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
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 961fad1..f3a454c 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -358,6 +358,8 @@ static void tun_free_netdev(struct net_device *dev)
 {
        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, struct file *file, struct ifreq *ifr)
                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);

diff --git a/include/linux/net.h b/include/linux/net.h
index e9ac2df..dc95700 100644 (file)
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -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
 /**

diff --git a/net/socket.c b/net/socket.c
index 6e0ccc0..0452dca 100644 (file)
--- a/net/socket.c
+++ b/net/socket.c
@@ -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;
+
        this_cpu_sub(sockets_in_use, 1);
        if (!sock->file) {
                iput(SOCK_INODE(sock));