scsi: iscsi: iscsi_tcp: Avoid holding spinlock while calling getpeername()

The kernel may fail to boot or devices may fail to come up when
initializing iscsi_tcp devices starting with Linux 5.8.

Commit a79af8a6 ("[SCSI] iscsi_tcp: use iscsi_conn_get_addr_param
libiscsi function") introduced getpeername() within the session spinlock.

Commit 1b66d253 ("bpf: Add get{peer, sock}name attach types for
sock_addr") introduced BPF_CGROUP_RUN_SA_PROG_LOCK() within getpeername(),
which acquires a mutex and when used from iscsi_tcp devices can now lead to
"BUG: scheduling while atomic:" and subsequent damage.

Ensure that the spinlock is released before calling getpeername() or
getsockname(). sock_hold() and sock_put() are used to ensure that the
socket reference is preserved until after the getpeername() or
getsockname() complete.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1877345
Link: https://lkml.org/lkml/2020/7/28/1085
Link: https://lkml.org/lkml/2020/8/31/459
Link: https://lore.kernel.org/r/20200928043329.606781-1-mark.mielke@gmail.com
Fixes: a79af8a6 ("[SCSI] iscsi_tcp: use iscsi_conn_get_addr_param libiscsi function")
Fixes: 1b66d253 ("bpf: Add get{peer, sock}name attach types for sock_addr")
Cc: stable@vger.kernel.org
Reported-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Mark Mielke <mark.mielke@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/iscsi_tcp.c

@@ -736,6 +736,7 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
 	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
 	struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
 	struct sockaddr_in6 addr;
+	struct socket *sock;
 	int rc;
 
 	switch(param) {
@@ -747,13 +748,17 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
 			spin_unlock_bh(&conn->session->frwd_lock);
 			return -ENOTCONN;
 		}
+		sock = tcp_sw_conn->sock;
+		sock_hold(sock->sk);
+		spin_unlock_bh(&conn->session->frwd_lock);
+
 		if (param == ISCSI_PARAM_LOCAL_PORT)
-			rc = kernel_getsockname(tcp_sw_conn->sock,
+			rc = kernel_getsockname(sock,
 						(struct sockaddr *)&addr);
 		else
-			rc = kernel_getpeername(tcp_sw_conn->sock,
+			rc = kernel_getpeername(sock,
 						(struct sockaddr *)&addr);
-		spin_unlock_bh(&conn->session->frwd_lock);
+		sock_put(sock->sk);
 		if (rc < 0)
 			return rc;
 
@@ -775,6 +780,7 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
 	struct iscsi_tcp_conn *tcp_conn;
 	struct iscsi_sw_tcp_conn *tcp_sw_conn;
 	struct sockaddr_in6 addr;
+	struct socket *sock;
 	int rc;
 
 	switch (param) {
@@ -789,16 +795,18 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
 			return -ENOTCONN;
 		}
 		tcp_conn = conn->dd_data;
-
 		tcp_sw_conn = tcp_conn->dd_data;
-		if (!tcp_sw_conn->sock) {
+		sock = tcp_sw_conn->sock;
+		if (!sock) {
 			spin_unlock_bh(&session->frwd_lock);
 			return -ENOTCONN;
 		}
+		sock_hold(sock->sk);
+		spin_unlock_bh(&session->frwd_lock);
 
-		rc = kernel_getsockname(tcp_sw_conn->sock,
+		rc = kernel_getsockname(sock,
 					(struct sockaddr *)&addr);
-		spin_unlock_bh(&session->frwd_lock);
+		sock_put(sock->sk);
 		if (rc < 0)
 			return rc;