linux-kernel - [PATCH/RFC] Handle EFAULT in partial recvmmsg was Re: [PATCH/RFC] Re: recvmmsg() timeout behavior strangeness [RESEND]

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: <20140529153342.GJ2764@kernel.org>
Date:	Thu, 29 May 2014 12:33:42 -0300
From:	'Arnaldo Carvalho de Melo' <acme@...nel.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Ondrej Bílka <neleai@...nam.cz>,
	Caitlin Bestler <caitlin.bestler@...il.com>,
	Neil Horman <nhorman@...driver.com>,
	Elie De Brauwer <eliedebrauwer@...il.com>,
	David Miller <davem@...emloft.net>,
	Steven Whitehouse <steve@...gwyn.com>,
	Rémi Denis-Courmont 
	<remi.denis-courmont@...ia.com>, Paul Moore <paul@...l-moore.com>,
	Chris Friesen <chris.friesen@...driver.com>
Subject: [PATCH/RFC] Handle EFAULT in partial recvmmsg was Re: [PATCH/RFC]
 Re: recvmmsg() timeout behavior strangeness [RESEND]

Em Thu, May 29, 2014 at 11:17:05AM -0300, 'Arnaldo Carvalho de Melo' escreveu:
> Em Thu, May 29, 2014 at 02:06:04PM +0000, David Laight escreveu:
> > From: 'Arnaldo Carvalho de Melo'
> > ...
> > > > I remember some discussions from an XNET standards meeting (I've forgotten
> > > > exactly which errors on which calls were being discussed).
> > > > My recollection is that you return success with a partial transfer
> > > > count for ANY error that happens after some data has been transferred.
> > > > The actual error will be returned when it happens again on the next
> > > > system call - Note the AGAIN, not a saved error.
 
> > > A saved error, for the right entity, in the recvmmsg case, that
> > > basically is batching multiple recvmsg syscalls, doesn't sound like a
> > > problem, i.e. the idea is to, as much as possible, mimic what multiple
> > > recvmsg calls would do, but reduce its in/out kernel (and inside kernel
> > > subsystems) overhead.
 
> > > Perhaps we can have something in between, i.e. for things like EFAULT,
> > > we should report straight away, effectively dropping whatever datagrams
> > > successfully received in the current batch, do you agree?
  
> > Not unreasonable - EFAULT shouldn't happen unless the application
> > is buggy.
 
> Ok.

So the patch below should handle it, and record that the packets were
dropped, not at the transport level, like UDP_MIB_INERRORS, for
instance, would indicate, but at the batching, recvmmsg level, so
perhaps we'll need a MIB variable for that.

Also a counterpart to the trace_kfree_skb(skb, udp_recvmsg) tracepoint
for dropwatch and similar tools to use, Neil?

I'm keeping this separate from the timeout update patch.

- Arnaldo

diff --git a/net/socket.c b/net/socket.c
index abf56b2a14f9..63491f015912 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2415,13 +2415,17 @@ out_put:
 		return datagrams;
 
 	if (datagrams != 0) {
+		if (err == -EFAULT) {
+			atomic_add(datagrams, &sock->sk->sk_drops);
+			return -EFAULT;
+		}
 		/*
 		 * We may return less entries than requested (vlen) if the
 		 * sock is non block and there aren't enough datagrams...
 		 */
 		if (err != -EAGAIN) {
 			/*
-			 * ... or  if recvmsg returns an error after we
+			 * ... or if recvmsg returns a socket error after we
 			 * received some datagrams, where we record the
 			 * error to return on the next call or if the
 			 * app asks about it using getsockopt(SO_ERROR).
--
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/