Re: [PATCH 02/10] bpf: Add multi kprobe link

Jiri Olsa
2022-03-08T14:21:52Z

On Mon, Mar 07, 2022 at 05:23:34PM -0800, Andrii Nakryiko wrote:
> On Sun, Mar 6, 2022 at 9:28 AM Jiri Olsa <olsajiri@gmail.com> wrote:
> >
> > On Fri, Mar 04, 2022 at 03:11:01PM -0800, Andrii Nakryiko wrote:
> >
> > SNIP
> >
> > > > +static int
> > > > +kprobe_multi_resolve_syms(const void *usyms, u32 cnt,
> > > > + unsigned long *addrs)
> > > > +{
> > > > + unsigned long addr, size;
> > > > + const char **syms;
> > > > + int err = -ENOMEM;
> > > > + unsigned int i;
> > > > + char *func;
> > > > +
> > > > + size = cnt * sizeof(*syms);
> > > > + syms = kvzalloc(size, GFP_KERNEL);
> > > > + if (!syms)
> > > > + return -ENOMEM;
> > > > +
> > > > + func = kmalloc(KSYM_NAME_LEN, GFP_KERNEL);
> > > > + if (!func)
> > > > + goto error;
> > > > +
> > > > + if (copy_from_user(syms, usyms, size)) {
> > > > + err = -EFAULT;
> > > > + goto error;
> > > > + }
> > > > +
> > > > + for (i = 0; i < cnt; i++) {
> > > > + err = strncpy_from_user(func, syms[i], KSYM_NAME_LEN);
> > > > + if (err == KSYM_NAME_LEN)
> > > > + err = -E2BIG;
> > > > + if (err < 0)
> > > > + goto error;
> > > > +
> > > > + err = -EINVAL;
> > > > + if (func[0] == '\0')
> > > > + goto error;
> > >
> > > wouldn't empty string be handled by kallsyms_lookup_name?
> >
> > it would scan and compare all symbols with empty string,
> > so it's better to test for it
>
> I don't mind, but it seems like kallsyms_lookup_name() should be made
> smarter than that instead, no?

true, I'll do that

jirka