Stack buffer overflow/underflow in ad_describe via unterminated model string
Summary
ad_describe() calls index() (strchr) on atadev->param.model a 40-byte ATA IDENTIFY field NOT guaranteed NUL-terminated. btrim/bpack in ata-all.c only conditionally NUL-terminate. A 40-byte space/dash/NUL-free model survives without terminator. index() scans past model[39] into adjacent IDENTIFY words; if finds 0x20 or 0x2d there before NUL computed len exceeds 40. Then strncpy(product model+len 40-len) evaluates 40-len with len>40 as negative int widened to size_t near SIZE_MAX strncpy attempts ~2^64 bytes into 64-byte product[] stack buffer smashing saved registers/return address. vendor[40-len]=0 writes NUL at negative index before vendor[]. Attacker: malicious ATA/SATA device USB-to-SATA bridge flashable controller FPGA hypervisor. Path runs automatically at boot/hotplug NO privilege NO interaction.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-2488 · 7 files| File | Type | Description | Size | |
|---|---|---|---|---|
| VERDICT.md | verdict | HW-gate analysis + source trace + fix summary | 1.9 KB | ↓ raw |
| fix.diff | suggested-fix | git-apply-able defense-in-depth fix (applies + compiles) | 1.3 KB | view raw |
| fix_build.log | build-log | combined build proof: all 18 fix.diffs compile in X86_64_GENERIC (-Werror, rc=0); each diff also passes git apply --check | 404 B | view raw |
| manifest.json | manifest | this catalog | 1.5 KB | view raw |
| env.txt | environment | guest uname + PCI/kldstat/dev inventory proving the gate | 3.6 KB | view raw |
| build.sh | build-script | no-op (HW-gated, nothing to build) | 356 B | view raw |
| run.sh | run-script | no-op (HW-gated, nothing to run) | 268 B | view raw |
DF-2488 — Stack buffer overflow/underflow in ad_describe via unterminated ATA model
Verdict
NOT REPRODUCED (hardware / trigger gated). The cited vulnerable code path exists
in sys/dev/disk/nata/ata-disk.c and is compiled into the X86_64_GENERIC kernel, but it is not
exercisable at runtime on this QEMU guest because the required HBA / device /
trigger is absent. Confidence in the source bug itself: certain.
Why it cannot be reproduced here (the gate)
Hard-gated: needs an nata ATA DISK (ad%d). The guest has only the QEMU DVD-ROM (acd0); no /dev/ad* exists, so ad_describe() is never invoked at runtime.
See env.txt for the full guest PCI/kldstat/dev-node inventory that proves the
gate.
The bug is real in source (traced line-by-line)
Cited path:
- sys/dev/disk/nata/ata-disk.c:508-519
- The vulnerable construct is present verbatim in the current master source
(confirmed by direct read of the cited lines during verification).
- A defense-in-depth fix.diff that closes the path is included and was
validated to apply (git apply --check) and to compile cleanly in a full
X86_64_GENERIC kernel build with -Werror (build rc=0).
Fix
Replace the unbounded index()/strchr() on the 40-byte model field with a width-bounded search and clamp len to [0,40], so strncpy()/vendor[] never receive a negative (sign-extended ~SIZE_MAX) length.
The standalone git-apply-able diff is fix.diff.
Reproduce
./build.sh && ./run.sh — both are no-ops on this guest by design (the gate
holds). Exercising the path requires the corresponding HBA/device/trigger
(ATA disk / ATAPI floppy or tape / NVMe controller / AdvanSys HBA / AHCI
controller / a malicious ATAPI device / a CD burner / hot-unplug).
Status
status: not_reproduced | reproduced: 0 | impact: none (HW-gated) fix_status: not_testable (path cannot run on this guest; diff applies + compiles)
Fix verification
not_testablenot_testable: the vulnerable path is unreachable on this guest (no target HW/malicious device). Fix validated structurally: git apply --check OK + full kernel build rc=0 (-Werror).
git apply --check findings/poc/DF-2488/fix.diff -> OK. Combined kernel build: 'NK_DONE rc=0'. No runtime before/after possible (HW-gated).
Confirmed kernel references
Detail
Exploit chain
none — valid hard blocker (driver/device path dead at runtime on this guest: no target HBA / no malicious device / no removable media). No unprivileged->root path.
Evidence (decisive lines)
kldstat -> kernel/ehci/xhci only (no target driver); pciconf -l -> PIIX3 IDE + virtio only (no AHCI/NVMe/AdvanSys HBA); camcontrol devlist -> only <QEMU QEMU DVD-ROM>; ls /dev/<target> -> No such file. Source confirmed at cited lines.
PoC changes
Created findings/poc/DF-2488/{VERDICT.md,fix.diff,env.txt,build.sh,run.sh,manifest.json,fix_build.log}. No PoC source (HW-gated).
Verified recommended fix
Defense-in-depth fix.diff adds the validation/bounds check closing the cited path (see findings/poc/DF-2488/fix.diff; git apply --check OK).
Verdict
NOT REPRODUCED (HW/trigger-gated on this guest). The bug is REAL in source (traced line-by-line): nata ad_describe stack buffer overflow via unbounded index() on non-NUL-terminated ATA IDENTIFY model. Gate confirmed via kldstat (target driver not loaded; only kernel+ehci+xhci), pciconf -l (no target HBA — only PIIX3 IDE atapci0 + virtio), camcontrol devlist (only QEMU DVD-ROM), and ls /dev (no target disk/tape/fd/nvme nodes). The benign QEMU devices cannot produce the malicious device responses the bugs require.
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