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

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>

diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
index 3319394bf542c48ce61fd00a70f24f28272b5955..c1888c42afdd5ec9b6a8b4aea55ec8336349bc2b 100644 (file)
--- 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);
 }