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Subject[PATCH-v2 4/4] target: Obtain se_node_acl->acl_kref during get_initiator_node_acl
Date
From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch addresses a long standing race where obtaining
se_node_acl->acl_kref in __transport_register_session()
happens a bit too late, and leaves open the potential
for core_tpg_del_initiator_node_acl() to hit a NULL
pointer dereference.

Instead, take ->acl_kref in core_tpg_get_initiator_node_acl()
while se_portal_group->acl_node_mutex is held, and move the
final target_put_nacl() from transport_deregister_session()
into transport_free_session() so that fabric driver login
failure handling using the modern method to still work
as expected.

Also, update core_tpg_check_initiator_node_acl() to take
an extra reference for dynamically generated acls for
demo-mode, before returning to fabric caller.

Note the existing wait_for_completion(&acl->acl_free_comp)
in core_tpg_del_initiator_node_acl() does not change.

Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
---
drivers/target/target_core_tpg.c | 18 +++++++++++++++++-
drivers/target/target_core_transport.c | 18 ++++++++++++------
2 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 66a2c6f..5221aee 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -75,9 +75,16 @@ struct se_node_acl *core_tpg_get_initiator_node_acl(
unsigned char *initiatorname)
{
struct se_node_acl *acl;
-
+ /*
+ * Obtain the acl_kref now, which will be dropped upon the
+ * release of se_sess memory within transport_free_session().
+ */
mutex_lock(&tpg->acl_node_mutex);
acl = __core_tpg_get_initiator_node_acl(tpg, initiatorname);
+ if (acl) {
+ if (!kref_get_unless_zero(&acl->acl_kref))
+ acl = NULL;
+ }
mutex_unlock(&tpg->acl_node_mutex);

return acl;
@@ -240,6 +247,15 @@ struct se_node_acl *core_tpg_check_initiator_node_acl(
acl = target_alloc_node_acl(tpg, initiatorname);
if (!acl)
return NULL;
+ /*
+ * When allocating a dynamically generated node_acl, go ahead
+ * and take the extra kref now before returning to the fabric
+ * driver caller.
+ *
+ * Note this reference will be released at session shutdown
+ * time within transport_free_session() code.
+ */
+ kref_get(&acl->acl_kref);
acl->dynamic_node_acl = 1;

/*
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 7b05ebf..c5035b9 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -341,7 +341,6 @@ void __transport_register_session(
&buf[0], PR_REG_ISID_LEN);
se_sess->sess_bin_isid = get_unaligned_be64(&buf[0]);
}
- kref_get(&se_nacl->acl_kref);

spin_lock_irq(&se_nacl->nacl_sess_lock);
/*
@@ -464,6 +463,15 @@ EXPORT_SYMBOL(transport_deregister_session_configfs);

void transport_free_session(struct se_session *se_sess)
{
+ struct se_node_acl *se_nacl = se_sess->se_node_acl;
+ /*
+ * Drop the se_node_acl->nacl_kref obtained from within
+ * core_tpg_get_initiator_node_acl().
+ */
+ if (se_nacl) {
+ se_sess->se_node_acl = NULL;
+ target_put_nacl(se_nacl);
+ }
if (se_sess->sess_cmd_map) {
percpu_ida_destroy(&se_sess->sess_tag_pool);
kvfree(se_sess->sess_cmd_map);
@@ -478,7 +486,7 @@ void transport_deregister_session(struct se_session *se_sess)
const struct target_core_fabric_ops *se_tfo;
struct se_node_acl *se_nacl;
unsigned long flags;
- bool comp_nacl = true, drop_nacl = false;
+ bool drop_nacl = false;

if (!se_tpg) {
transport_free_session(se_sess);
@@ -510,18 +518,16 @@ void transport_deregister_session(struct se_session *se_sess)
if (drop_nacl) {
core_tpg_wait_for_nacl_pr_ref(se_nacl);
core_free_device_list_for_node(se_nacl, se_tpg);
+ se_sess->se_node_acl = NULL;
kfree(se_nacl);
- comp_nacl = false;
}
pr_debug("TARGET_CORE[%s]: Deregistered fabric_sess\n",
se_tpg->se_tpg_tfo->get_fabric_name());
/*
* If last kref is dropping now for an explicit NodeACL, awake sleeping
* ->acl_free_comp caller to wakeup configfs se_node_acl->acl_group
- * removal context.
+ * removal context from within transport_free_session() code.
*/
- if (se_nacl && comp_nacl)
- target_put_nacl(se_nacl);

transport_free_session(se_sess);
}
--
1.9.1
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