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authorNicolas Schichan <nschichan@freebox.fr>2013-06-26 17:23:42 +0200
committerDavid S. Miller <davem@davemloft.net>2013-06-26 13:42:54 -0700
commit5dbe7c178d3f0a4634f088d9e729f1909b9ddcd1 (patch)
tree8945b6c5125b57cee5f36e903fc995e58664a639
parent6d446ec32f169c6a5d9bc90684a8082a6cbe90f6 (diff)
downloadlinux-linaro-stable-5dbe7c178d3f0a4634f088d9e729f1909b9ddcd1.tar.gz
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: Nicolas Schichan <nschichan@freebox.fr> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/linux/netdevice.h1
-rw-r--r--net/core/dev.c34
-rw-r--r--net/core/dev_ioctl.c19
-rw-r--r--net/core/sock.c17
4 files changed, 41 insertions, 30 deletions
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 60584b1..96e4c21 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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);
diff --git a/net/core/dev.c b/net/core/dev.c
index fc1e289..faebb39 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -792,6 +792,40 @@ 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
* @type: media type of device
diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index 6cc0481..5b7d0e1 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -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;
diff --git a/net/core/sock.c b/net/core/sock.c
index 88868a9..d6d024c 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -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;