From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Brauner Subject: Re: [PATCH v8 2/3] pid: Introduce pidfd_getfd syscall Date: Sun, 5 Jan 2020 14:30:07 +0100 Message-ID: <20200105133005.ezt4y4d4oat55u6h@wittgenstein> References: <20200103162928.5271-1-sargun@sargun.me> <20200103162928.5271-3-sargun@sargun.me> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <20200103162928.5271-3-sargun@sargun.me> Sender: linux-kernel-owner@vger.kernel.org To: Sargun Dhillon Cc: linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, tycho@tycho.ws, jannh@google.com, cyphar@cyphar.com, oleg@redhat.com, luto@amacapital.net, viro@zeniv.linux.org.uk, gpascutto@mozilla.com, ealvarez@mozilla.com, fweimer@redhat.com, jld@mozilla.com, arnd@arndb.de List-Id: linux-api@vger.kernel.org On Fri, Jan 03, 2020 at 08:29:27AM -0800, Sargun Dhillon wrote: > This syscall allows for the retrieval of file descriptors from other > processes, based on their pidfd. This is possible using ptrace, and > injection of parasitic code to inject code which leverages SCM_RIGHTS > to move file descriptors between a tracee and a tracer. Unfortunately, > ptrace comes with a high cost of requiring the process to be stopped, > and breaks debuggers. This does not require stopping the process under > manipulation. > > One reason to use this is to allow sandboxers to take actions on file > descriptors on the behalf of another process. For example, this can be > combined with seccomp-bpf's user notification to do on-demand fd > extraction and take privileged actions. One such privileged action > is binding a socket to a privileged port. > > This also adds the syscall to all architectures at the same time. > > /* prototype */ > /* flags is currently reserved and should be set to 0 */ > int sys_pidfd_getfd(int pidfd, int fd, unsigned int flags); > > /* testing */ > Ran self-test suite on x86_64 > > Signed-off-by: Sargun Dhillon > Cc: Christian Brauner The prefered way of adding a syscall is to keep the implementation separate from the wiring up into the syscall tables. So please split the patch into two: - [2/4] pidfd_getfd() implementation - [3/4] pidfd_getfd() wiring up otherwise Acked-by: Christian Brauner