This Linux kernel change "tracing: Prevent hist_field_var_ref() from accessing NULL tracing_map_elts" is included in the Linux 5.2 release. This change is authored by Tom Zanussi <tom.zanussi [at] linux.intel.com> on Thu Apr 18 10:18:50 2019 -0500. The commit for this change in Linux stable tree is 55267c8 (patch).
tracing: Prevent hist_field_var_ref() from accessing NULL tracing_map_elts hist_field_var_ref() is an implementation of hist_field_fn_t(), which can be called with a null tracing_map_elt elt param when assembling a key in event_hist_trigger(). In the case of hist_field_var_ref() this doesn't make sense, because a variable can only be resolved by looking it up using an already assembled key i.e. a variable can't be used to assemble a key since the key is required in order to access the variable. Upper layers should prevent the user from constructing a key using a variable in the first place, but in case one slips through, it shouldn't cause a NULL pointer dereference. Also if one does slip through, we want to know about it, so emit a one-time warning in that case. Link: http://lkml.kernel.org/r/64ec[email protected]linux.intel.com Reported-by: Vincent Bernat <[email protected]> Signed-off-by: Tom Zanussi <[email protected]> Signed-off-by: Steven Rostedt (VMware) <[email protected]>
There are 3 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.
kernel/trace/trace_events_hist.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 7fca345..06e7b9f 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -1854,6 +1854,9 @@ static u64 hist_field_var_ref(struct hist_field *hist_field, struct hist_elt_data *elt_data; u64 var_val = 0; + if (WARN_ON_ONCE(!elt)) + return var_val; + elt_data = elt->private_data; var_val = elt_data->var_ref_vals[hist_field->var_ref_idx];