lkml.org 
[lkml]   [2022]   [Jan]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH v8 11/12] user_events: Validate user payloads for size and null termination
Hi Beau,

On Mon, 3 Jan 2022 10:53:08 -0800
Beau Belgrave <beaub@linux.microsoft.com> wrote:

[...]
> > > typedef void (*user_event_func_t) (struct user_event *user, struct iov_iter *i,
> > > - void *tpdata);
> > > + void *tpdata, bool *faulted);
> >
> > Why don't you just return "int" value? ;-)
> >
>
> There can be more than one callback attached per-probe, and in all cases
> where a return value is needed is for a faulted (or would have faulted)
> case. This allows less branches when data is being traced/logged as the
> return value does not need to be checked (nor should it short circuit
> other probes that are attached).

Would you mean overwriting the 'faulted' ? If so, you can do something like

faulted = 0;
for_each_user_event_func(user_event_func) {
faulted |= user_event_func();
}
if (faulted)
...

But I think if one user_event_func() fails to access the user data,
other funcs also fail. In this case, it is faster to skip others than
repeating faults.

[...]
> > > @@ -555,19 +648,25 @@ static void user_event_ftrace(struct user_event *user, struct iov_iter *i,
> > > return;
> > >
> > > /* Allocates and fills trace_entry, + 1 of this is data payload */
> > > - entry = trace_event_buffer_reserve(&event_buffer, file,
> > > - sizeof(*entry) + i->count);
> > > + entry = trace_event_buffer_reserve(&event_buffer, file, size);
> > >
> > > if (unlikely(!entry))
> > > return;
> > >
> > > - if (unlikely(!copy_nofault(entry + 1, i->count, i))) {
> > > - __trace_event_discard_commit(event_buffer.buffer,
> > > - event_buffer.event);
> > > - return;
> > > - }
> > > + if (unlikely(!copy_nofault(entry + 1, i->count, i)))
> > > + goto discard;
> >
> > OK, this is a fault error.
> >
> > > +
> > > + if (!list_empty(&user->validators) &&
> > > + unlikely(user_event_validate(user, entry, size)))
> > > + goto discard;
> >
> > But this maybe an invalid parameter error.
> >
>
> Yes, but it has to be an invalid parameter that would have caused a
> possible fault in a worse place. In my mind, I still treat it as a fault
> case whether the user did it intentionally or not :)

OK, I got it.

Thank you,

>
> Thanks,
> -Beau


--
Masami Hiramatsu <mhiramat@kernel.org>

\
 
 \ /
  Last update: 2022-01-07 00:33    [W:0.055 / U:0.440 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site