linux-kernel - [PATCH 3.2 104/110] iscsi-target: Fix use-after-free during TPG session shutdown

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Message-ID: <lsq.1439201551.87764827@decadent.org.uk>
Date:	Mon, 10 Aug 2015 12:12:31 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Sunilkumar Nadumuttlu" <sjn@...era.io>,
	"Nicholas Bellinger" <nab@...ux-iscsi.org>
Subject: [PATCH 3.2 104/110] iscsi-target: Fix use-after-free during TPG
 session shutdown

3.2.71-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Nicholas Bellinger <nab@...ux-iscsi.org>

commit 417c20a9bdd1e876384127cf096d8ae8b559066c upstream.

This patch fixes a use-after-free bug in iscsit_release_sessions_for_tpg()
where se_portal_group->session_lock was incorrectly released/re-acquired
while walking the active se_portal_group->tpg_sess_list.

The can result in a NULL pointer dereference when iscsit_close_session()
shutdown happens in the normal path asynchronously to this code, causing
a bogus dereference of an already freed list entry to occur.

To address this bug, walk the session list checking for the same state
as before, but move entries to a local list to avoid dropping the lock
while walking the active list.

As before, signal using iscsi_session->session_restatement=1 for those
list entries to be released locally by iscsit_free_session() code.

Reported-by: Sunilkumar Nadumuttlu <sjn@...era.io>
Cc: Sunilkumar Nadumuttlu <sjn@...era.io>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/target/iscsi/iscsi_target.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -4509,6 +4509,7 @@ int iscsit_release_sessions_for_tpg(stru
 	struct iscsi_session *sess;
 	struct se_portal_group *se_tpg = &tpg->tpg_se_tpg;
 	struct se_session *se_sess, *se_sess_tmp;
+	LIST_HEAD(free_list);
 	int session_count = 0;
 
 	spin_lock_bh(&se_tpg->session_lock);
@@ -4530,14 +4531,17 @@ int iscsit_release_sessions_for_tpg(stru
 		}
 		atomic_set(&sess->session_reinstatement, 1);
 		spin_unlock(&sess->conn_lock);
-		spin_unlock_bh(&se_tpg->session_lock);
 
-		iscsit_free_session(sess);
-		spin_lock_bh(&se_tpg->session_lock);
+		list_move_tail(&se_sess->sess_list, &free_list);
+	}
+	spin_unlock_bh(&se_tpg->session_lock);
 
+	list_for_each_entry_safe(se_sess, se_sess_tmp, &free_list, sess_list) {
+		sess = (struct iscsi_session *)se_sess->fabric_sess_ptr;
+
+		iscsit_free_session(sess);
 		session_count++;
 	}
-	spin_unlock_bh(&se_tpg->session_lock);
 
 	pr_debug("Released %d iSCSI Session(s) from Target Portal"
 			" Group: %hu\n", session_count, tpg->tpgt);

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