From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Date: Thu, 23 Jul 2020 14:42:11 +0000 Subject: RE: [PATCH 03/26] bpfilter: reject kernel addresses Message-Id: List-Id: References: <20200723060908.50081-1-hch@lst.de> <20200723060908.50081-4-hch@lst.de> In-Reply-To: <20200723060908.50081-4-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: 'Christoph Hellwig' , "David S. Miller" , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Alexey Kuznetsov , Hideaki YOSHIFUJI , Eric Dumazet Cc: "linux-crypto@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "bpf@vger.kernel.org" , "netfilter-devel@vger.kernel.org" , "coreteam@netfilter.org" , "linux-sctp@vger.kernel.org" , "linux-hams@vger.kernel.org" , "linux-bluetooth@vger.kernel.org" , "bridge@lists.linux-foundation.org" , "linux-can@vger.kernel.org" , "dccp@vger.kernel.org" , "linux-decnet-user@lists.sourceforge.net" , "linux-wpan@vger.kernel.org" , "linux-s390@vger.kernel.org" , "mptcp@lists.01.org" , "lvs-devel@vger.kernel.org" , "rds-devel@oss.oracle.com" , "linux-afs@lists.infradead.org" , "tipc-discussion@lists.sourceforge.net" , "linux-x25@vger.kernel.org" From: Christoph Hellwig > Sent: 23 July 2020 07:09 > > The bpfilter user mode helper processes the optval address using > process_vm_readv. Don't send it kernel addresses fed under > set_fs(KERNEL_DS) as that won't work. What sort of operations is the bpf filter doing on the sockopt buffers? Any attempts to reject some requests can be thwarted by a second application thread modifying the buffer after the bpf filter has checked that it allowed. You can't do security by reading a user buffer twice. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)