Hi Bruce, hi Greg,
On Sun, Dec 12, 2021 at 02:11:30PM +0100, gregkh@linuxfoundation.org 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@vger.kernel.org.
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?
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@redhat.com 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@vger.kernel.org Signed-off-by: J. Bruce Fields bfields@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [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@debian.org --- 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); }