From: Max Krasnyansky <maxk@qualcomm•com>
To: Mikulas Patocka <mikulas@artax•karlin.mff.cuni.cz>
Cc: Eric Dumazet <eric.dumazet@gmail•com>, <netdev@vger•kernel.org>,
<davem@davemloft•net>
Subject: Re: [PATCH] Crash in tun
Date: Thu, 19 Jul 2012 10:44:01 -0700 [thread overview]
Message-ID: <50084761.1030602@qualcomm.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1207191746170.7550@artax.karlin.mff.cuni.cz>
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 <mikulas@artax•karlin.mff.cuni.cz>
> 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));
>
next prev parent reply other threads:[~2012-07-19 17:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-19 1:12 [PATCH] Crash in tun Mikulas Patocka
2012-07-19 6:09 ` Eric Dumazet
2012-07-19 15:28 ` David Miller
2012-07-19 16:13 ` Mikulas Patocka
2012-07-19 17:44 ` Max Krasnyansky [this message]
2012-07-19 17:47 ` David Miller
2012-07-19 17:57 ` Max Krasnyansky
2012-07-20 18:23 ` David Miller
2012-07-21 7:55 ` Al Viro
2012-07-21 9:53 ` Nicholas A. Bellinger
2012-07-23 9:43 ` David Laight
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