[PATCH 2/2] scsi: target: iscsi: fix use-after-free in iscsit_dec_session_usage_count()

[Maurizio Lombardi <mlombard@redhat.com>]

In iscsit_dec_session_usage_count(), the function calls complete() while
holding the sess->session_usage_lock. Similar to the connection usage
count logic, the waiter signaled by complete() (e.g., in the session
release path) may wake up and free the iscsit_session
structure immediately.

This creates a race condition where the current thread may attempt to
execute spin_unlock_bh() on a session structure that has already been
deallocated, resulting in a KASAN slab-use-after-free.

To resolve this, release the session_usage_lock before calling complete()
to ensure all dereferences of the sess pointer are finished before the
waiter is allowed to proceed with deallocation.

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reported-by: Zhaojuan Guo <zguo@redhat.com>
---
 drivers/target/iscsi/iscsi_target_util.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
index 3319394bf542..c1888c42afdd 100644
--- a/drivers/target/iscsi/iscsi_target_util.c
+++ b/drivers/target/iscsi/iscsi_target_util.c
@@ -741,8 +741,11 @@ void iscsit_dec_session_usage_count(struct iscsit_session *sess)
 	spin_lock_bh(&sess->session_usage_lock);
 	sess->session_usage_count--;
 
-	if (!sess->session_usage_count && sess->session_waiting_on_uc)
+	if (!sess->session_usage_count && sess->session_waiting_on_uc) {
+		spin_unlock_bh(&sess->session_usage_lock);
 		complete(&sess->session_waiting_on_uc_comp);
+		return;
+	}
 
 	spin_unlock_bh(&sess->session_usage_lock);
 }
-- 
2.47.3