is Always False
File: sys/bus/mmc/mmc_subr.c
Lines: 211-212
Area: hw
Discovered: 2026-07-15
Updated: 2026-07-15

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: certain
Tested: 2026-07-25 10:25:03
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-25 10:25:03
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1115/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1115 · 3 files

File	Type	Description	Size
VERDICT.md	verdict	Source-confirmation verdict for DF-1115	627 B	↓ raw
fix.diff	suggested-fix	Fix dead == comparison to bitwise AND for R1_SWITCH_ERROR	346 B	view raw
../fix_build.log	build-log	Batch kernel build log (all fixes, rc=0)	5.6 MB	↓ download

VERDICT.md verdict Source-confirmation verdict for DF-1115

↓ download raw

DF-1115 Verification Verdict

Severity: Low Impact class: logic Verification method: Source-only confirmation (HW-gated, not triggerable on QEMU guest)

Verdict: REPRODUCED (source-confirmed)

The bug is confirmed in the audited source at the cited path:line. Triggerable but requires specific driver/config.

Fix: Fix dead == comparison to bitwise AND for R1_SWITCH_ERROR

Fix applied and validated in batch kernel build (rc=0, -Werror).

Fix validation

All 41-fix patches batched into single make -j6 nativekernel KERNCONF=X86_64_GENERIC build. Build result: rc=0, 0 errors (full -Werror clean).

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none

Evidence (decisive lines)

REPRODUCED (source-only): mmc_switch_status compares R1_CURRENT_STATE(status) (4-bit field, 0-15) == R1_SWITCH_ERROR (raw bit 1<<7=128); comparison is always false, switch-error detection is dead.

Verified recommended fix

REPRODUCED (source-only): mmc_switch_status compares R1_CURRENT_STATE(status) (4-bit field, 0-15) == R1_SWITCH_ERROR (raw bit 1<<7=128); comparison is always false, switch-error detection is dead.

Verdict

REPRODUCED (source-only): mmc_switch_status compares R1_CURRENT_STATE(status) (4-bit field, 0-15) == R1_SWITCH_ERROR (raw bit 1<<7=128); comparison is always false, switch-error detection is dead.