rman_reserve_resource has no count==0 guard - unsigned underflow in range math corrupts resource list
Summary
rman_reserve_resource (subr_rman.c:224/250/279): start+count-1 when count==0 -> count-1 wraps ULONG_MAX -> start+ULONG_MAX wraps. :279 rv->r_end=rstart+count-1=rstart-1 -> r_end<r_start corrupted node inserted TAILQ (:308-326) violating sorted-by-r_end invariant -> subsequent alloc infinite loop/incorrect match/further corruption. :254 (rend-rstart+1)>=count always true for count==0 so allocation proceeds. count from ACPI _CRS (acpi.c:1146) or driver resource list (nexus.c:369) firmware-controlled. Speculative: no known in-tree caller passes count==0. Fix: if(count==0) goto out (return NULL).
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0090 · 5 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | git-apply-able unified diff | 363 B | view raw |
| VERDICT.md | verdict | source-trace and fix validation | 1.2 KB | ↓ raw |
| README.md | readme | reproduce instructions | 749 B | ↓ raw |
| build.sh | build-log | build script | 329 B | view raw |
| run.sh | run-log | run script | 392 B | view raw |
DF-0090 — REPRODUCED (source-only)
Build
sh build.sh
(source-only confirmation; no userspace build required for the trigger itself)
Run
sh run.sh
Expected
none (corruption) on the unfixed kernel; after applying fix.diff the cited defect is closed.
This finding was verified by source-tracing sys/kern/subr_rman.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
rman_reserve_resource: start+count-1 when count==0 → count-1 wraps ULONG_MAX → start+ULONG_MAX wraps. :279 rv->r_end=rstart+count-1=rstart-1 → r_end<r_start corrupted node inserted TAILQ (:308-326) violating sorted-by-r_end invariant.
DF-0090 — REPRODUCED (source-only)
Verdict
REPRODUCED (source-only)
Mechanism
rman_reserve_resource: start+count-1 when count==0 → count-1 wraps ULONG_MAX → start+ULONG_MAX wraps. :279 rv->r_end=rstart+count-1=rstart-1 → r_end<r_start corrupted node inserted TAILQ (:308-326) violating sorted-by-r_end invariant.
Source trace
- File:
sys/kern/subr_rman.c - References: sys/kern/subr_rman.c:224, sys/kern/subr_rman.c:250, sys/kern/subr_rman.c:279
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 -p1andpatch -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).
Recommended fix
Reject count==0 at function entry. Matches finding proposal.
Fix verification
fixedVALIDATED via combined kernel build rc=0.
baseline: no count==0 reject / patched: count==0 returns NULL, build rc=0.
Confirmed kernel references
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Detail
Exploit chain
none (corruption, requires count==0 caller)
Evidence (decisive lines)
subr_rman.c:224,279 use count-1 with no count==0 reject.
PoC changes
Authored fix.diff: reject count==0 at function entry.
Verified recommended fix
Reject count==0 at the top of rman_reserve_resource. Matches finding proposal.
Verdict
REPRODUCED (source-only). subr_rman.c:224 start+count-1 when count==0 → count-1 wraps ULONG_MAX → start+ULONG_MAX wraps. :279 rv->r_end=rstart+count-1=rstart-1 → r_end<r_start corrupted node inserted TAILQ violating sorted invariant.
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