From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Subject: RE: [PATCH 32/33] sctp: add sctp_sock_get_primary_addr Date: Thu, 14 May 2020 12:30:17 +0000 Message-ID: References: <20200513062649.2100053-1-hch@lst.de> <20200513062649.2100053-33-hch@lst.de> <20200513180302.GC2491@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Return-path: Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:42484 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726388AbgENMaV (ORCPT ); Thu, 14 May 2020 08:30:21 -0400 In-Reply-To: Content-Language: en-US Sender: ceph-devel-owner@vger.kernel.org List-ID: To: 'Marcelo Ricardo Leitner' , 'Christoph Hellwig' Cc: "'David S. Miller'" , 'Jakub Kicinski' , 'Eric Dumazet' , 'Alexey Kuznetsov' , 'Hideaki YOSHIFUJI' , 'Vlad Yasevich' , 'Neil Horman' , 'Jon Maloy' , 'Ying Xue' , "'drbd-dev@lists.linbit.com'" , "'linux-block@vger.kernel.org'" , "'linux-kernel@vger.kernel.org'" , "'linux-rdma@vger.kernel.org'" , "'linux-nvme@lists.infradead.org'" , "'target-devel@vger.kernel.org'" From: David Laight > Sent: 14 May 2020 10:51 > From: Marcelo Ricardo Leitner > > Sent: 13 May 2020 19:03 > > > > On Wed, May 13, 2020 at 08:26:47AM +0200, Christoph Hellwig wrote: > > > Add a helper to directly get the SCTP_PRIMARY_ADDR sockopt from kernel > > > space without going through a fake uaccess. > > > > Same comment as on the other dlm/sctp patch. > > Wouldn't it be best to write sctp_[gs]etsockotp() that > use a kernel buffer and then implement the user-space > calls using a wrapper that does the copies to an on-stack > (or malloced if big) buffer. Actually looking at __sys_setsockopt() it calls BPF_CGROUP_RUN_PROG_SETSOCKOPT() which (by the look of it) can copy the user buffer into malloc()ed memory and cause set_fs(KERNEL_DS) be called. The only way to get rid of that set_fs() is to always have the buffer in kernel memory when the underlying setsockopt() code is called. The comment above __sys_[sg]etsockopt() about not knowing the length is just wrong. It probably applied to getsockopt() in the dim and distant past before it was made read-update. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)