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From:   Ruihan Li <lrh2000@pku.edu.cn>
To:     linux-bluetooth@vger.kernel.org
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        Ruihan Li <lrh2000@pku.edu.cn>
Subject: [PATCH v2] Bluetooth: Fix potential double free caused by hci_conn_unlink
Date:   Mon,  1 May 2023 02:05:35 +0800
Message-Id: <20230430180535.168270-1-lrh2000@pku.edu.cn>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The hci_conn_unlink function is being called by hci_conn_del, which means
it should not call hci_conn_del with the input parameter conn again. If it
does, conn may have already been released when hci_conn_unlink returns,
leading to potential UAF and double-free issues.

This patch resolves the problem by modifying hci_conn_unlink to release
only conn's child links when necessary, but never release conn itself.

Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
---
Changes since v1:
 * CI complains that there are some merge conflicts. This is because
	void hci_conn_del(struct hci_conn *conn)
   this completely unrelated line makes the patch dependent on another fix:
	https://lore.kernel.org/linux-bluetooth/20230430171847.156825-1-lrh2000@pku.edu.cn/
   But actually, deleting that line makes the two patches independent of
   each other, and everything still works.

 net/bluetooth/hci_conn.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 85c34c837..5f388202f 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1083,8 +1083,18 @@ static void hci_conn_unlink(struct hci_conn *conn)
 	if (!conn->parent) {
 		struct hci_link *link, *t;
 
-		list_for_each_entry_safe(link, t, &conn->link_list, list)
-			hci_conn_unlink(link->conn);
+		list_for_each_entry_safe(link, t, &conn->link_list, list) {
+			struct hci_conn *child = link->conn;
+
+			hci_conn_unlink(child);
+
+			/* Due to race, SCO connection might be not established
+			 * yet at this point. Delete it now, otherwise it is
+			 * possible for it to be stuck and can't be deleted.
+			 */
+			if (child->handle == HCI_CONN_HANDLE_UNSET)
+				hci_conn_del(child);
+		}
 
 		return;
 	}
@@ -1100,12 +1110,5 @@ static void hci_conn_unlink(struct hci_conn *conn)
 
 	kfree(conn->link);
 	conn->link = NULL;
-
-	/* Due to race, SCO connection might be not established
-	 * yet at this point. Delete it now, otherwise it is
-	 * possible for it to be stuck and can't be deleted.
-	 */
-	if (conn->handle == HCI_CONN_HANDLE_UNSET)
-		hci_conn_del(conn);
 }
 
-- 
2.40.0