Re: [PATCH 3.12 69/76] net: fix infoleak in rtnetlink

[David Miller]

From: Vegard Nossum <vegard.nossum@xxxxxxxxx>
Date: Fri, 20 May 2016 14:04:54 +0200

> Just out of curiosity, was this observed in practice? I could be
> wrong, but I was under the impression that using designated
> initializers would zero the rest of the struct, including padding.

I compiled testcases and found that the compiler does not zero out
padding when using designated initializers.

You can do the same.

For example, on sparc 32-bit, this code:

struct foo {
	int a;
	short b;
	int c;
};

extern void foo(struct foo *);

void bar(void)
{
	struct foo f = { .a = 1, .b = 2, .c = 3 };

	foo(&f);
}

gives:

	mov	1, %g1
	st	%g1, [%fp-12]
	mov	2, %g1
	sth	%g1, [%fp-8]
	mov	3, %g1
	st	%g1, [%fp-4]

It does not initialize the padding between 'b' and 'c'.