In the Linux kernel, the following vulnerability has been resolved:

hfsplus: return error when node already exists in hfs_bnode_create

When hfs_bnode_create() finds that a node is already hashed (which should
not happen in normal operation), it currently returns the existing node
without incrementing its reference count. This causes a reference count
inconsistency that leads to a kernel panic when the node is later freed
in hfs_bnode_put():

kernel BUG at fs/hfsplus/bnode.c:676!
BUG_ON(!atomic_read(&node->refcnt))

This scenario can occur when hfs_bmap_alloc() attempts to allocate a node
that is already in use (e.g., when node 0's bitmap bit is incorrectly
unset), or due to filesystem corruption.

Returning an existing node from a create path is not normal operation.

Fix this by returning ERR_PTR(-EEXIST) instead of the node when it's
already hashed. This properly signals the error condition to callers,
which already check for IS_ERR() return values.