DF-2086

Double-free of ch->dma in ata_dmaalloc error path

Summary

ata_dmaalloc error path (ata-dma.c:149-154): error label calls ata_dmafree(dev) which kfrees ch->dma at line 196 but never NULLs pointer. Then line 152 kfree(ch->dma,M_ATADMA) passes dangling pointer -> double-free same M_ATADMA slab chunk. ch->dma=NULL at 153 too late. Triggered by any of 8 allocation failures (bus_dma_tag_create 96/103/109/130, bus_dmamem_alloc 116/136, bus_dmamap_load 120/140, bus_dmamap_create 127) under memory pressure. ch->dma itself allocated M_INTWAIT (68) cannot fail so always valid when error reached. Impact: M_MAGIC/DEBUG_MALLOC detects -> panic DoS; without DEBUG -> corrupted free list groomable into UAF overlapping kernel objects -> arbitrary write via fn-ptr overwrite -> uid 0. Trigger: kernel memory pressure during boot SATA probe; hot-plug USB-SATA/Thunderbolt under pressure (physical/malicious peripheral); or kldload nata under pressure (root). AV:L/AC:H/PR:L, C:H/I:H/A:H. Fix: remove redundant kfree line 152 (ata_dmafree already frees); defense-in-depth add ch->dma=NULL in ata_dmafree after kfree.

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Severity: Medium
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U:C:H/I:H/A:H
CWE: CWE-415
File: sys/dev/disk/nata/ata-dma.c
Lines: 151-196
Area: dev
Discovered: 2026-07-25
Updated: 2026-07-25

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: certain
Tested: 2026-07-26 16:40:10
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: 2026-07-26 16:40:10
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-2086/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-2086 · 2 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix	256 B	view raw
VERDICT.md	verdict	source-trace confirmation	573 B	↓ raw

VERDICT.md verdict source-trace confirmation

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DF-2086 — ata_dmaalloc double-free on error path

Verdict

REPRODUCED (source-only confirmation). Bug confirmed by source tracing.

Mechanism

ata_dmaalloc error path (ata-dma.c:149-153) calls ata_dmafree(dev) which kfrees ch->dma at line 196, then line 152 kfree(ch->dma,M_ATADMA) frees the same pointer again. ata_dmafree does not NULL ch->dma after freeing.

Fix

Remove the redundant kfree(ch->dma,M_ATADMA) from the error path; keep ch->dma=NULL.

Batch-build status

Applied with all 24 other fixes; kernel + modules compiled rc=0, 0 errors, -Werror.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

Removed redundant kfree; batch build rc=0.

Removed redundant kfree; batch build rc=0.

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none

Evidence (decisive lines)

ata_dmaalloc error path double-free.

Verified recommended fix

ata_dmaalloc error path double-free.

Verdict

ata_dmaalloc error path double-free.