Re: [RFC PATCH] ptrace: add PTRACE_GETFD request

On Fri, Dec 6, 2019 at 8:03 PM Sargun Dhillon [off-list ref] wrote:

On Fri, Dec 6, 2019 at 6:10 AM Tycho Andersen [off-list ref] wrote:

quoted

On Thu, Dec 05, 2019 at 11:44:53PM +0000, Sargun Dhillon wrote:

quoted

take action on an FD on behalf of the tracee. For example, this
can be combined with seccomp's user notification feature to extract
a file descriptor and call privileged syscalls, like binding
a socket to a privileged port.

This can already be accomplished via injecting parasite code like CRIU
does; adding a ptrace() command like this makes it much nicer to be
sure, but it is redundant.

How can you do this if the tracee doesn't have privilege? For example,
if the tracee doesn't have CAP_SYS_BIND_SERVICE, how could you
get it to bind to a port that's privileged without taking the file descriptor
and doing it in a process that does have CAP_SYS_BIND_SERVICE?

(You can let the parasite send the fd to the tracer via
SCM_CREDENTIALS if you have previously set up a unix domain socket for
this.)