Re: [PATCH] mm: mmap_lock: fix use-after-free race and css ref leak in tracepoints

[Tejun Heo]

Hello,

On Wed, Dec 02, 2020 at 03:23:57PM -0800, Shakeel Butt wrote:
> > There've been some changes to cgroup ids recently and now cgroup id, ino and
> > its file_handle are all compatible. On 64bit ino machines, they're all the
> > same and won't be reused. On 32bit ino machines, the lower 32bit of full id
> > is used as ino. ino may be reused but not the full 64bit id.
> 
> __kernfs_new_node() is using idr_alloc_cyclic() which will return
> 32bit ID. If I am understanding this correctly the full ID is
> generated similarly for 32bit and 64bit machines but for 64bit
> machines the whole ID is inode number while on 32bit machines the
> lower 32bits contains the inode number. Is that correct?

Yes, that's correct.

Thanks.

-- 
tejun