pending-4.19/tracing-prevent-hist_field_var_ref-from-accessing-nu.patch

   1 From 9d5ad9072bd55982fef63a2e02fcbdd0399600b0 Mon Sep 17 00:00:00 2001
   2 From: Tom Zanussi <tom.zanussi@linux.intel.com>
   3 Date: Thu, 18 Apr 2019 10:18:50 -0500
   4 Subject: tracing: Prevent hist_field_var_ref() from accessing NULL
   5  tracing_map_elts
   6
   7 [ Upstream commit 55267c88c003a3648567beae7c90512d3e2ab15e ]
   8
   9 hist_field_var_ref() is an implementation of hist_field_fn_t(), which
  10 can be called with a null tracing_map_elt elt param when assembling a
  11 key in event_hist_trigger().
  12
  13 In the case of hist_field_var_ref() this doesn't make sense, because a
  14 variable can only be resolved by looking it up using an already
  15 assembled key i.e. a variable can't be used to assemble a key since
  16 the key is required in order to access the variable.
  17
  18 Upper layers should prevent the user from constructing a key using a
  19 variable in the first place, but in case one slips through, it
  20 shouldn't cause a NULL pointer dereference.  Also if one does slip
  21 through, we want to know about it, so emit a one-time warning in that
  22 case.
  23
  24 Link: http://lkml.kernel.org/r/64ec8dc15c14d305295b64cdfcc6b2b9dd14753f.1555597045.git.tom.zanussi@linux.intel.com
  25
  26 Reported-by: Vincent Bernat <vincent@bernat.ch>
  27 Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
  28 Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
  29 Signed-off-by: Sasha Levin <sashal@kernel.org>
  30 ---
  31  kernel/trace/trace_events_hist.c | 3 +++
  32  1 file changed, 3 insertions(+)
  33
  34 diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
  35 index 11853e90b649..3f34cfb66a85 100644
  36 --- a/kernel/trace/trace_events_hist.c
  37 +++ b/kernel/trace/trace_events_hist.c
  38 @@ -1632,6 +1632,9 @@ static u64 hist_field_var_ref(struct hist_field *hist_field,
  39         struct hist_elt_data *elt_data;
  40         u64 var_val = 0;
  41
  42 +       if (WARN_ON_ONCE(!elt))
  43 +               return var_val;
  44 +
  45         elt_data = elt->private_data;
  46         var_val = elt_data->var_ref_vals[hist_field->var_ref_idx];
  47
  48 --
  49 2.20.1
  50