tracing: Reject string operand in the histogram expression

Since the string type can not be the target of the addition / subtraction
operation, it must be rejected. Without this fix, the string type silently
converted to digits.

Link: https://lkml.kernel.org/r/162742654278.290973.1523000673366456634.stgit@devnote2

Cc: stable@vger.kernel.org
Fixes: 100719dcef ("tracing: Add simple expression support to hist triggers")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -65,7 +65,8 @@
 	C(INVALID_SORT_MODIFIER,"Invalid sort modifier"),		\
 	C(EMPTY_SORT_FIELD,	"Empty sort field"),			\
 	C(TOO_MANY_SORT_FIELDS,	"Too many sort fields (Max = 2)"),	\
-	C(INVALID_SORT_FIELD,	"Sort field must be a key or a val"),
+	C(INVALID_SORT_FIELD,	"Sort field must be a key or a val"),	\
+	C(INVALID_STR_OPERAND,	"String type can not be an operand in expression"),
 
 #undef C
 #define C(a, b)		HIST_ERR_##a
@@ -2156,6 +2157,13 @@ static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
 		ret = PTR_ERR(operand1);
 		goto free;
 	}
+	if (operand1->flags & HIST_FIELD_FL_STRING) {
+		/* String type can not be the operand of unary operator. */
+		hist_err(file->tr, HIST_ERR_INVALID_STR_OPERAND, errpos(str));
+		destroy_hist_field(operand1, 0);
+		ret = -EINVAL;
+		goto free;
+	}
 
 	expr->flags |= operand1->flags &
 		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);
@@ -2257,6 +2265,11 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		operand1 = NULL;
 		goto free;
 	}
+	if (operand1->flags & HIST_FIELD_FL_STRING) {
+		hist_err(file->tr, HIST_ERR_INVALID_STR_OPERAND, errpos(operand1_str));
+		ret = -EINVAL;
+		goto free;
+	}
 
 	/* rest of string could be another expression e.g. b+c in a+b+c */
 	operand_flags = 0;
@@ -2266,6 +2279,11 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		operand2 = NULL;
 		goto free;
 	}
+	if (operand2->flags & HIST_FIELD_FL_STRING) {
+		hist_err(file->tr, HIST_ERR_INVALID_STR_OPERAND, errpos(str));
+		ret = -EINVAL;
+		goto free;
+	}
 
 	ret = check_expr_operands(file->tr, operand1, operand2);
 	if (ret)