Re: [PATCH v3] ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

[Steve French]

I see some AI review comments from Sashiko:
https://sashiko.dev/#/patchset/20260317065253.1743552-1-werner%40verivus.com

On Tue, Mar 17, 2026 at 3:17 AM ChenXiaoSong
<chenxiaosong@xxxxxxxxxxxxxxxx> wrote:
>
> Looks good to me so far. Others can continue the review.
>
> Thanks,
> ChenXiaoSong <chenxiaosong@xxxxxxxxxx>
>
> On 3/17/26 14:52, Werner Kasselman wrote:
> > smb_grant_oplock() has two issues in the oplock publication sequence:
> >
> > 1) opinfo is linked into ci->m_op_list (via opinfo_add) before
> >     add_lease_global_list() is called.  If add_lease_global_list()
> >     fails (kmalloc returns NULL), the error path frees the opinfo
> >     via __free_opinfo() while it is still linked in ci->m_op_list.
> >     Concurrent m_op_list readers (opinfo_get_list, or direct iteration
> >     in smb_break_all_levII_oplock) dereference the freed node.
> >
> > 2) opinfo->o_fp is assigned after add_lease_global_list() publishes
> >     the opinfo on the global lease list.  A concurrent
> >     find_same_lease_key() can walk the lease list and dereference
> >     opinfo->o_fp->f_ci while o_fp is still NULL.
> >
> > Fix by restructuring the publication sequence to eliminate post-publish
> > failure:
> >
> > - Set opinfo->o_fp before any list publication (fixes NULL deref).
> > - Preallocate lease_table via alloc_lease_table() before opinfo_add()
> >    so add_lease_global_list() becomes infallible after publication.
> > - Keep the original m_op_list publication order (opinfo_add before
> >    lease list) so concurrent opens via same_client_has_lease() and
> >    opinfo_get_list() still see the in-flight grant.
> > - Use opinfo_put() instead of __free_opinfo() on err_out so that
> >    the RCU-deferred free path is used.
> >
> > This also requires splitting add_lease_global_list() to take a
> > preallocated lease_table and changing its return type from int to void,
> > since it can no longer fail.
> >
> > Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
> > Fixes: 1dfd062caa16 ("ksmbd: fix use-after-free by using call_rcu() for oplock_info")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Werner Kasselman <werner@xxxxxxxxxxx>



-- 
Thanks,

Steve