RE: KASAN+netlink, was: [PATCH] [net-next?] hns: avoid stack overflow with CONFIG_KASAN

From: David Laight
Date: Wed Feb 08 2017 - 11:42:05 EST

> From: Johannes Berg
> Sent: 08 February 2017 12:24
> Btw, what's causing this to start with? Can't the compiler reuse the
> stack places?

Only if it realises they've gone out of scope - which probably
doesn't happen when the functions are inlined.
The address of the parameter can be saved by the calling function
and used in a later call.

Something like this is valid:

int foo(int *p, int v)
static int *sv;
int old = -1;
if (sv) {old = *sv; *sv = v;}
sv = v;
return old;

void bar(...) {
int a, b;
foo(&a, 0);
foo(&b, 1);
foo(NULL, 2);

If the compiler starts sharing stack it all goes wrong.