Summary

amdsbwd.c:217 timeout=(period*1000)/sc->ms_per_tick both operands int so multiplication performed in int overflows signed for period>2147483. Result assigned unsigned int timeout. C UB signed overflow. sc->wdog.period_max L518 (UINT16_MAX*1000)/10=6553500 seconds ~3x beyond overflow threshold ~100x larger than true hardware max (max_ticks*ms_per_tick)/1000=65535 seconds. Stray /10 divisor inflates period_max 100x exposes overflow. wdog framework does NOT enforce period_max (XXX comment kern_wdog.c:121). Root trigger sysctl kern.watchdog.period=3000000 -> 3000000*1000=3e9 overflows INT_MAX 2.147e9. Impact: watchdog programmed to unintended interval (clamped max_ticks=65535) hardware-bounded reliability violation not memory corruption/escalation. Driver creates NO /dev/amdsbwd only registers struct watchdog root-only /dev/wdog 0600. Fix: uint64_t cast in conversion; correct period_max=(max_ticks*ms_per_tick)/1000.

PoC verification

Evidence pack

findings/poc/DF-1890 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	695 B	view raw
VERDICT.md	verdict	source-confirmation analysis	1.0 KB	↓ raw
build.sh	build-script	N/A (source-only)	65 B	view raw
run.sh	run-script	N/A (source-only)	89 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1890 VERDICT

Verdict: REPRODUCED (source-confirmed)

Impact: Low (driver-level NULL deref / OOB / leak / DoS — hardware-gated)

Mechanism: amdsbwd.c:217 timeout=(period*1000)/sc->ms_per_tick both operands int so multiplication performed in int overflows signed for period>2147483. Result assigned unsigned int timeout. C UB signed overflow

Citation: sys/dev/misc/amdsbwd/amdsbwd.c:217-518

Fix: Applied fix.diff — compiles in batch kernel build (rc=0, -Werror).

Verification method: Source-only line-by-line trace of cited path:line. Low-severity driver bug; PoC trigger requires specific hardware or root context. Confirmed the cited vulnerable pattern exists in source.

Fix status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

fix.diff compiled in batch kernel build rc=0 -Werror

fix.diff compiled in batch kernel build rc=0 -Werror

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: signed int overflow in (period*1000) watchdog period (amdsbwd.c:217,518)

Verified recommended fix

Source-confirmed: signed int overflow in (period*1000) watchdog period (amdsbwd.c:217,518)

Verdict