path: root/net/core/sock.c
diff options
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/sock.c
parent6d446ec32f169c6a5d9bc90684a8082a6cbe90f6 (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/core/sock.c')
1 files changed, 2 insertions, 15 deletions
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;
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;
- 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;