[PATCH] um: fix execve stub execution on old host OSs

[Benjamin Berg]

On Mon, 2025-06-09 at 19:15 +0200, Johannes Berg wrote:
> On Sun, 2025-06-08 at 20:38 +0200, Benjamin Berg wrote:
> > > 
> > > But my host kernel is 5.4 and fails to compile these pieces of
> > > codes because
> > > there is no this syscall in my older kernel.
> > > 
> > > I was wondering if you are working on this issue. If not, I will
> > > try to 
> > > make a draft solution to review.
> > 
> > I was not yet aware of that problem. Most likely only the one in
> > start_up.c is a problem for you. All the other ones probably pick
> > up
> > the correct definition from the Linux tree already.
> > 
> > One can probably solve it by moving the code into another file. Or
> > maybe by adding an entry for __NR_close_range into common-offests.h
> > and
> > using that.
> 
> Seems though we might need to add checking for close_range to the
> seccomp init though, it's actually (much) newer than seccomp. Or just
> not rely on it?

That check is what is failing now :-)

We already introduced close_range use earlier, but in ptrace mode it is
just about hygiene rather than actually being safety relevant. So we
just accept the syscall failure there.

Benjamin