[for-linus][PATCH 1/8] tracing: Fix trace_check_vprintf() when tp_printk is used

From: Steven Rostedt
Date: Fri Oct 04 2024 - 09:56:51 EST


From: Steven Rostedt <rostedt@xxxxxxxxxxx>

When the tp_printk kernel command line is used, the trace events go
directly to printk(). It is still checked via the trace_check_vprintf()
function to make sure the pointers of the trace event are legit.

The addition of reading buffers from previous boots required adding a
delta between the addresses of the previous boot and the current boot so
that the pointers in the old buffer can still be used. But this required
adding a trace_array pointer to acquire the delta offsets.

The tp_printk code does not provide a trace_array (tr) pointer, so when
the offsets were examined, a NULL pointer dereference happened and the
kernel crashed.

If the trace_array does not exist, just default the delta offsets to zero,
as that also means the trace event is not being read from a previous boot.

Link: https://lore.kernel.org/all/Zv3z5UsG_jsO9_Tb@xxxxxxxxxxxxxxxxxx/

Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Link: https://lore.kernel.org/20241003104925.4e1b1fd9@xxxxxxxxxxxxxxxxxx
Fixes: 07714b4bb3f98 ("tracing: Handle old buffer mappings for event strings and functions")
Reported-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Tested-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
kernel/trace/trace.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c01375adc471..1c69ca1f1088 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3697,8 +3697,8 @@ static void test_can_verify(void)
void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
va_list ap)
{
- long text_delta = iter->tr->text_delta;
- long data_delta = iter->tr->data_delta;
+ long text_delta = 0;
+ long data_delta = 0;
const char *p = fmt;
const char *str;
bool good;
@@ -3710,6 +3710,17 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
if (static_branch_unlikely(&trace_no_verify))
goto print;

+ /*
+ * When the kernel is booted with the tp_printk command line
+ * parameter, trace events go directly through to printk().
+ * It also is checked by this function, but it does not
+ * have an associated trace_array (tr) for it.
+ */
+ if (iter->tr) {
+ text_delta = iter->tr->text_delta;
+ data_delta = iter->tr->data_delta;
+ }
+
/* Don't bother checking when doing a ftrace_dump() */
if (iter->fmt == static_fmt_buf)
goto print;
--
2.45.2