Bluetooth: Fix UAF in hci_conn_hash_flush again

Commit 06149746e720 ("Bluetooth: hci_conn: Add support for linking
multiple hcon") reintroduced a previously fixed bug [1] ("KASAN:
slab-use-after-free Read in hci_conn_hash_flush"). This bug was
originally fixed by commit 5dc7d23e167e ("Bluetooth: hci_conn: Fix
possible UAF").

The hci_conn_unlink function was added to avoid invalidating the link
traversal caused by successive hci_conn_del operations releasing extra
connections. However, currently hci_conn_unlink itself also releases
extra connections, resulted in the reintroduced bug.

This patch follows a more robust solution for cleaning up all
connections, by repeatedly removing the first connection until there are
none left. This approach does not rely on the inner workings of
hci_conn_del and ensures proper cleanup of all connections.

Meanwhile, we need to make sure that hci_conn_del never fails. Indeed it
doesn't, as it now always returns zero. To make this a bit clearer, this
patch also changes its return type to void.

Reported-by: syzbot+8bb72f86fc823817bc5d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-bluetooth/000000000000aa920505f60d25ad@google.com/
Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
Co-developed-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index a6c8aee..8baf346 100644 (file)
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -1327,7 +1327,7 @@ int hci_le_create_cis(struct hci_conn *conn);
 
 struct hci_conn *hci_conn_add(struct hci_dev *hdev, int type, bdaddr_t *dst,
                              u8 role);
-int hci_conn_del(struct hci_conn *conn);
+void hci_conn_del(struct hci_conn *conn);
 void hci_conn_hash_flush(struct hci_dev *hdev);
 void hci_conn_check_pending(struct hci_dev *hdev);
 

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 44d0643..ce58835 100644 (file)
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1088,6 +1088,14 @@ static void hci_conn_unlink(struct hci_conn *conn)
 
                        hci_conn_unlink(child);
 
+                       /* If hdev is down it means
+                        * hci_dev_close_sync/hci_conn_hash_flush is in progress
+                        * and links don't need to be cleanup as all connections
+                        * would be cleanup.
+                        */
+                       if (!test_bit(HCI_UP, &hdev->flags))
+                               continue;
+
                        /* 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.
@@ -1112,7 +1120,7 @@ static void hci_conn_unlink(struct hci_conn *conn)
        conn->link = NULL;
 }
 
-int hci_conn_del(struct hci_conn *conn)
+void hci_conn_del(struct hci_conn *conn)
 {
        struct hci_dev *hdev = conn->hdev;
 
@@ -1163,8 +1171,6 @@ int hci_conn_del(struct hci_conn *conn)
         * rest of hci_conn_del.
         */
        hci_conn_cleanup(conn);
-
-       return 0;
 }
 
 struct hci_dev *hci_get_route(bdaddr_t *dst, bdaddr_t *src, uint8_t src_type)
@@ -2465,22 +2471,27 @@ timer:
 /* Drop all connection on the device */
 void hci_conn_hash_flush(struct hci_dev *hdev)
 {
-       struct hci_conn_hash *h = &hdev->conn_hash;
-       struct hci_conn *c, *n;
+       struct list_head *head = &hdev->conn_hash.list;
+       struct hci_conn *conn;
 
        BT_DBG("hdev %s", hdev->name);
 
-       list_for_each_entry_safe(c, n, &h->list, list) {
-               c->state = BT_CLOSED;
-
-               hci_disconn_cfm(c, HCI_ERROR_LOCAL_HOST_TERM);
+       /* We should not traverse the list here, because hci_conn_del
+        * can remove extra links, which may cause the list traversal
+        * to hit items that have already been released.
+        */
+       while ((conn = list_first_entry_or_null(head,
+                                               struct hci_conn,
+                                               list)) != NULL) {
+               conn->state = BT_CLOSED;
+               hci_disconn_cfm(conn, HCI_ERROR_LOCAL_HOST_TERM);
 
                /* Unlink before deleting otherwise it is possible that
                 * hci_conn_del removes the link which may cause the list to
                 * contain items already freed.
                 */
-               hci_conn_unlink(c);
-               hci_conn_del(c);
+               hci_conn_unlink(conn);
+               hci_conn_del(conn);
        }
 }