Re: [PATCH] NETLABEL: Fix an RCU warning

[Eric Dumazet <eric.dumazet@gmail.com>]

Le jeudi 25 mars 2010 à 11:06 +0000, David Howells a écrit :
> Fix an RCU warning in the netlabel code due to missing rcu read locking around
> an rcu_dereference() in netlbl_unlhsh_hash() when called from
> netlbl_unlhsh_netdev_handler():
> 
> ===================================================
> [ INFO: suspicious rcu_dereference_check() usage. ]
> ---------------------------------------------------
> net/netlabel/netlabel_unlabeled.c:246 invoked rcu_dereference_check() without protection!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 1, debug_locks = 0
> 2 locks held by ip/5108:
>  #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff812c4a36>] rtnl_lock+0x12/0x14
>  #1:  (netlbl_unlhsh_lock){+.+...}, at: [<ffffffff8134daa4>] netlbl_unlhsh_netdev_handler+0x1e/0x86
> 
> stack backtrace:
> Pid: 5108, comm: ip Not tainted 2.6.34-rc2-cachefs #114
> Call Trace:
>  [<ffffffff8105121f>] lockdep_rcu_dereference+0xaa/0xb2
>  [<ffffffff8134d781>] netlbl_unlhsh_hash+0x3e/0x50
>  [<ffffffff8134d7a1>] netlbl_unlhsh_search_iface+0xe/0x84
>  [<ffffffff8134daaf>] netlbl_unlhsh_netdev_handler+0x29/0x86
>  [<ffffffff81048362>] notifier_call_chain+0x32/0x5e
>  [<ffffffff810483fe>] raw_notifier_call_chain+0xf/0x11
>  [<ffffffff812ba924>] call_netdevice_notifiers+0x16/0x18
>  [<ffffffff812bac22>] __dev_notify_flags+0x37/0x5b
>  [<ffffffff812bac8c>] dev_change_flags+0x46/0x52
>  [<ffffffff812c41af>] do_setlink+0x250/0x3cd
>  [<ffffffff812c4ee8>] rtnl_newlink+0x2b6/0x49d
>  [<ffffffff812c4cdd>] ? rtnl_newlink+0xab/0x49d
>  [<ffffffff812c4c17>] rtnetlink_rcv_msg+0x1b7/0x1d2
>  [<ffffffff812c4a60>] ? rtnetlink_rcv_msg+0x0/0x1d2
>  [<ffffffff812cc1dc>] netlink_rcv_skb+0x3e/0x8f
>  [<ffffffff812c4a59>] rtnetlink_rcv+0x21/0x28
>  [<ffffffff812cbefe>] netlink_unicast+0x218/0x28f
>  [<ffffffff812cc76e>] netlink_sendmsg+0x26b/0x27a
>  [<ffffffff812a9f1d>] sock_sendmsg+0xd4/0xf5
>  [<ffffffff81096dca>] ? might_fault+0x4e/0x9e
>  [<ffffffff81096dca>] ? might_fault+0x4e/0x9e
>  [<ffffffff81096e13>] ? might_fault+0x97/0x9e
>  [<ffffffff81096dca>] ? might_fault+0x4e/0x9e
>  [<ffffffff812b4122>] ? verify_iovec+0x59/0x97
>  [<ffffffff812aa1d9>] sys_sendmsg+0x209/0x273
>  [<ffffffff810976dc>] ? __do_fault+0x395/0x3cd
>  [<ffffffff8109928f>] ? handle_mm_fault+0x324/0x69d
>  [<ffffffff81051e4e>] ? trace_hardirqs_on_caller+0x10c/0x130
>  [<ffffffff81074972>] ? audit_syscall_entry+0x17d/0x1b0
>  [<ffffffff81364154>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>  [<ffffffff81001eeb>] system_call_fastpath+0x16/0x1b
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
> 
>  net/netlabel/netlabel_unlabeled.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
> index 852d9d7..7ea64e4 100644
> --- a/net/netlabel/netlabel_unlabeled.c
> +++ b/net/netlabel/netlabel_unlabeled.c
> @@ -799,6 +799,7 @@ static int netlbl_unlhsh_netdev_handler(struct notifier_block *this,
>  
>  	/* XXX - should this be a check for NETDEV_DOWN or _UNREGISTER? */
>  	if (event == NETDEV_DOWN) {
> +		rcu_read_lock();
>  		spin_lock(&netlbl_unlhsh_lock);
>  		iface = netlbl_unlhsh_search_iface(dev->ifindex);
>  		if (iface != NULL && iface->valid) {
> @@ -807,6 +808,7 @@ static int netlbl_unlhsh_netdev_handler(struct notifier_block *this,
>  		} else
>  			iface = NULL;
>  		spin_unlock(&netlbl_unlhsh_lock);
> +		rcu_read_unlock();
>  	}
>  
>  	if (iface != NULL)
> 
> --

Sorry this is not the right fix.

Fix is to change the dereference check to take into account the lock
owned here.