padata: add separate cpuhp node for CPUHP_PADATA_DEAD

Removing the pcrypt module triggers this:

  general protection fault, probably for non-canonical
    address 0xdead000000000122
  CPU: 5 PID: 264 Comm: modprobe Not tainted 5.6.0+ #2
  Hardware name: QEMU Standard PC
  RIP: 0010:__cpuhp_state_remove_instance+0xcc/0x120
  Call Trace:
   padata_sysfs_release+0x74/0xce
   kobject_put+0x81/0xd0
   padata_free+0x12/0x20
   pcrypt_exit+0x43/0x8ee [pcrypt]

padata instances wrongly use the same hlist node for the online and dead
states, so __padata_free()'s second cpuhp remove call chokes on the node
that the first poisoned.

cpuhp multi-instance callbacks only walk forward in cpuhp_step->list and
the same node is linked in both the online and dead lists, so the list
corruption that results from padata_alloc() adding the node to a second
list without removing it from the first doesn't cause problems as long
as no instances are freed.

Avoid the issue by giving each state its own node.

Fixes: 894c9ef9780c ("padata: validate cpumask without removed CPU during offline")
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/padata.h b/include/linux/padata.h
index a0d8b41850b2..693cae9bfe66 100644
--- a/include/linux/padata.h
+++ b/include/linux/padata.h
@@ -139,7 +139,8 @@ struct padata_shell {
 /**
  * struct padata_instance - The overall control structure.
  *
- * @node: Used by CPU hotplug.
+ * @cpu_online_node: Linkage for CPU online callback.
+ * @cpu_dead_node: Linkage for CPU offline callback.
  * @parallel_wq: The workqueue used for parallel work.
  * @serial_wq: The workqueue used for serial work.
  * @pslist: List of padata_shell objects attached to this instance.
@@ -150,7 +151,8 @@ struct padata_shell {
  * @flags: padata flags.
  */
 struct padata_instance {
-	struct hlist_node		 node;
+	struct hlist_node		cpu_online_node;
+	struct hlist_node		cpu_dead_node;
 	struct workqueue_struct		*parallel_wq;
 	struct workqueue_struct		*serial_wq;
 	struct list_head		pslist;