[PATCH 4.19.y] tracing: Reject string operand in the histogram expression

[Masami Hiramatsu <mhiramat@kernel.org>]

commit a9d10ca4986571bffc19778742d508cc8dd13e02 upstream

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: 100719dcef447 ("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>
---
 - Since there is no hist_err() APIs in 4.19, this just check the flag
   and return an error without any error messages.
---
 kernel/trace/trace_events_hist.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 28e4ff45cb4c..e9106c976a48 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2781,6 +2781,12 @@ 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. */
+		destroy_hist_field(operand1, 0);
+		ret = -EINVAL;
+		goto free;
+	}
 
 	expr->flags |= operand1->flags &
 		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);
@@ -2881,6 +2887,10 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		operand1 = NULL;
 		goto free;
 	}
+	if (operand1->flags & HIST_FIELD_FL_STRING) {
+		ret = -EINVAL;
+		goto free;
+	}
 
 	/* rest of string could be another expression e.g. b+c in a+b+c */
 	operand_flags = 0;
@@ -2890,6 +2900,10 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		operand2 = NULL;
 		goto free;
 	}
+	if (operand2->flags & HIST_FIELD_FL_STRING) {
+		ret = -EINVAL;
+		goto free;
+	}
 
 	ret = check_expr_operands(operand1, operand2);
 	if (ret)