[for-linus][PATCH 5/5] tracing: Do not set trace clock if tracefs lockdown is in effect

Steven Rostedt
2020-01-21T14:40:03Z

From: Masami Ichikawa <masami256@gmail.com>

When trace_clock option is not set and unstable clcok detected,
tracing_set_default_clock() sets trace_clock(ThinkPad A285 is one of
case). In that case, if lockdown is in effect, null pointer
dereference error happens in ring_buffer_set_clock().

Link: http://lkml.kernel.org/r/20200116131236.3866925-1-masami256@gmail.com

Cc: stable@vger.kernel.org
Fixes: 17911ff38aa58 ("tracing: Add locked_down checks to the open calls of files created for tracefs")
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1788488
Signed-off-by: Masami Ichikawa <masami256@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ddb7e7f5fe8d..5b6ee4aadc26 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9420,6 +9420,11 @@ __init static int tracing_set_default_clock(void)
{
/* sched_clock_stable() is determined in late_initcall */
if (!trace_boot_clock && !sched_clock_stable()) {
+ if (security_locked_down(LOCKDOWN_TRACEFS)) {
+ pr_warn("Can not set tracing clock due to lockdown\n");
+ return -EPERM;
+ }
+
printk(KERN_WARNING
"Unstable clock detected, switching default tracing clock to \"global\"\n"
"If you want to keep using the local clock, then add:\n"
--
2.24.1