[for-linus][PATCH 3/3] tracing/histogram: Fix check for missing operands in an expression

[Steven Rostedt]

From: Kalesh Singh <kaleshsingh@xxxxxxxxxx>

If a binary operation is detected while parsing an expression string,
the operand strings are deduced by splitting the experssion string at
the position of the detected binary operator. Both operand strings are
sub-strings (can be empty string) of the expression string but will
never be NULL.

Currently a NULL check is used for missing operands, fix this by
checking for empty strings instead.

Link: https://lkml.kernel.org/r/20211112191324.1302505-1-kaleshsingh@xxxxxxxxxx

Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Fixes: 9710b2f341a0 ("tracing: Fix operator precedence for hist triggers expression")
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 6a9fa34e2785..1475d7347fe0 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2581,7 +2581,8 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 	operand1_str = str;
 	str = sep+1;
 
-	if (!operand1_str || !str)
+	/* Binary operator requires both operands */
+	if (*operand1_str == '\0' || *str == '\0')
 		goto free;
 
 	operand_flags = 0;
-- 
2.33.0