netdev - RE: [PATCH] Crash in tun

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Date:	Mon, 23 Jul 2012 10:43:18 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Al Viro" <viro@...IV.linux.org.uk>,
	"David Miller" <davem@...emloft.net>
Cc:	<mikulas@...ax.karlin.mff.cuni.cz>, <eric.dumazet@...il.com>,
	<maxk@...lcomm.com>, <vtun@...ice.satix.net>,
	<netdev@...r.kernel.org>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	<linux-sctp@...r.kernel.org>
Subject: RE: [PATCH] Crash in tun

> 	BTW, speaking of struct file treatment related to sockets -
> there's this piece of code in iscsi:
>         /*
>          * The SCTP stack needs struct socket->file.
>          */
>         if ((np->np_network_transport == ISCSI_SCTP_TCP) ||
>             (np->np_network_transport == ISCSI_SCTP_UDP)) {
>                 if (!new_sock->file) {
>                         new_sock->file = kzalloc(
>                                         sizeof(struct file),
> GFP_KERNEL);
> 
> For one thing, as far as I can see it'not true - sctp does *not*
> depend on socket->file being non-NULL; it does, in one place,
> check socket->file->f_flags for O_NONBLOCK, but there it treats
> NULL socket->file as "flag no set".

The SCTP code certainly has unconditionally looked at file->f_flags,
we had to allocate a 'struct file' for our in-kernel socket code.
We set sock->file = NULL before the sock_release() call so
hopefully don't suffer the 'side effects'.

	David


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