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DF-0058

Unbounded sh_link to symstrindex causes heap OOB read (DF-0040 analogue, worse: no check at all)

Summary

link_elf_load_file section scan (link_elf.c:601-620): symstrindex=shdr[i].sh_link (Elf64_Word) set with NO bounds check vs e_shnum (DF-0040 in link_elf_obj.c had off-by-one >; this file has zero check); then shdr[symstrindex].sh_size/sh_offset deref at :612/:620 is OOB if symstrindex>=e_shnum. Root-only defense-in-depth.

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PoC verification

Evidence pack

findings/poc/DF-0058 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able unified diff 400 B view raw
VERDICT.md verdict source-trace and fix validation 1.2 KB ↓ raw
README.md readme reproduce instructions 725 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-0058 — 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

link_elf_load_file section scan: symstrindex=shdr[i].sh_link (Elf64_Word) set with NO bounds check vs e_shnum. shdr[symstrindex].sh_size/sh_offset deref at :612/:620 is OOB if symstrindex >= e_shnum.

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

DF-0058 — REPRODUCED (source-only, root-only kldload)

Verdict

REPRODUCED (source-only, root-only kldload)

Mechanism

link_elf_load_file section scan: symstrindex=shdr[i].sh_link (Elf64_Word) set with NO bounds check vs e_shnum. shdr[symstrindex].sh_size/sh_offset deref at :612/:620 is OOB if symstrindex >= e_shnum.

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).

Guard shdr[i].sh_link < hdr->e_shnum before setting symstrindex. Matches finding proposal.

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined kernel build rc=0.

baseline: no sh_link bounds check / patched: < e_shnum guard, 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:604 no sh_link<e_shnum guard.

PoC changes

Authored fix.diff: guard sh_link < e_shnum before setting symstrindex.

Verified recommended fix

if (shdr[i].sh_link < hdr->e_shnum) symstrindex = shdr[i].sh_link. Matches finding proposal.

Verdict

REPRODUCED (source-only, root-only). link_elf.c:604 sets symstrindex = shdr[i].sh_link (Elf64_Word) with NO bounds check vs e_shnum; :612 derefs shdr[symstrindex] OOB if symstrindex >= e_shnum.