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The hex dump shows the same pattern btw: > > - obj1 struct file @ ffff88812811f9c0, obj2 its LSM blob > - obj3 iommufd_ctx @ ffff88811161cd80, first word = ffff88812811f9c0 → ictx->file is obj1 > - obj5 xa_node, its ->array = ffff88811161cd88 = &ictx->objects > - obj4 iommufd_object: shortterm_users=1, users=1, type=4, id=1 → the IOAS with ioas_id == 1 from the repro > - obj6 iopt_pages, kref == 1 > > Likely caused by f4986a72d6e4 ("iommufd: Add IOMMU_IOAS_MAP_FILE") > > Afaic,t, this should either reject based on file->f_op == &iommufd_fops. > But iiuc there's other cycles that can be formed. > For example, via a vfio device fd that's bound to the iommufd. It holds an iommufd_ctx reference via iommufd_ctx_from_fd(). > So mapping a bound but unattached vfio fd builds the same cycle. > > So probably this should do validation what type of file can actually be > used like shmem and hugepage file. Oh.. This is a bit of a pain because we rely on memfd_pin_folios() to determine if the file is acceptable or not. I prefer to keep that logic contained within the mm side. The issue is we don't always call memfd_pin_folios() inside the first system call. A normal user would, but syzkaller has arranged something a bit weird and out of order. So we need to figure out some validation to run before the mapping step.. Thanks, Jason