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Date:   Sun, 5 Jan 2020 14:30:07 +0100
From:   Christian Brauner <>
To:     Sargun Dhillon <>
Subject: Re: [PATCH v8 2/3] pid: Introduce pidfd_getfd syscall

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 

Acked-by: Christian Brauner <>

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