Evgeniy Polyakov wrote: > On Wed, Apr 18, 2007 at 10:26:31AM +0200, Patrick McHardy ([EMAIL PROTECTED]) > wrote: > >>>Out of curiosity, why not to fix a netlink_dump_start() to remove >>>callback in error path, since in 'no-error' path it removes it in >>>netlink_dump(). >> >> >>It already does (netlink_destroy_callback), but that doesn't help >>with this race though since without this patch we don't enter the >>error path. > > > I thought that with releasing a socket, which will have a callback > attached only results in a leak of the callback? In that case we can > just free it in dump() just like it is done in no-error path already. > Or do I miss something additional?
That would only work if there is nothing to dump (cb->dump returns 0). Otherwise it is not freed. >>The problem is asynchronous processing of the dump request in the >>context of a different process. Process requests a dump, message >>is queued and process returns from sendmsg since some other process >>is already processing the queue. Then the process closes the socket, >>resulting in netlink_release being called. When the dump request >>is finally processed the race Pavel described might happen. This >>can only happen for netlink families that use mutex_try_lock for >>queue processing of course. > > > Doesn't it called from ->sk_data_ready() which is synchronous with > respect to sendmsg, not sure about conntrack though, but it looks so? Yes, but for kernel sockets we end up calling the input function, which when mutex_trylock is used returns immediately when some other process is already processing the queue, so the requesting process might close the socket before the request is processed. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
