smb: client: fix potential UAF in smb2_is_network_name_deleted()

Skip sessions that are being teared down (status == SES_EXITING) to
avoid UAF.

Cc: stable@vger.kernel.org
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Paulo Alcantara

fs/smb/client/smb2ops.c

@@ -2481,6 +2481,8 @@ smb2_is_network_name_deleted(char *buf, struct TCP_Server_Info *server)
 
 	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each_entry(ses, &pserver->smb_ses_list, smb_ses_list) {
+		if (cifs_ses_exiting(ses))
+			continue;
 		list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
 			if (tcon->tid == le32_to_cpu(shdr->Id.SyncId.TreeId)) {
 				spin_lock(&tcon->tc_lock);