netdev - Re: question about BPF sk_skb_stream_verdict redirect and poll/epoll events

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: Sat, 23 Sep 2023 11:36:21 +0200
From: Ferenc Fejes <fejes@....elte.hu>
To: Farbod Shahinfar <farbod.shahinfar@...imi.it>, john.fastabend@...il.com,
  netdev@...r.kernel.org
Subject: Re: question about BPF sk_skb_stream_verdict redirect and
 poll/epoll events

Hi!

On Fri, 2023-09-22 at 19:32 +0200, Farbod Shahinfar wrote:
> Hello,
> 
> I am doing a simple experiment in which I send a message to a TCP
> server 
> and the server echoes the message. I am attaching a BPF sk_skb 
> stream_verdict program to the server socket to redirect the message
> back 
> to the client (redirects the SKB on the same socket but to the TX 
> queue). In my test, I noticed that the user-space server, which is
> using 
> the poll system call, is woken up, and when it reads the socket, 
> receives zero as the number of bytes read.

Do you poll for POLLIN events?

> 
> I first want to ask if this is the intended behavior.
> In case this is the intended behavior, my second question is, what 
> should I do to prevent the user program from waking up? I hope by not
> waking up the user program I could better use the available
> resources.

AFAIK sockets in sockmap are propagates every events to poll (fixme),
but with pollfd::events you can specify the ones makes sense to you
e.g.: POLLERR, POLLHUP, POLLRDHUP, etc.
> 
> Sincerely,
> Farbod

Ferenc