netdev - Re: [PATCH net-next v2 3/3] netlink: Fix wraparound of sk->sk_rmem

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Message-ID: <20250624071157.3cbb1265@kernel.org>
Date: Tue, 24 Jun 2025 07:11:57 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>
Cc: jbaron@...mai.com, davem@...emloft.net, edumazet@...gle.com,
 horms@...nel.org, kuniyu@...gle.com, netdev@...r.kernel.org, Kuniyuki
 Iwashima <kuni1840@...il.com>
Subject: Re: [PATCH net-next v2 3/3] netlink: Fix wraparound of
 sk->sk_rmem_alloc

On Tue, 24 Jun 2025 09:55:15 +0200 Paolo Abeni wrote:
> > To be clear -- are you saying we should fix this differently?
> > Or perhaps that the problem doesn't exist? The change doesn't
> > seem very intrusive..  
> 
> AFAICS the race is possible even with netlink as netlink_unicast() runs
> without the socket lock, too.
> 
> The point is that for UDP the scenario with multiple threads enqueuing a
> packet into the same socket is a critical path, optimizing for
> performances and allowing some memory accounting inaccuracy makes sense.
> 
> For netlink socket, that scenario looks a patological one and I think we
> should prefer accuracy instead of optimization.

Could you ELI5 what you mean? Are you suggesting a lock around every
sk_rmem write for netlink sockets? 
If we think this is an attack vector the attacker can simply use a UDP
socket instead. Or do you think it'd lead to simpler code?