On Wed, Jul 30, 2025 at 04:13:25PM -0700, Alexei Starovoitov wrote:
> On Wed, Jul 30, 2025 at 4:09 PM Kees Cook <k...@kernel.org> wrote:
> >
> > On Wed, Jul 30, 2025 at 04:07:33PM -0700, Alexei Starovoitov wrote:
> > > On Wed, Jul 30, 2025 at 4:02 PM Kees Cook <k...@kernel.org> wrote:
> > > >
> > > > On Thu, Jul 03, 2025 at 01:48:14PM -0700, Kumar Kartikeya Dwivedi wrote:
> > > > > +static void bpf_prog_report_rqspinlock_violation(const char *str,
> > > > > void *lock, bool irqsave)
> > > > > +{
> > > > > + struct rqspinlock_held *rqh =
> > > > > this_cpu_ptr(&rqspinlock_held_locks);
> > > > > + struct bpf_stream_stage ss;
> > > > > + struct bpf_prog *prog;
> > > > > +
> > > > > + prog = bpf_prog_find_from_stack();
> > > > > + if (!prog)
> > > > > + return;
> > > > > + bpf_stream_stage(ss, prog, BPF_STDERR, ({
> > > > > + bpf_stream_printk(ss, "ERROR: %s for
> > > > > bpf_res_spin_lock%s\n", str, irqsave ? "_irqsave" : "");
> > > > > + bpf_stream_printk(ss, "Attempted lock = 0x%px\n",
> > > > > lock);
> > > > > + bpf_stream_printk(ss, "Total held locks = %d\n",
> > > > > rqh->cnt);
> > > > > + for (int i = 0; i < min(RES_NR_HELD, rqh->cnt); i++)
> > > > > + bpf_stream_printk(ss, "Held lock[%2d] =
> > > > > 0x%px\n", i, rqh->locks[i]);
> > > > > + bpf_stream_dump_stack(ss);
> > > >
> > > > Please don't include %px in stuff going back to userspace in standard
> > > > error reporting. That's a kernel address leak:
> > > > https://docs.kernel.org/process/deprecated.html#p-format-specifier
> > > >
> > > > I don't see any justification here, please remove the lock address or
> > > > use regular %p to get a hashed value.
> > >
> > > There is no leak here.
> > > The prog was loaded by root and error is read by root.
> >
> > uid has nothing to do with it. Leaking addresses needs the right
> > capability set. Is that always true here?
>
> yes. For bpf prog to use this kfunc it needs CAP_BPF and CAP_PERMON.
> What's allowed under them is described in include/uapi/linux/capability.h
Okay, thanks! That wasn't detailed in the commit log (for folks like me
with less familiarity with BPF), so I just got worried when I saw
"stderr" mentioned. :)
--
Kees Cook
