On Wed, 6 Jun 2012 11:21:27 +0800 Wanpeng Li <liwp.linux@xxxxxxxxx> wrote: > >Secondly, this code will permit unprivileged users to flood the logs, > >by repeatedly reading /proc/sys/vm/nr_pdflush_threads. We try to avoid > >this, as it is a form of denial-of-service attack. > > > >This is a bit hard to fix. The typical way of addressing this is to > >use printk_once(), so the message only appears once per boot. But that > >doesn't work for a generic function - we'd need to add one bit of state > >to the ctl_table to do this. We can of course do that, but it's not > >obvious that it's _worth_ doing that just for handling obsolete > >entries. > > > >So perhaps the solution is to give up on the generic proc_obsolete() > >idea, and just add a handler specifically for nr_pdflush_threads, whcih > >uses printk_once(). > > What about modify the generic proc_obsolete just to put the warning message into > the buffer, then transfer to userspace, in order to users can see this warning.Do > you think this is a better idea? err, no. That's deliberately corrupting the output of an existing interface. In response to this change userspace might crash, hand over root privileges or tune to a porn channel. Instead we should yield a well-formed response such as "0" (or maybe non-zero, if a zero response might be unexpected) and inform the system operator via conventional means. ie: syslog. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
