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DF-0061

Relocation r_offset never bounds-checked against module size (DF-0042 analogue, wild write)

Summary

relocate_file (link_elf.c:714-767): no r_offset<lf->size check before elf_reloc; arch helper elf_machdep.c:90 where=relocbase+r_offset *where=val -> crafted r_offset yields wild write of symbol-resolved value to ef->address+r_offset past module buffer. Same gap in link_elf_reloc_local (:1024-1051). DF-0042 analogue (link_elf_obj.c). Root-only defense-in-depth.

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PoC verification

Evidence pack

findings/poc/DF-0061 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able unified diff 879 B view raw
VERDICT.md verdict source-trace and fix validation 1.2 KB ↓ raw
README.md readme reproduce instructions 738 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-0061 — 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

relocate_file dispatches each rel/rela to elf_reloc with no r_offsetsize check; arch helper writes *(relocbase + r_offset). Crafted r_offset yields wild write of symbol-resolved value past the module buffer.

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

DF-0061 — REPRODUCED (source-only, root-only kldload)

Verdict

REPRODUCED (source-only, root-only kldload)

Mechanism

relocate_file dispatches each rel/rela to elf_reloc with no r_offsetsize check; arch helper writes *(relocbase + r_offset). Crafted r_offset yields wild write of symbol-resolved value past the module buffer.

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).

Skip relocations whose r_offset >= lf->size. Matches finding proposal.

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined kernel build rc=0.

baseline: no r_offset check / patched: r_offset >= lf->size skip, 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:718,732 no r_offset<lf->size check.

PoC changes

Authored fix.diff: skip rel/rela entries whose r_offset >= lf->size.

Verified recommended fix

Skip relocations whose r_offset >= lf->size in relocate_file rel and rela loops. Matches finding proposal.

Verdict

REPRODUCED (source-only, root-only). link_elf.c:714-767 relocate_file dispatches each rel/rela to elf_reloc with no r_offsetsize check; arch helper writes *(relocbase + r_offset). Crafted r_offset wild-writes past module buffer.