[PATCH v2] tracing: Add a helper function to handle the dereference arg in verifier

[Steven Rostedt <rostedt@goodmis.org>]

From: Steven Rostedt <rostedt@goodmis.org>

Add a helper function called handle_dereference_arg() to replace the logic
that is identical in two locations of test_event_printk().

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v1: https://lore.kernel.org/20250424151021.44b68ba8@gandalf.local.home

- Fixed order of parameters in handle_dereference_arg() as len and
  string_flags were reversed, causing it to fail on pretty much all events!
  I did post v1 because it was sitting in my repo and I needed to do more
  work on other things in that repo, but I obviously never tested it!

 kernel/trace/trace_events.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 069e92856bda..13cb899ba4fc 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -400,6 +400,20 @@ static bool process_string(const char *fmt, int len, struct trace_event_call *ca
 	return true;
 }
 
+static void handle_dereference_arg(const char *arg_str, u64 string_flags, int len,
+				   u64 *dereference_flags, int arg,
+				   struct trace_event_call *call)
+{
+	if (string_flags & (1ULL << arg)) {
+		if (process_string(arg_str, len, call))
+			*dereference_flags &= ~(1ULL << arg);
+	} else if (process_pointer(arg_str, len, call))
+		*dereference_flags &= ~(1ULL << arg);
+	else
+		pr_warn("TRACE EVENT ERROR: Bad dereference argument: '%.*s'\n",
+			len, arg_str);
+}
+
 /*
  * Examine the print fmt of the event looking for unsafe dereference
  * pointers using %p* that could be recorded in the trace event and
@@ -563,11 +577,9 @@ static void test_event_printk(struct trace_event_call *call)
 			}
 
 			if (dereference_flags & (1ULL << arg)) {
-				if (string_flags & (1ULL << arg)) {
-					if (process_string(fmt + start_arg, e - start_arg, call))
-						dereference_flags &= ~(1ULL << arg);
-				} else if (process_pointer(fmt + start_arg, e - start_arg, call))
-					dereference_flags &= ~(1ULL << arg);
+				handle_dereference_arg(fmt + start_arg, string_flags,
+						       e - start_arg,
+						       &dereference_flags, arg, call);
 			}
 
 			start_arg = i;
@@ -578,11 +590,9 @@ static void test_event_printk(struct trace_event_call *call)
 	}
 
 	if (dereference_flags & (1ULL << arg)) {
-		if (string_flags & (1ULL << arg)) {
-			if (process_string(fmt + start_arg, i - start_arg, call))
-				dereference_flags &= ~(1ULL << arg);
-		} else if (process_pointer(fmt + start_arg, i - start_arg, call))
-			dereference_flags &= ~(1ULL << arg);
+		handle_dereference_arg(fmt + start_arg, string_flags,
+				       i - start_arg,
+				       &dereference_flags, arg, call);
 	}
 
 	/*
-- 
2.47.2