DF-4992

Failed SMB_READB/SMB_READW/SMB_PCALL transfers reported as success: copyout result clobbers the bus error

Summary

The copyout result overwrites the smbus error in the rbuf branch - failed transactions return ioctl()==0 with rdata untouched (fabricated data). Short-circuit-on-error fix.

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Severity: Info
Status: new
Bucket: Base system — drivers
Confidence: certain
Pass: 2 · GLM 5.3 second pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N
CWE: CWE-252
File: sys/dev/smbus/smb/smb.c
Lines: 272-303
Area: dev
Discovered: 2026-09-25
Updated: 2026-09-25

Team triage

untriaged

priority: — · owner: —

PoC verification

untested

Status: untested
Reproduced: no
Impact: none
Confidence: certain
Tested: 2026-09-25 17:15:59
Attempts: 0
Runtime: —
Code hash: —
Guest: —
Build cmd: —
Run cmd: —

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Fix verification

not_testable

Fix status: not_testable
Baseline reproduced: —
Patched reproduced: —
Confidence: certain
Tested: 2026-09-25 17:15:59
Runtime: —
Kernel: per-fix-DF-4992
fix.diff: findings/poc/DF-4992/fix.diff
Runner: df-bsd-reviewer

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PoC verification

Evidence pack

findings/poc/DF-4992 · 1 files

File	Type	Description	Size
verdict.json	file		759 B	view raw

Fix verification

not_testable

per-fix-DF-4992

Confirmed kernel references

sys/dev/smbus/smb/smb.c:272-303

Detail

Exploit chain

failed SMB read -> ioctl success + stale rdata

Evidence (decisive lines)

findings/poc/DF-4992/ (this verdict)

Verdict

Logic defect, root-gated (Info): all three read ioctls assign error=smbus_error(...) then immediately overwrite it with error=copyout(...) inside the rbuf branch - a failed/no-ACK transaction returns ioctl()==0 and the caller's struct carries rdata untouched (fabricated 'data' from the caller's own input). Monitoring tools cannot distinguish failed reads. Short-circuit-on-error fix.