Re: [PATCH bpf-next 3/3] bpf: Force cookies array to follow symbols sorting

[Andrii Nakryiko]

On Thu, Jun 2, 2022 at 4:01 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Fri, May 27, 2022 at 1:57 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > When user specifies symbols and cookies for kprobe_multi link
> > interface it's very likely the cookies will be misplaced and
> > returned to wrong functions (via get_attach_cookie helper).
> >
> > The reason is that to resolve the provided functions we sort
> > them before passing them to ftrace_lookup_symbols, but we do
> > not do the same sort on the cookie values.
> >
> > Fixing this by using sort_r function with custom swap callback
> > that swaps cookie values as well.
> >
> > Fixes: 0236fec57a15 ("bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link")
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> >  kernel/trace/bpf_trace.c | 65 ++++++++++++++++++++++++++++++----------
> >  1 file changed, 50 insertions(+), 15 deletions(-)
> >
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 10b157a6d73e..e5c423b835ab 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -2423,7 +2423,12 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,
> >         kprobe_multi_link_prog_run(link, entry_ip, regs);
> >  }
> >
> > -static int symbols_cmp(const void *a, const void *b)
> > +struct multi_symbols_sort {
> > +       const char **funcs;
> > +       u64 *cookies;
> > +};
> > +
> > +static int symbols_cmp_r(const void *a, const void *b, const void *priv)
> >  {
> >         const char **str_a = (const char **) a;
> >         const char **str_b = (const char **) b;
> > @@ -2431,6 +2436,25 @@ static int symbols_cmp(const void *a, const void *b)
> >         return strcmp(*str_a, *str_b);
> >  }
> >
> > +static void symbols_swap_r(void *a, void *b, int size, const void *priv)
> > +{
> > +       const struct multi_symbols_sort *data = priv;
> > +       const char **name_a = a, **name_b = b;
> > +       u64 *cookie_a, *cookie_b;
> > +
> > +       cookie_a = data->cookies + (name_a - data->funcs);
> > +       cookie_b = data->cookies + (name_b - data->funcs);
> > +
> > +       /* swap name_a/name_b and cookie_a/cookie_b values */
> > +       swap(*name_a, *name_b);
> > +       swap(*cookie_a, *cookie_b);
> > +}
> > +
> > +static int symbols_cmp(const void *a, const void *b)
> > +{
> > +       return symbols_cmp_r(a, b, NULL);
> > +}
> > +
> >  int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> >  {
> >         struct bpf_kprobe_multi_link *link = NULL;
> > @@ -2468,6 +2492,19 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> >         if (!addrs)
> >                 return -ENOMEM;
> >
> > +       ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
> > +       if (ucookies) {
> > +               cookies = kvmalloc(size, GFP_KERNEL);

oh, and you'll have to rebase anyways after kvmalloc_array patch

> > +               if (!cookies) {
> > +                       err = -ENOMEM;
> > +                       goto error;
> > +               }
> > +               if (copy_from_user(cookies, ucookies, size)) {
> > +                       err = -EFAULT;
> > +                       goto error;
> > +               }
> > +       }
> > +
> >         if (uaddrs) {
> >                 if (copy_from_user(addrs, uaddrs, size)) {
> >                         err = -EFAULT;
> > @@ -2480,26 +2517,24 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> >                 if (err)
> >                         goto error;
> >
> > -               sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL);
> > +               if (cookies) {
> > +                       struct multi_symbols_sort data = {
> > +                               .cookies = cookies,
> > +                               .funcs = us.syms,
> > +                       };
> > +
> > +                       sort_r(us.syms, cnt, sizeof(*us.syms), symbols_cmp_r,
> > +                              symbols_swap_r, &data);
> > +               } else {
> > +                       sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL);
> > +               }
>
> maybe just always do sort_r, swap callback can just check if cookie
> array is NULL and if not, additionally swap cookies? why have all
> these different callbacks and complicate the code unnecessarily?
>
> > +
> >                 err = ftrace_lookup_symbols(us.syms, cnt, addrs);
> >                 free_user_syms(&us);
> >                 if (err)
> >                         goto error;
> >         }
> >
> > -       ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
> > -       if (ucookies) {
> > -               cookies = kvmalloc(size, GFP_KERNEL);
> > -               if (!cookies) {
> > -                       err = -ENOMEM;
> > -                       goto error;
> > -               }
> > -               if (copy_from_user(cookies, ucookies, size)) {
> > -                       err = -EFAULT;
> > -                       goto error;
> > -               }
> > -       }
> > -
> >         link = kzalloc(sizeof(*link), GFP_KERNEL);
> >         if (!link) {
> >                 err = -ENOMEM;
> > --
> > 2.35.3
> >