libiscsi: fix potential buffer overrun in __iscsi_conn_send_pdu

libiscsi: fix potential buffer overrun in __iscsi_conn_send_pdu

commit db9bfd64b14a3a8f1868d2164518fdeab1b26ad1 upstream.

This patches fixes a potential buffer overrun in __iscsi_conn_send_pdu.
This function is used by iscsi drivers and userspace to send iscsi PDUs/
commands. For login commands, we have a set buffer size. For all other
commands we do not support data buffers.

This was reported by Dan Carpenter here:
http://www.spinics.net/lists/linux-scsi/msg66838.html

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>