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Message-ID: <ea6d0556198dd6b77f1ab711401ca65bc39e9912.camel@kernel.org>
Subject: Re: [PATCH] NFSD: fix use-after-free on source server when doing
 inter-server copy
From:   Jeff Layton <jlayton@kernel.org>
To:     Dai Ngo <dai.ngo@oracle.com>, chuck.lever@oracle.com,
        olga.kornievskaia@gmail.com
Cc:     linux-nfs@vger.kernel.org
Date:   Mon, 01 Aug 2022 07:47:21 -0400
In-Reply-To: <1659298792-5735-1-git-send-email-dai.ngo@oracle.com>
References: <1659298792-5735-1-git-send-email-dai.ngo@oracle.com>
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On Sun, 2022-07-31 at 13:19 -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.
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/nfs4state.c | 3 +++
>  1 file changed, 3 insertions(+)
>=20
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 9409a0dc1b76..749f51dff5c7 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6608,6 +6608,7 @@ static void nfsd4_close_open_stateid(struct nfs4_ol=
_stateid *s)
>  	struct nfs4_client *clp =3D s->st_stid.sc_client;
>  	bool unhashed;
>  	LIST_HEAD(reaplist);
> +	struct nfs4_ol_stateid *stp;
> =20
>  	spin_lock(&clp->cl_lock);
>  	unhashed =3D unhash_open_stateid(s, &reaplist);
> @@ -6616,6 +6617,8 @@ 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);

Nice catch.

There are a number of places that call free_ol_stateid_reaplist. Is it
really only in nfsd4_close_open_stateid that we need to do this? I
wonder if it would be better to do this inside free_ol_stateid_reaplist
instead so that all of those callers clean up the copy states as well?
--=20
Jeff Layton <jlayton@kernel.org>