On Tue 2025-11-18 18:16:23, Richard W.M. Jones wrote:
> On Tue, Nov 18, 2025 at 06:56:33PM +0100, Pavel Machek wrote:
> > Hi!
> > 
> > > Recently, syzbot started to abuse NBD with all kinds of sockets.
> > > 
> > > Commit cf1b2326b734 ("nbd: verify socket is supported during setup")
> > > made sure the socket supported a shutdown() method.
> > > 
> > > Explicitely accept TCP and UNIX stream sockets.
> > 
> > Note that running nbd server and client on same machine is not safe in
> > read-write mode. It may deadlock under low memory conditions.
> > 
> > Thus I'm not sure if we should accept UNIX sockets.
> 
> Both nbd-client and nbdkit have modes where they can mlock themselves
> into RAM.

kernel needs memory. It issues write-back to get some.
nbd-client does syscall. Maybe writing to storage?
That syscall does kmalloc().
That kmalloc now needs something like PF_MEMALLOC flag.

mlock() is not enough.

Best regards,
							Pavel
-- 
I don't work for Nazis and criminals, and neither should you.
Boycott Putin, Trump, Netanyahu and Musk!