From mboxrd@z Thu Jan 1 00:00:00 1970 From: Max Krasnyansky Subject: Re: [PATCH] Crash in tun Date: Thu, 19 Jul 2012 10:44:01 -0700 Message-ID: <50084761.1030602@qualcomm.com> References: <1342678175.2626.3849.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , , To: Mikulas Patocka Return-path: Received: from wolverine01.qualcomm.com ([199.106.114.254]:2734 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752366Ab2GSRoH (ORCPT ); Thu, 19 Jul 2012 13:44:07 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 07/19/2012 09:13 AM, Mikulas Patocka wrote: > > > On Thu, 19 Jul 2012, Eric Dumazet wrote: > >> Hi Mikulas >> >> A fix for this problem is : http://patchwork.ozlabs.org/patch/170440/ > > If you call tun_free_netdev beacuse of a jump to an error label > err_free_sk, your patch still calls it with NULL file, causing a memory > corruption and a possible crash. > > Your patch doesn't fix sockets_in_use underflow. > > Maybe we can commit this patch --- it introduces a new flag > SOCK_EXTERNALLY_ALLOCATED to work around both problems. (it looks quite > nicer than my previous patch with file = (void *)1). I definitely like this second version better. Less hacky an all. btw I don't remember now who added the socket business to tun_struct and why. It seems to be messy in general. Originally version, back when I was still paying attention to it, didn't have sockets at all. Only char and net devices. It was much cleaner. Max > --- > > tun: fix a crash bug and a memory leak > > This patch fixes a crash > tun_chr_close -> netdev_run_todo -> tun_free_netdev -> sk_release_kernel -> > sock_release -> iput(SOCK_INODE(sock)) > introduced by commit 1ab5ecb90cb6a3df1476e052f76a6e8f6511cb3d > > The problem is that this socket is embedded in struct tun_struct, it has > no inode, iput is called on invalid inode, which modifies invalid memory > and optionally causes a crash. > > sock_release also decrements sockets_in_use, this causes a bug that > "sockets: used" field in /proc/*/net/sockstat keeps on decreasing when > creating and closing tun devices. > > This patch introduces a flag SOCK_EXTERNALLY_ALLOCATED that instructs > sock_release to not free the inode and not decrement sockets_in_use, > fixing both memory corruption and sockets_in_use underflow. > > It should be backported to 3.3 an 3.4 stabke. > > Signed-off-by: Mikulas Patocka > Cc: stable@kernel.org > > --- > drivers/net/tun.c | 3 +++ > include/linux/net.h | 1 + > net/socket.c | 3 +++ > 3 files changed, 7 insertions(+) > > Index: linux-3.4.5-fast/drivers/net/tun.c > =================================================================== > --- linux-3.4.5-fast.orig/drivers/net/tun.c 2012-07-19 17:55:16.000000000 +0200 > +++ linux-3.4.5-fast/drivers/net/tun.c 2012-07-19 17:58:30.000000000 +0200 > @@ -358,6 +358,8 @@ static void tun_free_netdev(struct net_d > { > struct tun_struct *tun = netdev_priv(dev); > > + BUG_ON(!test_bit(SOCK_EXTERNALLY_ALLOCATED, &tun->socket.flags)); > + > sk_release_kernel(tun->socket.sk); > } > > @@ -1115,6 +1117,7 @@ static int tun_set_iff(struct net *net, > tun->flags = flags; > tun->txflt.count = 0; > tun->vnet_hdr_sz = sizeof(struct virtio_net_hdr); > + set_bit(SOCK_EXTERNALLY_ALLOCATED, &tun->socket.flags); > > err = -ENOMEM; > sk = sk_alloc(&init_net, AF_UNSPEC, GFP_KERNEL, &tun_proto); > Index: linux-3.4.5-fast/include/linux/net.h > =================================================================== > --- linux-3.4.5-fast.orig/include/linux/net.h 2012-07-19 17:54:31.000000000 +0200 > +++ linux-3.4.5-fast/include/linux/net.h 2012-07-19 17:55:03.000000000 +0200 > @@ -72,6 +72,7 @@ struct net; > #define SOCK_NOSPACE 2 > #define SOCK_PASSCRED 3 > #define SOCK_PASSSEC 4 > +#define SOCK_EXTERNALLY_ALLOCATED 5 > > #ifndef ARCH_HAS_SOCKET_TYPES > /** > Index: linux-3.4.5-fast/net/socket.c > =================================================================== > --- linux-3.4.5-fast.orig/net/socket.c 2012-07-19 17:56:55.000000000 +0200 > +++ linux-3.4.5-fast/net/socket.c 2012-07-19 17:57:50.000000000 +0200 > @@ -522,6 +522,9 @@ void sock_release(struct socket *sock) > if (rcu_dereference_protected(sock->wq, 1)->fasync_list) > printk(KERN_ERR "sock_release: fasync list not empty!\n"); > > + if (test_bit(SOCK_EXTERNALLY_ALLOCATED, &sock->flags)) > + return; > + > percpu_sub(sockets_in_use, 1); > if (!sock->file) { > iput(SOCK_INODE(sock)); >