smb: client: fix potential UAF in cifs_stats_proc_show()

commit 0865ffe upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/smb/client/cifs_debug.c

@@ -736,6 +736,8 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 			}
 #endif /* STATS2 */
 		list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
+			if (cifs_ses_exiting(ses))
+				continue;
 			list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
 				i++;
 				seq_printf(m, "\n%d) %s", i, tcon->tree_name);