Hi,

This series addresses btree bitmap corruption around node 0 in HFS and
HFS+.

Node 0 is the reserved btree header node. If the on-disk bitmap ever
presents node 0 as free, the filesystem is already corrupted and should
not continue normal allocation from that state.

The series does two things:

  1. Port the existing HFS+ style mount-time node 0 bitmap validation to
     HFS, so HFS detects the corrupted btree map earlier and forces the
     filesystem read-only.

  2. Harden the HFS and HFS+ btree allocators so that attempts to
     allocate node 0 are treated as bitmap corruption. Instead of
     continuing into the reserved header node and later tripping the
     "new node 0 already hashed?" warning, the allocator now emits a
     repair hint, forces the filesystem read-only, and aborts the
     allocation.

This keeps the existing warning as a last-resort invariant check, while
moving the actual corruption handling to earlier and more appropriate
control points.

Patch 1 ports the mount-time validation to HFS.
Patch 2 adds the runtime allocator guard to both HFS and HFS+.

Comments are welcome.


Tao Yu (2):
  hfs: detect node 0 btree map corruption at mount time
  hfs/hfsplus: stop btree allocators from reusing node 0

 fs/hfs/btree.c     | 71 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/hfsplus/btree.c | 11 +++++++
 2 files changed, 82 insertions(+)


Thanks,
Tao
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2.34.1