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Date: Fri, 17 Feb 2017 20:11:36 +0300 From: Cyrill Gorcunov <gorcunov@...il.com> To: Andy Lutomirski <luto@...capital.net> Cc: Linux FS Devel <linux-fsdevel@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...uxfoundation.org>, Andrew Vagin <avagin@...tuozzo.com>, Pavel Emelyanov <xemul@...tuozzo.com>, Michael Kerrisk <mtk.manpages@...il.com>, Kirill Kolyshkin <kir@...nvz.org>, Andrey Vagin <avagin@...nvz.org> Subject: Re: [RFC 1/2] fs,eventpoll: Add ability to install target file by its number On Fri, Feb 17, 2017 at 08:52:59AM -0800, Andy Lutomirski wrote: > > > > To resolve this tie lets add EPOLL_CTL_DUP operation which simply takes > > target file descriptor number and installs it into a caller's file table, > > thus we can use kcmp() syscall and figure out which exactly file to be > > added into eventpoll on restore procedure. > > This is a scary thing to let an unprivileged process do. > > I'm wondering if there might be a nicer way to address this using a > better interface in /proc. Well, I tend to agree. Need to add security checking if the target file is accessable by a caller. As to better interface to procfs nothing comes to mind immediately. Another potential problem is that since it is never guaranteed that target file number listed in fdinfo matching existing /proc/pid/fd/N, so that I think we will have to use this dup functionality for every target file, which of course not that fast. Probably need to think more if I manage to invent some better and faster interface to find where exactly target file belong in the whole process tree of a container. Thanks for pointing about this security problem, Andy!
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