Commit 5dbe7c17 authored by Nicolas Schichan's avatar Nicolas Schichan Committed by David S. Miller

net: fix kernel deadlock with interface rename and netdev name retrieval.

When the kernel (compiled with CONFIG_PREEMPT=n) is performing the
rename of a network interface, it can end up waiting for a workqueue
to complete. If userland is able to invoke a SIOCGIFNAME ioctl or a
SO_BINDTODEVICE getsockopt in between, the kernel will deadlock due to
the fact that read_secklock_begin() will spin forever waiting for the
writer process (the one doing the interface rename) to update the
devnet_rename_seq sequence.

This patch fixes the problem by adding a helper (netdev_get_name())
and using it in the code handling the SIOCGIFNAME ioctl and
SO_BINDTODEVICE setsockopt.

The netdev_get_name() helper uses raw_seqcount_begin() to avoid
spinning forever, waiting for devnet_rename_seq->sequence to become
even. cond_resched() is used in the contended case, before retrying
the access to give the writer process a chance to finish.

The use of raw_seqcount_begin() will incur some unneeded work in the
reader process in the contended case, but this is better than
deadlocking the system.
Signed-off-by: default avatarNicolas Schichan <nschichan@freebox.fr>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 6d446ec3
......@@ -1695,6 +1695,7 @@ extern int init_dummy_netdev(struct net_device *dev);
extern struct net_device *dev_get_by_index(struct net *net, int ifindex);
extern struct net_device *__dev_get_by_index(struct net *net, int ifindex);
extern struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex);
extern int netdev_get_name(struct net *net, char *name, int ifindex);
extern int dev_restart(struct net_device *dev);
#ifdef CONFIG_NETPOLL_TRAP
extern int netpoll_trap(void);
......
......@@ -791,6 +791,40 @@ struct net_device *dev_get_by_index(struct net *net, int ifindex)
}
EXPORT_SYMBOL(dev_get_by_index);
/**
* netdev_get_name - get a netdevice name, knowing its ifindex.
* @net: network namespace
* @name: a pointer to the buffer where the name will be stored.
* @ifindex: the ifindex of the interface to get the name from.
*
* The use of raw_seqcount_begin() and cond_resched() before
* retrying is required as we want to give the writers a chance
* to complete when CONFIG_PREEMPT is not set.
*/
int netdev_get_name(struct net *net, char *name, int ifindex)
{
struct net_device *dev;
unsigned int seq;
retry:
seq = raw_seqcount_begin(&devnet_rename_seq);
rcu_read_lock();
dev = dev_get_by_index_rcu(net, ifindex);
if (!dev) {
rcu_read_unlock();
return -ENODEV;
}
strcpy(name, dev->name);
rcu_read_unlock();
if (read_seqcount_retry(&devnet_rename_seq, seq)) {
cond_resched();
goto retry;
}
return 0;
}
/**
* dev_getbyhwaddr_rcu - find a device by its hardware address
* @net: the applicable net namespace
......
......@@ -19,9 +19,8 @@
static int dev_ifname(struct net *net, struct ifreq __user *arg)
{
struct net_device *dev;
struct ifreq ifr;
unsigned seq;
int error;
/*
* Fetch the caller's info block.
......@@ -30,19 +29,9 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg)
if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))
return -EFAULT;
retry:
seq = read_seqcount_begin(&devnet_rename_seq);
rcu_read_lock();
dev = dev_get_by_index_rcu(net, ifr.ifr_ifindex);
if (!dev) {
rcu_read_unlock();
return -ENODEV;
}
strcpy(ifr.ifr_name, dev->name);
rcu_read_unlock();
if (read_seqcount_retry(&devnet_rename_seq, seq))
goto retry;
error = netdev_get_name(net, ifr.ifr_name, ifr.ifr_ifindex);
if (error)
return error;
if (copy_to_user(arg, &ifr, sizeof(struct ifreq)))
return -EFAULT;
......
......@@ -571,9 +571,7 @@ static int sock_getbindtodevice(struct sock *sk, char __user *optval,
int ret = -ENOPROTOOPT;
#ifdef CONFIG_NETDEVICES
struct net *net = sock_net(sk);
struct net_device *dev;
char devname[IFNAMSIZ];
unsigned seq;
if (sk->sk_bound_dev_if == 0) {
len = 0;
......@@ -584,20 +582,9 @@ static int sock_getbindtodevice(struct sock *sk, char __user *optval,
if (len < IFNAMSIZ)
goto out;
retry:
seq = read_seqcount_begin(&devnet_rename_seq);
rcu_read_lock();
dev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if);
ret = -ENODEV;
if (!dev) {
rcu_read_unlock();
ret = netdev_get_name(net, devname, sk->sk_bound_dev_if);
if (ret)
goto out;
}
strcpy(devname, dev->name);
rcu_read_unlock();
if (read_seqcount_retry(&devnet_rename_seq, seq))
goto retry;
len = strlen(devname) + 1;
......
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