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Commit 55267c88 authored by Tom Zanussi's avatar Tom Zanussi Committed by Steven Rostedt (VMware)
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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/64ec8dc15c14d305295b64cdfcc6b2b9dd14753f.1555597045.git.tom.zanussi@linux.intel.com



Reported-by: default avatarVincent Bernat <vincent@bernat.ch>
Signed-off-by: default avatarTom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent a188339c

kernel/trace/trace_events_hist.c

+3 −0
Original line number Diff line number Diff line
@@ -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];