Re: [PATCH 1/2] fs: introduce sendfd() syscall

From: Eric Dumazet
Date: Tue Dec 02 2014 - 07:50:17 EST

On Tue, 2014-12-02 at 15:35 +1100, Alex Dubov wrote:
> Present patch introduces exceptionally easy to use, low latency and low
> overhead mechanism for transferring file descriptors between cooperating
> processes:
> int sendfd(pid_t pid, int sig, int fd)
> Given a target process pid, the sendfd() syscall will create a duplicate
> file descriptor in a target task's (referred by pid) file table pointing to
> the file references by descriptor fd. Then, it will attempt to notify the
> target task by issuing a Posix.1b real-time signal (sig), carrying the new
> file descriptor as integer payload. If real-time signal can not be enqueued
> at the destination signal queue, the newly created file descriptor will be
> promptly closed.
> Signed-off-by: Alex Dubov <oakad@xxxxxxxxx>
> ---

User A can send fd(s) to processes belonging to user B, even if user B
does (probably) not want this to happen ?

Also, relying on signals seems quite old fashion these days. How about
multi-threaded programs wanting separate channels to receive fds ?

Ability to flood fds and fill target file descriptors table looks very
dangerous to me. Some programs could break as they expect they control
fd allocations.

I like the idea of not having to use AF_UNIX and stick to a well defined
interface, but I do not like this asynchronous model.


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