ext2_reallocblks feeds unclamped attacker-controlled pref (crafted i_db[]/indirect values via ext2_blkpref) into dtog() as the cg index — OOB heap reads of e2fs_gd[]/e2fs_maxcluster[]/e2fs_clustersum[] and wild device I/O (root-sysctl-gated)
Summary
ext2_blkpref returns raw le32toh(bap[tmp]) values from crafted on-disk block maps (:710-712). Every other consumer funnels them through ext2_alloc's 'bpref >= bcount -> 0' clamp (:130), but ext2_reallocblks:302 calls ext2_hashalloc(ip, dtog(fs, pref), pref, ...) directly: pref up to 0xFFFFFFFF gives cg up to ~524287, far beyond gcount, indexing fs->e2fs_maxcluster[cg] (:1146), fs->e2fs_gd[cg] (:1151) and fs->e2fs_clustersum[cg] out of bounds - wild kernel heap reads whose results then steer bread/bdwrite device offsets. Gated behind vfs.ext2fs.doreallocblks != 0 (default 0, root-writable sysctl) and contigsumsize > 0, hence Low. Verification skipped (privileged-configuration gate). Fix: clamp pref >= bcount -> 0 (mirroring :130). [VERIFIED pass2: vn dscheck rejects negative device offsets before reallocblks consumes pref - OOB index unobservable via this route; sysctl gate default-0 confirmed]
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-3065 · 7 files| File | Type | Description | Size | |
|---|---|---|---|---|
| README.md | — | 301 B | ↓ raw | |
| VERDICT.md | — | 1.3 KB | ↓ raw | |
| env.txt | — | 248 B | view raw | |
| fix.diff | — | 105 B | view raw | |
| manifest.json | — | 564 B | view raw | |
| run.log | — | 244 B | view raw | |
| verdict.json | — | 1.4 KB | view raw |
DF-3065 - ext2_reallocblks feeds unclamped crafted pref into dtog() -> OOB reads of e2fs arrays
Severity Low | verdict: not_reproduced | impact: none
Reproduce
No runnable PoC on this rig (see VERDICT.md for why).
See VERDICT.md for the full narrative and run.log for the decisive output.
DF-3065 verification
Kernel: DragonFly dfbsd 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64
Attempted with the gate open: vfs.ext2fs.doreallocblks set to 1 (default 0, root-only sysctl confirmed), crafted ext2 image with i_block[0]=0xFFFFFFFF and i_block[1]=0x7FFFFFFF via debugfs. The wild block numbers short-circuit earlier: reads/writes of the crafted file fail with the vn driver rejecting negative device offsets (dscheck(vn2): negative bio_offset -1024 in dmesg; cat returns EINVAL, dd writes 0 bytes) before ext2_reallocblks consumes the garbage pref. The claimed OOB index of e2fs_maxcluster/e2fs_gd could not be observed; the root-sysctl gate (default off) plus this early rejection keep it unreachable from the crafted-image route on this rig.
Kernel references
Fix
See fix.diff.
Fix status (batch validation)
Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.
Fix verification
not_testableConfirmed kernel references
Detail
Evidence (decisive lines)
VERDICT.md + run.log + sources
PoC changes
none
Verified recommended fix
diff: clamp pref in ext2_reallocblks exactly like ext2_alloc:130 (bpref >= bcount -> 0) before dtog().
Verdict
Attempted with the gate open: vfs.ext2fs.doreallocblks set to 1 (default 0, root-only sysctl confirmed), crafted ext2 image with i_block[0]=0xFFFFFFFF and i_block[1]=0x7FFFFFFF via debugfs. The wild block numbers short-circuit earlier: reads/writes of the crafted file fail with the vn driver rejecting negative device offsets (dscheck(vn2): negative bio_offset -1024 in dmesg; cat returns EINVAL, dd writes 0 bytes) before ext2_reallocblks consumes the garbage pref. The claimed OOB index of e2fs_maxcluster/e2fs_gd could not be observed; the root-sysctl gate (default off) plus this early rejection keep it unreachable from the crafted-image route on this rig.
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