linux-kernel - Re: epoll and shared fd's

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 18 Jan 2008 13:10:18 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Pierre Habouzit <madcoder@...ian.org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: epoll and shared fd's

On Fri, 18 Jan 2008, Pierre Habouzit wrote:

>   Hi,
> 
>   I just came across a strange behavior of epoll that seems to
> contradict the documentation. Here is what happens:
> 
> * I have two processes P1 and P2, P1 accept()s connections, and send the
>   resulting file descriptors to P2 through a unix socket.
> 
> * P2 registers the received socket in his epollfd.
> 
>   [time passes]
> 
> * P2 is done with the socket and closes it
> 
> * P2 gets events for the socket again !
> 
> 
>   Though the documentation says that if a process closes a file
> descriptor, it gets unregistered. And yes I'm sure that P2 doens't dup()
> the file descriptor. Though (because of a bug) it was still open in
> P1[0], hence the referenced socket still live at the kernel level.
> 
>   Of course the userland workaround is to force the EPOLL_CTL_DEL before
> the close, which I now do, but costs me a syscall where I wanted to
> spare one :|

For epoll, a close is when the kernel file* is released (that is, when all 
its instances are gone).
We could put a special handling in filp_close(), but I don't think is a 
good idea, and we're better live with the current behaviour.



- Davide


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/