drbd: fix potential access after free
Occasionally, if we disconnect, we triggered this assert:
block drbd7: ASSERT FAILED tl_hash[27] == c30b0f04, expected NULL
hlist_del() happens only on master bio completion.
We used to wait for pending IO to complete before freeing tl_hash
on disconnect. We no longer do so, since we learned to "freeze"
IO on disconnect.
If the local disk is too slow, we may reach C_STANDALONE early,
and there are still some requests pending locally when we call
drbd_free_tl_hash().
If we now free the tl_hash, and later the local IO completion completes
the master bio, which then does hlist_del() and clobbers freed memory.
Do hlist_del_init() and hlist_add_fake() before kfree(tl_hash),
so the hlist_del() on master bio completion is harmless.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index ea4836e..83d9913 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -3801,11 +3801,18 @@
mdev->ee_hash = NULL;
mdev->ee_hash_s = 0;
- /* paranoia code */
- for (h = mdev->tl_hash; h < mdev->tl_hash + mdev->tl_hash_s; h++)
- if (h->first)
- dev_err(DEV, "ASSERT FAILED tl_hash[%u] == %p, expected NULL\n",
- (int)(h - mdev->tl_hash), h->first);
+ /* We may not have had the chance to wait for all locally pending
+ * application requests. The hlist_add_fake() prevents access after
+ * free on master bio completion. */
+ for (h = mdev->tl_hash; h < mdev->tl_hash + mdev->tl_hash_s; h++) {
+ struct drbd_request *req;
+ struct hlist_node *pos, *n;
+ hlist_for_each_entry_safe(req, pos, n, h, collision) {
+ hlist_del_init(&req->collision);
+ hlist_add_fake(&req->collision);
+ }
+ }
+
kfree(mdev->tl_hash);
mdev->tl_hash = NULL;
mdev->tl_hash_s = 0;