From: Pavel Machek <pavel@ucw.cz>
To: "Richard W.M. Jones" <rjones@redhat.com>,
akpm@linux-foundation.org, david@kernel.org,
lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com,
rppt@kernel.org, vbabka@suse.cz, surenb@google.com,
mhocko@suse.com, linux-mm@kvack.org
Cc: Eric Dumazet <edumazet@google.com>,
Josef Bacik <josef@toxicpanda.com>, Jens Axboe <axboe@kernel.dk>,
linux-kernel <linux-kernel@vger.kernel.org>,
netdev@vger.kernel.org, Eric Dumazet <eric.dumazet@gmail.com>,
syzbot+e1cd6bd8493060bd701d@syzkaller.appspotmail.com,
Mike Christie <mchristi@redhat.com>,
Yu Kuai <yukuai1@huaweicloud.com>,
linux-block@vger.kernel.org, nbd@other.debian.org
Subject: Userland used in writeback path was Re: [PATCH] nbd: restrict sockets to TCP and UDP
Date: Wed, 19 Nov 2025 10:10:37 +0100 [thread overview]
Message-ID: <aR2JjR1yKHCCPalO@duo.ucw.cz> (raw)
In-Reply-To: <20251118181623.GK1427@redhat.com>
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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.
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next parent reply other threads:[~2025-11-19 9:10 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20250909132243.1327024-1-edumazet@google.com>
[not found] ` <aRyzUc/WndKJBAz0@duo.ucw.cz>
[not found] ` <20251118181623.GK1427@redhat.com>
2025-11-19 9:10 ` Pavel Machek [this message]
2025-11-24 11:04 ` Richard W.M. Jones
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