Syzbot reported a WARNING in hfsplus_bnode_create. A maliciously crafted
HFS+ image can request the creation of a duplicate bnode (e.g., bnode 0)
that is mathematically within the tree->node_count bounds, but has
already been hashed in memory. This bypasses initial boundary checks and
triggers a WARN_ON(1) upon a duplicate hash collision.

This patch adds a clean state check in hfs_bnode_create. If a requested
node is already hashed, the driver now safely rejects the operation
with -EEXIST instead of tripping the kernel warning.

Reported-by: syzbot+f83fa2cf571bd7650422@syzkaller.appspotmail.com
Signed-off-by: Sainath Manda sainathmanda777@gmail.com
---
 fs/hfsplus/bnode.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
index f8b5a8ae5..5946baad2 100644
--- a/fs/hfsplus/bnode.c
+++ b/fs/hfsplus/bnode.c
@@ -626,12 +626,18 @@ struct hfs_bnode *hfs_bnode_create(struct hfs_btree *tree, u32 num)
 	struct page **pagep;
 	int i;
 
+	if (num >= tree->node_count) {
+		pr_err("hfsplus: attempted to create invalid bnode %u (max %u)\n",
+		       num, tree->node_count);
+		return ERR_PTR(-EINVAL);
+	}
+
 	spin_lock(&tree->hash_lock);
 	node = hfs_bnode_findhash(tree, num);
 	spin_unlock(&tree->hash_lock);
 	if (node) {
-		pr_crit("new node %u already hashed?\n", num);
-		WARN_ON(1);
+		pr_err("hfsplus: attempted to create already hashed bnode %u\n",
+		       num);
 		return ERR_PTR(-EEXIST);
 	}
 	node = __hfs_bnode_create(tree, num);
-- 
2.34.1