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hfsplus: return error when node already exists in hfs_bnode_create

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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.

Reported-by: syzbot+1c8ff72d0cd8a50dfeaa@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=1c8ff72d0cd8a50dfeaa
Link: https://lore.kernel.org/all/784415834694f39902088fa8946850fc1779a318.camel@ibm.com/
Fixes: 634725a929 ("[PATCH] hfs: cleanup HFS+ prints")
Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/20251229204938.1907089-1-shardul.b@mpiricsoftware.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
This commit is contained in:
Shardul Bankar 2025-12-30 02:19:38 +05:30 • committed by Viacheslav Dubeyko
parent b226804532
commit d8a73cc46c
1 changed files with 1 additions and 1 deletions
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2
fs/hfsplus/bnode.c
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@ -629,7 +629,7 @@ struct hfs_bnode *hfs_bnode_create(struct hfs_btree *tree, u32 num)
if (node) {
pr_crit("new node %u already hashed?\n", num);
WARN_ON(1);
return node;
return ERR_PTR(-EEXIST);
}
node = __hfs_bnode_create(tree, num);
if (!node)