On Thu, Aug 10, 2023 at 04:38:21PM +0200, Martin Uecker wrote:
> Am Donnerstag, dem 10.08.2023 um 13:59 +0000 schrieb Qing Zhao:
> >
> > > On Aug 10, 2023, at 2:58 AM, Martin Uecker <muec...@gwdg.de> wrote:
> > >
> > > Am Mittwoch, dem 09.08.2023 um 20:10 +0000 schrieb Qing Zhao:
> > > >
> > > > > On Aug 9, 2023, at 12:21 PM, Michael Matz <m...@suse.de> wrote:
> > >
>
> > > I am not sure for the reason given above. The following
> > > code would not work:
> > >
> > > struct foo_flex { int a; short b; char t[]; } x;
> > > x.a = 1;
> > > struct foo_flex *p = malloc(sizeof(x) + x.a);
> > > if (!p) abort();
> > > memcpy(p, &x, sizeof(x)); // initialize struct
> > >
> > Okay.
> > Then, the user still should use the sizeof(struct foo_flex) + N *
> > sizeof(foo->t) for the allocation, even though this might allocate more
> > bytes than necessary. (But this is safe)
> >
> > Let me know if I still miss anything.
>
> The question is not only what the user should use to
> allocate, but also what BDOS should return. In my
> example the user uses the sizeof() + N * sizeof
> formula and the memcpy is safe, but it would be flagged
> as a buffer overrun if BDOS uses the offsetof formula.
BDOS/BOS (at least the 0 level) should return what is actually
allocated for the var, what size was passed to malloc and if it
is a var with flex array member with initialization what is actually the
size on the stack or in .data/.rodata etc.
And for 1 level the same unless it is just access to some element, then
it should be capped by the size of that element.
Jakub
