[PATCH] scsi: iscsi: iscsi_tcp: Fix null-ptr-deref while calling getpeername()

[Li Jinlin <lijinlin3@xxxxxxxxxx>]

I got a kernel NULL pointer derference report as below:

    BUG: kernel NULL pointer dereference, address: 0000000000000038
    CPU: 4 PID: 1050 Comm: cat Not tainted 5.19.0 #38
    RIP: 0010:kernel_getpeername+0xf/0x30
    Call Trace:
     <TASK>
     ? iscsi_sw_tcp_conn_get_param+0x11f/0x17f
     show_conn_ep_param_ISCSI_PARAM_CONN_ADDRESS+0x90/0xb0
     dev_attr_show+0x1d/0x50
     sysfs_kf_seq_show+0xad/0x120
     kernfs_seq_show+0x2c/0x40
     seq_read_iter+0x12e/0x4d0
     ? aa_file_perm+0x177/0x590
     kernfs_fop_read_iter+0x183/0x210
     new_sync_read+0xfe/0x180
     ? 0xffffffff81000000
     vfs_read+0x14d/0x1a0
     ksys_read+0x6d/0xf0
     __x64_sys_read+0x1a/0x20
     do_syscall_64+0x3b/0x90
     entry_SYSCALL_64_after_hwframe+0x63/0xcd

The problem scenario is:

              CPU1                         CPU2
    -------------------------    ------------------------
    iscsi_sw_tcp_conn_get_param
      spin_lock_bh(&frwd_lock)
      if (!tcp_sw_conn || !tcp_sw_conn->sock)
         spin_unlock_bh(&frwd_lock)
         return -ENOTCONN

      sock = tcp_sw_conn->sock;
      sock_hold(sock->sk)
      spin_unlock_bh(&frwd_lock)
                                  iscsi_sw_tcp_release_conn
                                    spin_lock_bh(&frwd_lock)
                                    tcp_sw_conn->sock = NULL
                                    spin_unlock_bh(&frwd_lock)
                                    sockfd_put(sock)
                                      task_work
                                        __fput
                                          sock_close
                                            __sock_release
                                              sock->sk = NULL
                                              sock->ops = NULL
                                              sock->file = NULL
      kernel_getpeername
        sock->ops->getname
        ^^^^^^^^^
        NULL pointer dereference of sock->ops

sock_hold() and sock_put() can't ensure that sock_close() won't be
called before calling getpeername() or getsockname(). Using fget()
and sockfd_put() replace sock_hold() and sock_put(), and put them
under frwd_lock protection, to ensure that the socket struct is
preserved until after the getpeernaem() or getsockname() complete.

Fixes: bcf3a2953d36 ("scsi: iscsi: iscsi_tcp: Avoid holding spinlock while calling getpeername()")
Signed-off-by: Li Jinlin <lijinlin3@xxxxxxxxxx>
---
 drivers/scsi/iscsi_tcp.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
index 9fee70d6434a..63532dc3970d 100644
--- a/drivers/scsi/iscsi_tcp.c
+++ b/drivers/scsi/iscsi_tcp.c
@@ -612,8 +612,8 @@ static void iscsi_sw_tcp_release_conn(struct iscsi_conn *conn)
 
 	spin_lock_bh(&session->frwd_lock);
 	tcp_sw_conn->sock = NULL;
-	spin_unlock_bh(&session->frwd_lock);
 	sockfd_put(sock);
+	spin_unlock_bh(&session->frwd_lock);
 }
 
 static void iscsi_sw_tcp_conn_destroy(struct iscsi_cls_conn *cls_conn)
@@ -756,7 +756,7 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
 			return -ENOTCONN;
 		}
 		sock = tcp_sw_conn->sock;
-		sock_hold(sock->sk);
+		fget(sock->file);
 		spin_unlock_bh(&conn->session->frwd_lock);
 
 		if (param == ISCSI_PARAM_LOCAL_PORT)
@@ -765,7 +765,9 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
 		else
 			rc = kernel_getpeername(sock,
 						(struct sockaddr *)&addr);
-		sock_put(sock->sk);
+		spin_lock_bh(&conn->session->frwd_lock);
+		sockfd_put(sock);
+		spin_unlock_bh(&conn->session->frwd_lock);
 		if (rc < 0)
 			return rc;
 
@@ -808,12 +810,14 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
 			spin_unlock_bh(&session->frwd_lock);
 			return -ENOTCONN;
 		}
-		sock_hold(sock->sk);
+		fget(sock->file);
 		spin_unlock_bh(&session->frwd_lock);
 
 		rc = kernel_getsockname(sock,
 					(struct sockaddr *)&addr);
-		sock_put(sock->sk);
+		spin_lock_bh(&conn->session->frwd_lock);
+		sockfd_put(sock);
+		spin_unlock_bh(&conn->session->frwd_lock);
 		if (rc < 0)
 			return rc;
 
-- 
2.27.0