пн, 9 дек. 2019 г. в 20:48, Steve French <smfrench@gmail.com>:
>
> Fix refcount underflow warning when unmounting to servers which didn't grant
> directory leases.
>
> [  301.680095] refcount_t: underflow; use-after-free.
> [  301.680192] WARNING: CPU: 1 PID: 3569 at lib/refcount.c:28
> refcount_warn_saturate+0xb4/0xf3
> ...
> [  301.682139] Call Trace:
> [  301.682240]  close_shroot+0x97/0xda [cifs]
> [  301.682351]  SMB2_tdis+0x7c/0x176 [cifs]
> [  301.682456]  ? _get_xid+0x58/0x91 [cifs]
> [  301.682563]  cifs_put_tcon.part.0+0x99/0x202 [cifs]
> [  301.682637]  ? ida_free+0x99/0x10a
> [  301.682727]  ? cifs_umount+0x3d/0x9d [cifs]
> [  301.682829]  cifs_put_tlink+0x3a/0x50 [cifs]
> [  301.682929]  cifs_umount+0x44/0x9d [cifs]
>
> Fixes: 72e73c78c446 ("cifs: close the shared root handle on tree disconnect")
>
> Signed-off-by: Steve French <stfrench@microsoft.com>
> Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
> Reviewed-by: Aurelien Aptel <aaptel@suse.com>
> Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
> Reported-and-tested-by: Arthur Marsh <arthur.marsh@internode.on.net>
>
> --
> Thanks,
>
> Steve

Looking at this more, I think that the fact that the handle is valid
doesn't mean that it has a directory lease. So, I think we need to
track that fact separately. I coded a quick follow-on fix (untested)
to describe my idea - see the attached patch.

Thoughts?

--
Best regards,
Pavel Shilovsky