On Thu, Dec 16, 2021 at 3:05 PM Salvatore Bonaccorso <carnil@xxxxxxxxxx> wrote:
> On Sun, Dec 12, 2021 at 02:11:30PM +0100, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> > The patch below does not apply to the 4.19-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@xxxxxxxxxxxxxxx>.
>
> Unless I'm completely wrong this only does not apply to the older
> series because in 5.6-rc1 we had 20b7d86f29d3 ("nfsd: use boottime for
> lease expiry calculation") soe there is a minor context change in one
> hunk.
>
> Attached is a patch accounting for that, Bruce is this okay?
Yes, this looks fine to me. Thank you!
--b.
> This would apply as well back on top of v4.9.293.
>
> Regards,
> Salvatore
>
> From eeeaf376a2efabdad46ce03516552f4290949834 Mon Sep 17 00:00:00 2001
> From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
> Date: Mon, 29 Nov 2021 15:08:00 -0500
> Subject: [PATCH] nfsd: fix use-after-free due to delegation race
>
> commit 548ec0805c399c65ed66c6641be467f717833ab5 upstream.
>
> A delegation break could arrive as soon as we've called vfs_setlease. A
> delegation break runs a callback which immediately (in
> nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we
> then exit nfs4_set_delegation without hashing the delegation, it will be
> freed as soon as the callback is done with it, without ever being
> removed from del_recall_lru.
>
> Symptoms show up later as use-after-free or list corruption warnings,
> usually in the laundromat thread.
>
> I suspect aba2072f4523 "nfsd: grant read delegations to clients holding
> writes" made this bug easier to hit, but I looked as far back as v3.0
> and it looks to me it already had the same problem. So I'm not sure
> where the bug was introduced; it may have been there from the beginning.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> [Salvatore Bonaccorso: Backport for context changes to versions which do
> not have 20b7d86f29d3 ("nfsd: use boottime for lease expiry
> calculation")]
> Signed-off-by: Salvatore Bonaccorso <carnil@xxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 655079ae1dd1..dfb2a790efc1 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -975,6 +975,11 @@ hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
> return 0;
> }
>
> +static bool delegation_hashed(struct nfs4_delegation *dp)
> +{
> + return !(list_empty(&dp->dl_perfile));
> +}
> +
> static bool
> unhash_delegation_locked(struct nfs4_delegation *dp)
> {
> @@ -982,7 +987,7 @@ unhash_delegation_locked(struct nfs4_delegation *dp)
>
> lockdep_assert_held(&state_lock);
>
> - if (list_empty(&dp->dl_perfile))
> + if (!delegation_hashed(dp))
> return false;
>
> dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
> @@ -3912,7 +3917,7 @@ static void nfsd4_cb_recall_prepare(struct nfsd4_callback *cb)
> * queued for a lease break. Don't queue it again.
> */
> spin_lock(&state_lock);
> - if (dp->dl_time == 0) {
> + if (delegation_hashed(dp) && dp->dl_time == 0) {
> dp->dl_time = get_seconds();
> list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
> }
> --
> 2.34.1
>
