Merge tag 'trace-v5.18-1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull trace event string verifier fix from Steven Rostedt:
 "The run-time string verifier checks all trace event formats as
  they are read from the tracing file to make sure that the %s pointers
  are not reading something that no longer exists.

  However, it failed to account for the valid case of '%*.s' where the
  length given is zero, and the string is NULL. It incorrectly flagged
  it as a null pointer dereference and gave a WARN_ON()"

* tag 'trace-v5.18-1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Have trace event string test handle zero length strings

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 08ea781540b5..f4de111fa18f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3673,12 +3673,17 @@ static char *trace_iter_expand_format(struct trace_iterator *iter)
 }
 
 /* Returns true if the string is safe to dereference from an event */
-static bool trace_safe_str(struct trace_iterator *iter, const char *str)
+static bool trace_safe_str(struct trace_iterator *iter, const char *str,
+			   bool star, int len)
 {
 	unsigned long addr = (unsigned long)str;
 	struct trace_event *trace_event;
 	struct trace_event_call *event;
 
+	/* Ignore strings with no length */
+	if (star && !len)
+		return true;
+
 	/* OK if part of the event data */
 	if ((addr >= (unsigned long)iter->ent) &&
 	    (addr < (unsigned long)iter->ent + iter->ent_size))
@@ -3864,7 +3869,7 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 		 * instead. See samples/trace_events/trace-events-sample.h
 		 * for reference.
 		 */
-		if (WARN_ONCE(!trace_safe_str(iter, str),
+		if (WARN_ONCE(!trace_safe_str(iter, str, star, len),
 			      "fmt: '%s' current_buffer: '%s'",
 			      fmt, show_buffer(&iter->seq))) {
 			int ret;