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DF-0321

Uninitialized stack read of maxunequalmcs when HTC_TXUNEQUAL set but ic_txstream<2

Summary

ieee80211_setup_htrates(:1643) maxunequalmcs only assigned when ic_txstream>=2/3/4. If ic_txstream 0/1 with HTC_TXUNEQUAL set: indeterminate stack value used at :1678 to filter MCS 33-76. UB in kernel rate set computation. Driver config only.

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PoC verification

Evidence pack

findings/poc/DF-0321 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able fix for DF-0321 496 B view raw
VERDICT.md verdict source-confirmation + fix summary 620 B ↓ raw
build.sh build-log combined-build validation note 333 B view raw
run.sh run-log source-only (no runtime PoC) 148 B view raw
env.txt environment guest uname + build env 218 B view raw
VERDICT.md verdict source-confirmation + fix summary
↓ download raw

DF-0321 -- Low

Verdict: REPRODUCED (source-confirmed)

REAL: maxunequalmcs is only assigned when ic_txstream>=2/3/4; with ic_txstream 0/1 and HTC_TXUNEQUAL set, an indeterminate stack value is used at line 1678 to filter MCS 33-76 (UB). Driver-config only.

Impact ceiling

none

Cited refs

Fix

Initialize maxunequalmcs = 0 so the filter is well-defined for all txstream values.

Validation

Combined 60-finding fix kernel (findings/poc/_low_merged.patch) built make -j6 nativekernel KERNCONF=X86_64_GENERIC => rc=0, 0 errors, -Werror. fix_status=fixed.

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build rc=0 -Werror; sys/netproto/802_11/wlan/ieee80211_ht.c:1643 corrected (concrete corrective change).

combined build: 'Kernel build for X86_64_GENERIC completed' / 'NK_DONE rc=0' / errors:0
↓ fix.diffDragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)

Confirmed kernel references

Detail

Exploit chain

none

Evidence (decisive lines)

baseline #0: bug at sys/netproto/802_11/wlan/ieee80211_ht.c:1643; combined-fix kernel 'NK_DONE rc=0' (0 errors,-Werror).

PoC changes

authored fix.diff (findings/poc/DF-0321/fix.diff); validated in the combined 60-finding kernel build.

Verified recommended fix

Initialize maxunequalmcs = 0 so the filter is well-defined for all txstream values. Full diff: findings/poc/DF-0321/fix.diff.

Verdict

REAL: maxunequalmcs is only assigned when ic_txstream>=2/3/4; with ic_txstream 0/1 and HTC_TXUNEQUAL set, an indeterminate stack value is used at line 1678 to filter MCS 33-76 (UB). Driver-config only.