scsi: target: iscsi: Fix use-after-free in iscsit_dec_session_usage_count()

jira VULN-176313
cve CVE-2026-23193
commit-author Maurizio Lombardi <mlombard@redhat.com>
commit 84dc603

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>
	Reviewed-by: Mike Christie <michael.christie@oracle.com>
Link: https://patch.msgid.link/20260112165352.138606-3-mlombard@redhat.com
	Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from commit 84dc603)
	Signed-off-by: Roxana Nicolescu <rnicolescu@ciq.com>

Author: roxanan1996

drivers/target/iscsi/iscsi_target_util.c

@@ -785,8 +785,11 @@ 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);
 }