diff options
author | Nicolas Schichan <nschichan@freebox.fr> | 2013-06-26 17:23:42 +0200 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2013-06-26 13:42:54 -0700 |
commit | 5dbe7c178d3f0a4634f088d9e729f1909b9ddcd1 (patch) | |
tree | 8945b6c5125b57cee5f36e903fc995e58664a639 /net | |
parent | 6d446ec32f169c6a5d9bc90684a8082a6cbe90f6 (diff) |
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>
Diffstat (limited to 'net')
-rw-r--r-- | net/core/dev.c | 34 | ||||
-rw-r--r-- | net/core/dev_ioctl.c | 19 | ||||
-rw-r--r-- | net/core/sock.c | 17 |
3 files changed, 40 insertions, 30 deletions
diff --git a/net/core/dev.c b/net/core/dev.c index fc1e289397f..faebb398fb4 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 6cc0481faad..5b7d0e1d066 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 88868a9d21d..d6d024cfaaa 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; |