Sat, Dec 07, 2013 at 08:10:45PM CET, vyasevich@xxxxxxxxx wrote: >On 12/07/2013 03:51 AM, Jiri Pirko wrote: >> Fri, Dec 06, 2013 at 10:10:28PM CET, stephen@xxxxxxxxxxxxxxxxxx wrote: >>> On Fri, 06 Dec 2013 15:43:21 -0500 (EST) >>> David Miller <davem@xxxxxxxxxxxxx> wrote: >>> >>>> From: Jiri Pirko <jiri@xxxxxxxxxxx> >>>> Date: Thu, 5 Dec 2013 16:27:37 +0100 >>>> >>>>> 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: >>>>> commit f350a0a87374418635689471606454abc7beaa3a >>>>> "bridge: use rx_handler_data pointer to store net_bridge_port pointer" >>>>> >>>>> Fixed but not in the best way by: >>>>> commit b5ed54e94d324f17c97852296d61a143f01b227a >>>>> "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@xxxxxxxxxx> >>>>> Debugged-by: Michael S. Tsirkin <mst@xxxxxxxxxx> >>>>> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> >>>>> Signed-off-by: Jiri Pirko <jiri@xxxxxxxxxxx> >>>>> --- >>>>> v1->v2: moved br_port_get_check_rcu definition below br_handle_frame definition >>>> >>>> Applied and queued up for -stable, thanks Jiri. >>> >>> How come you ignored my simpler fix, that used the existing logic. >>> I don't like introducing this especially into the stable; much prefer >>> to go back to testing the flag as was being done before. >> >> Although your patch is technically sane, it depends on rtnl indirectly. > >Pardon my ignorance, but I've been staring at this and I can't for >the life of me see the dependency. > >The IFF_BRIDGE_PORT flag is set after the rx_handler is registered, >so we are safe there. The rcu primitives will guarantee that the flag >will be set by the time rx_handler and rx_handler_data are set. > >The flag is cleared before rx_handler is unregistered, so it is >still valid to check for it in stp code. Once the flag is cleared >we may still have a valid rx_handler during the rcu grace period, but >will still avoid doing processing. > >So, where is the dependency on the rtnl? Imagine br would release the netdev and some other rx_handler user would enslave the same netdev. This two events would happen between IFF_BRIDGE_PORT flag check and rx_handler_data get. That is what rtnl_lock prevents from happening. > >Thanks >-vlad > >> My patch depends on rcu locking and synchronize_rcu which is direct. >> Therefore I think it is more appropriate. >> >> Jiri >> >> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe netdev" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >
