cifs: fix panic in smb2_reconnect

mainline inclusion
from mainline-5.2-rc6
commit 0ff2b018b02f
category: bugfix
bugzilla: 16811
CVE: NA

https://gitee.com/src-openeuler/cifs-utils/issues/I1C1QY?from=project-issue
-------------------------------------------------

RH Bugzilla: 1702264

We need to protect so that the call to smb2_reconnect() in
smb2_reconnect_server() does not end up freeing the session
because it can lead to a use after free and crash.
Reviewed-by: NAurelien Aptel <aaptel@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NRonnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: NSteve French <stfrench@microsoft.com>
Reviewed-by: NPavel Shilovsky <pshilov@microsoft.com>
Conflicts:
  fs/cifs/cifsproto.h
  fs/cifs/connect.c
[yyl: make cifs_put_smb_ses() extern]
Reviewed-by: NZhang Xiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/cifs/cifsproto.h

@@ -526,6 +526,8 @@ extern int E_md4hash(const unsigned char *passwd, unsigned char *p16,
 extern int SMBencrypt(unsigned char *passwd, const unsigned char *c8,
 			unsigned char *p24);
 
+extern void cifs_put_smb_ses(struct cifs_ses *ses);
+
 void cifs_readdata_release(struct kref *refcount);
 int cifs_async_readv(struct cifs_readdata *rdata);
 int cifs_readv_receive(struct TCP_Server_Info *server, struct mid_q_entry *mid);

fs/cifs/connect.c

@@ -2732,8 +2732,7 @@ cifs_find_smb_ses(struct TCP_Server_Info *server, struct smb_vol *vol)
 	return NULL;
 }
 
-static void
-cifs_put_smb_ses(struct cifs_ses *ses)
+void cifs_put_smb_ses(struct cifs_ses *ses)
 {
 	unsigned int rc, xid;
 	struct TCP_Server_Info *server = ses->server;

fs/cifs/smb2pdu.c

@@ -2914,9 +2914,14 @@ void smb2_reconnect_server(struct work_struct *work)
 				tcon_exist = true;
 			}
 		}
+		/*
+		 * IPC has the same lifetime as its session and uses its
+		 * refcount.
+		 */
 		if (ses->tcon_ipc && ses->tcon_ipc->need_reconnect) {
 			list_add_tail(&ses->tcon_ipc->rlist, &tmp_list);
 			tcon_exist = true;
+			ses->ses_count++;
 		}
 	}
 	/*
@@ -2935,7 +2940,10 @@ void smb2_reconnect_server(struct work_struct *work)
 		else
 			resched = true;
 		list_del_init(&tcon->rlist);
-		cifs_put_tcon(tcon);
+		if (tcon->ipc)
+			cifs_put_smb_ses(tcon->ses);
+		else
+			cifs_put_tcon(tcon);
 	}
 
 	cifs_dbg(FYI, "Reconnecting tcons finished\n");