[PATCH 6.1 41/69] scsi: target: iscsi: Fix use-after-free in iscsit_dec_session_usage_count()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Maurizio Lombardi <mlombard@redhat.com>

[ Upstream commit 84dc6037390b8607c5551047d3970336cb51ba9a ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 26dc8ed3045b6..61bcdc33f1230 100644
--- a/drivers/target/iscsi/iscsi_target_util.c
+++ b/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);
 }
-- 
2.51.0