Re: [PATCH v2] NFSD: fix use-after-free on source server when doing inter-server copy

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2022-08-01 at 18:52 -0700, Dai Ngo wrote:
> Use-after-free occurred when the laundromat tried to free expired
> cpntf_state entry on the s2s_cp_stateids list after inter-server
> copy completed. The sc_cp_list that the expired copy state was
> inserted on was already freed.
> 
> When COPY completes, the Linux client normally sends LOCKU(lock_state x),
> FREE_STATEID(lock_state x) and CLOSE(open_state y) to the source server.
> The nfs4_put_stid call from nfsd4_free_stateid cleans up the copy state
> from the s2s_cp_stateids list before freeing the lock state's stid.
> 
> However, sometimes the CLOSE was sent before the FREE_STATEID request.
> When this happens, the nfsd4_close_open_stateid call from nfsd4_close
> frees all lock states on its st_locks list without cleaning up the copy
> state on the sc_cp_list list. When the time the FREE_STATEID arrives the
> server returns BAD_STATEID since the lock state was freed. This causes
> the use-after-free error to occur when the laundromat tries to free
> the expired cpntf_state.
> 
> This patch adds a call to nfs4_free_cpntf_statelist in
> nfsd4_close_open_stateid to clean up the copy state before calling
> free_ol_stateid_reaplist to free the lock state's stid on the reaplist.
> 
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/nfs4state.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 9409a0dc1b76..b99c545f93e4 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1049,6 +1049,9 @@ static struct nfs4_ol_stateid * nfs4_alloc_open_stateid(struct nfs4_client *clp)
>  
>  static void nfs4_free_deleg(struct nfs4_stid *stid)
>  {
> +	struct nfs4_ol_stateid *stp = openlockstateid(stid);
> +
> +	WARN_ON(!list_empty(&stp->st_stid.sc_cp_list));
>  	kmem_cache_free(deleg_slab, stid);
>  	atomic_long_dec(&num_delegations);
>  }
> @@ -1463,6 +1466,7 @@ static void nfs4_free_ol_stateid(struct nfs4_stid *stid)
>  	release_all_access(stp);
>  	if (stp->st_stateowner)
>  		nfs4_put_stateowner(stp->st_stateowner);
> +	WARN_ON(!list_empty(&stp->st_stid.sc_cp_list));
>  	kmem_cache_free(stateid_slab, stid);
>  }
>  
> @@ -6608,6 +6612,7 @@ static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
>  	struct nfs4_client *clp = s->st_stid.sc_client;
>  	bool unhashed;
>  	LIST_HEAD(reaplist);
> +	struct nfs4_ol_stateid *stp;
>  
>  	spin_lock(&clp->cl_lock);
>  	unhashed = unhash_open_stateid(s, &reaplist);
> @@ -6616,6 +6621,8 @@ static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
>  		if (unhashed)
>  			put_ol_stateid_locked(s, &reaplist);
>  		spin_unlock(&clp->cl_lock);
> +		list_for_each_entry(stp, &reaplist, st_locks)
> +			nfs4_free_cpntf_statelist(clp->net, &stp->st_stid);
>  		free_ol_stateid_reaplist(&reaplist);
>  	} else {
>  		spin_unlock(&clp->cl_lock);

Reviewed-by: Jeff Layton <jlayton@kernel.org>