Hi,
syzbot reported a warning and crash when mounting a corrupted HFS+ image where the on-disk B-tree bitmap has node 0 (header node) marked free. In that case hfs_bmap_alloc() can try to allocate node 0 and reach hfs_bnode_create() with an already-hashed node number.
Patch 1 prevents allocating the reserved header node (node 0) even if the bitmap is corrupted.
Patch 2 follows Slava's review suggestion and changes the "already hashed" path in hfs_bnode_create() to return ERR_PTR(-EEXIST) instead of returning the existing node pointer, so we don't continue in a non-"business as usual" situation.
v2 changes: - Implement Slava's suggestion: return ERR_PTR(-EEXIST) for already-hashed nodes. - Keep the node-0 allocation guard as a minimal, targeted hardening measure.
Reported-by: syzbot+1c8ff72d0cd8a50dfeaa@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?extid=1c8ff72d0cd8a50dfeaa Link: https://lore.kernel.org/all/20251213233215.368558-1-shardul.b@mpiricsoftware...
Shardul Bankar (2): hfsplus: skip node 0 in hfs_bmap_alloc hfsplus: return error when node already exists in hfs_bnode_create
fs/hfsplus/bnode.c | 2 +- fs/hfsplus/btree.c | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-)