Re: [PATCH] Crash in tun
From: Max Krasnyansky <hidden>
Date: 2012-07-19 17:44:07
On 07/19/2012 09:13 AM, Mikulas Patocka wrote:
On Thu, 19 Jul 2012, Eric Dumazet wrote:quoted
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
quoted hunk ↗ jump to hunk
--- 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));