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

[Eric Dumazet]

On Wed, Jan 21, 2026 at 3:01 PM Paul Moses <p@xxxxxxx> wrote:
>
> padding? why does fzero-init-padding-bits exist?
>

Which padding are you referring to?

$ pahole -C tc_gate --hex  net/sched/act_gate.o
struct tc_gate {
__u32                      index;                /*     0   0x4 */
__u32                      capab;                /*   0x4   0x4 */
int                        action;               /*   0x8   0x4 */
int                        refcnt;               /*   0xc   0x4 */
int                        bindcnt;              /*  0x10   0x4 */

/* size: 20, cachelines: 1, members: 5 */
/* last cacheline: 20 bytes */
};

I see no padding.

>
>
>
> On Wednesday, January 21st, 2026 at 7:48 AM, Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> >
> >
> > On Wed, Jan 21, 2026 at 2:39 PM Paul Moses p@xxxxxxx 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@xxxxxxxxxx wrote:
> > >
> > > > On Wed, Jan 21, 2026 at 2:20 PM Paul Moses p@xxxxxxx 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@xxxxxxxxxxxxxxx
> > > > > Signed-off-by: Paul Moses p@xxxxxxx
> > > > > ---
> > > >
> > > > 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.