btrfs: reinitialize delayed ref list after deleting it from the list

At insert_delayed_ref() if we need to update the action of an existing
ref to BTRFS_DROP_DELAYED_REF, we delete the ref from its ref head's
ref_add_list using list_del(), which leaves the ref's add_list member
not reinitialized, as list_del() sets the next and prev members of the
list to LIST_POISON1 and LIST_POISON2, respectively.

If later we end up calling drop_delayed_ref() against the ref, which can
happen during merging or when destroying delayed refs due to a transaction
abort, we can trigger a crash since at drop_delayed_ref() we call
list_empty() against the ref's add_list, which returns false since
the list was not reinitialized after the list_del() and as a consequence
we call list_del() again at drop_delayed_ref(). This results in an
invalid list access since the next and prev members are set to poison
pointers, resulting in a splat if CONFIG_LIST_HARDENED and
CONFIG_DEBUG_LIST are set or invalid poison pointer dereferences
otherwise.

So fix this by deleting from the list with list_del_init() instead.

Fixes: 1d57ee941692 ("btrfs: improve delayed refs iterations")
CC: stable@vger.kernel.org # 4.19+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index 115b90d29b1d8e84706b763f3fc589fbf38b4885..65d841d7142c0765e1c7c612ac15a3c94ad52ac1 100644 (file)
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -649,7 +649,7 @@ static bool insert_delayed_ref(struct btrfs_trans_handle *trans,
                                              &href->ref_add_list);
                        else if (ref->action == BTRFS_DROP_DELAYED_REF) {
                                ASSERT(!list_empty(&exist->add_list));
-                               list_del(&exist->add_list);
+                               list_del_init(&exist->add_list);
                        } else {
                                ASSERT(0);
                        }