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:

quoted

Hi!

quoted

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
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