netdev - Re: [PATCH net v3 1/7] net/sched: act_gate: zero-initialize netlink dump struct

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Message-ID: <YAOV0f1EtmF5tiEGoQMdsnQAKJSrqcg3h9hqnxDdba8MmAprjNHfcDBKselH1vYNZLb672n_zDJZpgjkVn0nHDS0Jh7BKQrh0uGwJYp2hEk=@1g4.org>
Date: Wed, 21 Jan 2026 14:01:01 +0000
From: Paul Moses <p@....org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net v3 1/7] net/sched: act_gate: zero-initialize netlink dump struct

padding? why does fzero-init-padding-bits exist?

On Wednesday, January 21st, 2026 at 7:48 AM, Eric Dumazet <edumazet@...gle.com> wrote:

> 
> 
> On Wed, Jan 21, 2026 at 2:39 PM Paul Moses p@....org wrote:
> 
> > Yes, it's not proven so you might be right, I knew it was 4 bytes at best. We can do next or toss it, I don't feel strongly either way.
> 
> 
> These bytes are cleared by C compilers.
> 
> https://en.cppreference.com/w/c/language/struct_initialization.html
> 
> Only holes might be left uninitialized.
> 
> > On Wednesday, January 21st, 2026 at 7:25 AM, Eric Dumazet edumazet@...gle.com wrote:
> > 
> > > On Wed, Jan 21, 2026 at 2:20 PM Paul Moses p@....org wrote:
> > > 
> > > > Zero-initialize the dump struct before selective assignment to avoid
> > > > leaking stack padding in netlink replies. This matches other actions
> > > > (e.g. act_connmark) that zero-init their dump structs.
> > > > 
> > > > Fixes: a51c328df310 ("net: qos: introduce a gate control flow action")
> > > > Cc: stable@...r.kernel.org
> > > > Signed-off-by: Paul Moses p@....org
> > > > ---
> > > 
> > > I do not see a bug to fix, current code is fine.
> > > 
> > > act_connmark problem was that "struct tc_connmark" had a 16bit hole.
> > > 
> > > No such issue for struct tc_gate.