Re: [PATCH] nfsd: hold cl_lock in client_has_state()

[Greg KH]

On Fri, Aug 28, 2026 at 12:19:25AM -0400, Cen Zhang (Microsoft Security FORGE Labs) wrote:
> client_has_openowners() walks clp->cl_openowners and reads so_stateids
> without clp->cl_lock. nfs4_put_stateowner() unhashes that openowner under
> cl_lock and then frees it, so a concurrent EXCHANGE_ID with mismatched
> creds can use-after-free the nfs4_openowner.
> 
> BUG: KASAN: slab-use-after-free in client_has_state+0x10a/0x140
>   fs/nfsd/nfs4state.c:3718 client_has_openowners()
>   nfsd4_exchange_id
>   nfsd4_proc_compound
>   nfsd_dispatch
>   svc_process
> 
> Take clp->cl_lock while client_has_state() walks the openowner list.
> 
> Fixes: 4eaea1342507 ("nfsd: improve client_has_state to check for unused openowners")
> Reported-by: Xiang Mei (Microsoft) <xmei5@xxxxxxx>
> Cc: AutonomousCodeSecurity@xxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) <blbllhy@xxxxxxxxx>

Please use your microsoft.com email address, and not a random gmail.com
address.  It's kind of odd that Microsoft would have to rely on Google
to send kernel patches :)

thanks,

greg k-h