On Wed, 23 Mar 2022 08:47:10 -0400
Brian Foster <bfoster@xxxxxxxxxx> wrote:
> What's the best way to address this going forward with the memory usage
> verification in place? ISTM we could perhaps consider dropping the
> custom %.*s thing in favor of using %s with __string_len() and friends,
> or perhaps just replace the open-coded NULL parameter with the "(null)"
> string that the trace subsystem code seems to use on NULL pointer
> checks. The latter seems pretty simple and straightforward of a change
> to me, but I want to make sure I'm not missing something more obvious.
> Thoughts?
Can you see if the following (totally untested) patch fixes your issue?
-- Steve
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;
