netdev - Re: [PATCH] Generalize socket rx gap / receive queue overflow cmsg

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]

Message-ID: <20091008135435.GA23928@hmsreliant.think-freely.org>
Date:	Thu, 8 Oct 2009 09:54:35 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, socketcan@...tkopp.net
Subject: Re: [PATCH] Generalize socket rx gap / receive queue overflow cmsg

> 
> > +	if (check_drops) {
> > +		skb = skb_recv_datagram(sk, flags|MSG_PEEK,
> > +				flags & MSG_DONTWAIT, &err);
> 
> 	Ouch, this is too expensive, please find another way :)
> 
> > +		if (skb) {
> > +			gap = skb->dropcount;
> > +			consume_skb(skb);
> > +		}
> > +	}
> > +
I'm not sure that I see the expense here, and what expense there is, I don't see
how it avoidable.  In order to do this reporting at the socket level, we need to
look at the skb at the head of the receive queue.  But we need to do so in a way
thats consistent with the flags being passed in (i.e. if this is a blocking
socket, we need to block here until something is available to read).  Then its
just an atomic_inc on skb->users, followed by a dec in the consume_skb.  I could
implement the logic for DONTWAIT myself, and skip the atomic_inc/dec, but I'm
not sure thats much of a savings.  If you have another thought, I'm certainly
open to it.

Neil

> > +	rc = sock->ops->recvmsg(iocb, sock, msg, size, flags);
> > +
> > +	if (check_drops && (rc > 0))
> 
> 		&& gap != 0
> 
> > +		put_cmsg(msg, SOL_SOCKET, SO_RXQ_OVFL, sizeof(__u32), &gap);
> > +
> 
> 
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html