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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 /net/core/dev.c
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>
Diffstat (limited to 'net/core/dev.c')
-rw-r--r--net/core/dev.c34
1 files changed, 34 insertions, 0 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index fc1e289397f5..faebb398fb46 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