linux-kernel - Re: [PATCH v3 0/4] Add pidfd getfd ioctl (Was Add ptrace get

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Date:   Tue, 17 Dec 2019 04:02:29 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Sargun Dhillon <sargun@...gun.me>
Cc:     linux-kernel@...r.kernel.org,
        containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tycho@...ho.ws, jannh@...gle.com,
        cyphar@...har.com, oleg@...hat.com, luto@...capital.net,
        viro@...iv.linux.org.uk, gpascutto@...illa.com,
        ealvarez@...illa.com, fweimer@...hat.com, jld@...illa.com
Subject: Re: [PATCH v3 0/4] Add pidfd getfd ioctl (Was Add ptrace get_fd
 request)

On Tue, Dec 17, 2019 at 12:58:45AM +0000, Sargun Dhillon wrote:
> This patchset introduces a mechanism to capture file descriptors from other
> processes by pidfd and ioctl. Although this can be achieved using

I like the idea in general as it's quite useful in general. And also for
the seccomp notifier and probably for CRIU too.
A few things that crossed my mind.
A thing I'm worried about is that this will be a stepping stone for
people argue for an fd-replacement feature though I think that
fd-injection not replacement might be sufficient.

I wonder whether we need to worry about special file descriptors, i.e.
anything anon-inode based, or devpts devices but I guess those concerns
already apply to ptrace anyway.

One more thing, with GETFD it seems useful to me that later we can add
a new flag - like I suggested in the previous version - to the seccomp
notifier that would allow a caller to request that with each seccomp
message received via the notifier ioctl() from the kernel a pidfd is
sent along. This would make it quite elegant to get fds for the
supervised task.

Christian