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br: fix use of ->rx_handler_data in code executed on non-rx_handler path
commit 859828c0ea476b42f3a93d69d117aaba90994b6f upstream. br_stp_rcv() is reached by non-rx_handler path. That means there is no guarantee that dev is bridge port and therefore simple NULL check of ->rx_handler_data is not enough. There is need to check if dev is really bridge port and since only rcu read lock is held here, do it by checking ->rx_handler pointer. Note that synchronize_net() in netdev_rx_handler_unregister() ensures this approach as valid. Introduced originally by: commitf350a0a873
"bridge: use rx_handler_data pointer to store net_bridge_port pointer" Fixed but not in the best way by: commitb5ed54e94d
"bridge: fix RCU races with bridge port" Reintroduced by: commit 716ec052d2280d511e10e90ad54a86f5b5d4dcc2 "bridge: fix NULL pointer deref of br_port_get_rcu" Please apply to stable trees as well. Thanks. RH bugzilla reference: https://bugzilla.redhat.com/show_bug.cgi?id=1025770 Reported-by: Laine Stump <laine@redhat.com> Debugged-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Jiri Pirko <jiri@resnulli.us> Acked-by: Michael S. Tsirkin <mst@redhat.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Cc: Andrew Collins <bsderandrew@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -429,6 +429,16 @@ extern netdev_features_t br_features_recompute(struct net_bridge *br,
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extern int br_handle_frame_finish(struct sk_buff *skb);
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extern rx_handler_result_t br_handle_frame(struct sk_buff **pskb);
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static inline bool br_rx_handler_check_rcu(const struct net_device *dev)
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{
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return rcu_dereference(dev->rx_handler) == br_handle_frame;
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}
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static inline struct net_bridge_port *br_port_get_check_rcu(const struct net_device *dev)
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{
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return br_rx_handler_check_rcu(dev) ? br_port_get_rcu(dev) : NULL;
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}
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/* br_ioctl.c */
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extern int br_dev_ioctl(struct net_device *dev, struct ifreq *rq, int cmd);
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extern int br_ioctl_deviceless_stub(struct net *net, unsigned int cmd, void __user *arg);
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@ -153,7 +153,7 @@ void br_stp_rcv(const struct stp_proto *proto, struct sk_buff *skb,
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if (buf[0] != 0 || buf[1] != 0 || buf[2] != 0)
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goto err;
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p = br_port_get_rcu(dev);
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p = br_port_get_check_rcu(dev);
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if (!p)
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goto err;
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