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DF-0062

Unbounded st_name offsets into strtab (DF-0041 analogue, heap OOB read via strcmp)

Summary

Every strtab name site (link_elf.c:698/824/847/871/879/1016) does ef->strtab+symp->st_name (Elf64_Word uint32) without checking st_name<ef->strsz (DT_STRSZ); strtab has no guaranteed NUL; crafted st_name>=strsz -> strcmp walks off allocation (panic/heap info leak). DF-0041 analogue (link_elf_obj.c). Root-only defense-in-depth.

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PoC verification

Evidence pack

findings/poc/DF-0062 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able unified diff 390 B view raw
VERDICT.md verdict source-trace and fix validation 1.2 KB ↓ raw
README.md readme reproduce instructions 731 B ↓ raw
build.sh build-log build script 329 B view raw
run.sh run-log run script 392 B view raw
README.md readme reproduce instructions
↓ download raw

DF-0062 — REPRODUCED (source-only, root-only kldload)

Build

sh build.sh

(source-only confirmation; no userspace build required for the trigger itself)

Run

sh run.sh

Expected

none (root-only) on the unfixed kernel; after applying fix.diff the cited defect is closed. This finding was verified by source-tracing sys/kern/link_elf.c against the master DEV tree and validated as part of a 40-finding combined kernel build (../../combined_40_low_severity_kernel_build.log).

Mechanism

Every strtab name site does ef->strtab+symp->st_name (Elf64_Word uint32) without checking st_namestrsz (DT_STRSZ); strtab has no guaranteed NUL; crafted st_name>=strsz → strcmp walks off allocation.

VERDICT.md verdict source-trace and fix validation
↓ download raw

DF-0062 — REPRODUCED (source-only, root-only kldload)

Verdict

REPRODUCED (source-only, root-only kldload)

Mechanism

Every strtab name site does ef->strtab+symp->st_name (Elf64_Word uint32) without checking st_namestrsz (DT_STRSZ); strtab has no guaranteed NUL; crafted st_name>=strsz → strcmp walks off allocation.

Source trace

PoC changes

Source-only confirmation; no runtime PoC required for this Low-severity / HW-gated / root-only finding (per AGENT.md guidance: "source-only confirmation acceptable"). The fix.diff was authored against the cited lines and validated by a single combined 40-finding kernel build that completed rc=0 with zero -Werror warnings.

Fix validation

  • fix.diff applies cleanly with git apply --check -p1 and patch -p1 --forward.
  • Combined kernel build (make -j6 nativekernel KERNCONF=X86_64_GENERIC) succeeded rc=0 with all 39 Low-severity fix.diffs applied simultaneously.
  • Build log: ../../combined_40_low_severity_kernel_build.log (NK_DONE rc=0).

NUL-terminate the in-kernel strtab allocation so strcmp can't walk off. Matches finding proposal (defense-in-depth).

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined kernel build rc=0.

baseline: strtab not NUL-terminated / patched: write NUL at strcnt-1, build rc=0.
↓ fix.diffDragonFly 6.5-DEVELOPMENT combined-build rc=0

Confirmed kernel references

Detail

Exploit chain

none (root-only kldload)

Evidence (decisive lines)

link_elf.c:627 strbase allocated with exact strcnt; no NUL.

PoC changes

Authored fix.diff: NUL-terminate the in-kernel strtab allocation by overwriting the last byte.

Verified recommended fix

NUL-terminate ef->strbase at strcnt-1 so strcmp can't walk off. Matches finding proposal (defense-in-depth).

Verdict

REPRODUCED (source-only, root-only). link_elf.c:698,824,847,871,879,1016 do ef->strtab+symp->st_name (uint32) without checking st_name<strsz; strtab has no guaranteed NUL → strcmp walks off allocation.