Summary

tpm.c:1273 n = MIN(sizeof(buf), uio->uio_resid) -> n=0 for write(fd,buf,0). 1284 tpm_tis12_write(sc, buf, 0) NO early return. 820-825 while (cnt < len-1) where cnt is size_t and len is int; len=0 -> len-1=-1 -> promoted to SIZE_MAX -> loop unbounded. *p++ derefs uninitialized stack buf[TPM_BUFSIZ=1024] writing to TPM_DATA FIFO. Over-reads kernel stack -> info leak to TPM hardware + potential panic on guard page. /dev/tpm mode 0600 root:wheel. Fix: if(len<=0) return EINVAL in tpm_tis12_write + if(uio_resid==0) return 0 in tpmwrite.

PoC verification

Evidence pack

findings/poc/DF-1597 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	337 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-1597 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: tpm.c:1273 n = MIN(sizeof(buf), uio->uio_resid) -> n=0 for write(fd,buf,0). 1284 tpm_tis12_write(sc, buf, 0) NO early return. 820-825 while (cnt < len-1) where cnt is size_t and len is int; len=0 -> l

Citation: sys/dev/crypto/tpm/tpm.c:821-1284

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: size_t cnt < int len-1 wraps to SIZE_MAX when len=0 (tpm.c:807-822)

Verified recommended fix

Source-confirmed: size_t cnt < int len-1 wraps to SIZE_MAX when len=0 (tpm.c:807-822)

Verdict