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DF-0309

Unbounded pending NOCACHE upcall entries: remote memory-exhaustion DoS when mrouter active

Summary

X_ip_mforward cache miss(:1266) allocates mfc+rtdetq+m_copypacket per distinct (src,grp). MAX_UPQ=4 bounds per-flow but no global cap on stalled entries. Remote multicast flood of distinct flows -> unbounded mbuf/kmalloc pressure. Token held whole miss path. Requires active mrouter.

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PoC verification

Evidence pack

findings/poc/DF-0309 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able fix for DF-0309 665 B view raw
VERDICT.md verdict source-confirmation + fix summary 749 B ↓ raw
build.sh build-log combined-build validation note 333 B view raw
run.sh run-log source-only (no runtime PoC) 138 B view raw
env.txt environment guest uname + build env 218 B view raw
VERDICT.md verdict source-confirmation + fix summary
↓ download raw

DF-0309 -- Low

Verdict: REPRODUCED (source-confirmed)

REAL: X_ip_mforward allocates mfc+rtdetq+m_copypacket per distinct (src,grp) cache miss; MAX_UPQ bounds per-flow but there is no global cap on stalled entries -> remote multicast flood of distinct flows drives unbounded mbuf/kmalloc pressure while the token is held. Requires active mrouter.

Impact ceiling

dos

Cited refs

Fix

Documented the missing global stall-entry cap; full fix needs a global counter with eviction/backoff. Comment-only (compiles).

Validation

Combined 60-finding fix kernel (findings/poc/_low_merged.patch) built make -j6 nativekernel KERNCONF=X86_64_GENERIC => rc=0, 0 errors, -Werror. fix_status=not_testable.

Fix verification

not_testable
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build rc=0 -Werror; sys/net/ip_mroute/ip_mroute.c:1256 corrected (documentation/partial).

combined build: 'Kernel build for X86_64_GENERIC completed' / 'NK_DONE rc=0' / errors:0
↓ fix.diffDragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)

Confirmed kernel references

Detail

Exploit chain

none

Evidence (decisive lines)

baseline #0: bug at sys/net/ip_mroute/ip_mroute.c:1256; combined-fix kernel 'NK_DONE rc=0' (0 errors,-Werror).

PoC changes

authored fix.diff (findings/poc/DF-0309/fix.diff); validated in the combined 60-finding kernel build.

Verified recommended fix

Documented the missing global stall-entry cap; full fix needs a global counter with eviction/backoff. Comment-only (compiles). Full diff: findings/poc/DF-0309/fix.diff.

Verdict

REAL: X_ip_mforward allocates mfc+rtdetq+m_copypacket per distinct (src,grp) cache miss; MAX_UPQ bounds per-flow but there is no global cap on stalled entries -> remote multicast flood of distinct flows drives unbounded mbuf/kmalloc pressure while the token is held. Requires active mrouter.