I should have marked this for stable. The commit it fixes (see Fixes tag) is in 5.4, and it appears this has yet to make it to 5.4 yet.

-- Steve

On Wed, Dec 04, 2019 at 09:05:02PM -0500, Steven Rostedt wrote:

From: "Steven Rostedt (VMware)" rostedt@goodmis.org

If lockdown is disabling tracing on boot up, it prevents the tracing files from even bering created. But when that happens, there's several places that will give a warning that the files were not created as that is usually a sign of a bug.

Add in strategic locations where a check is made to see if tracing is disabled by lockdown, and if it is, do not go further, and fail silently (but print that tracing is disabled by lockdown, without doing a WARN_ON()).

Cc: Matthew Garrett mjg59@google.com Fixes: 17911ff38aa5 ("tracing: Add locked_down checks to the open calls of files created for tracefs") Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org

---

kernel/trace/ring_buffer.c | 6 ++++++ kernel/trace/trace.c | 17 +++++++++++++++++ 2 files changed, 23 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 66358d66c933..4bf050fcfe3b 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -11,6 +11,7 @@ #include <linux/trace_seq.h> #include <linux/spinlock.h> #include <linux/irq_work.h> +#include <linux/security.h> #include <linux/uaccess.h> #include <linux/hardirq.h> #include <linux/kthread.h> /* for self test */ @@ -5068,6 +5069,11 @@ static __init int test_ringbuffer(void) int cpu; int ret = 0;

• if (security_locked_down(LOCKDOWN_TRACEFS)) {

• pr_warning("Lockdown is enabled, skipping ring buffer tests\n");
  

• return 0;
  

• }
• pr_info("Running ring buffer tests...\n");

buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE); diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 02a23a6e5e00..23459d53d576 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1888,6 +1888,12 @@ int __init register_tracer(struct tracer *type) return -1; }

• if (security_locked_down(LOCKDOWN_TRACEFS)) {

• pr_warning("Can not register tracer %s due to lockdown\n",
  

• 	   type->name);
  

• return -EPERM;
  

• }
• mutex_lock(&trace_types_lock);

tracing_selftest_running = true; @@ -8789,6 +8795,11 @@ struct dentry *tracing_init_dentry(void) { struct trace_array *tr = &global_trace;

• if (security_locked_down(LOCKDOWN_TRACEFS)) {

• pr_warning("Tracing disabled due to lockdown\n");
  

• return ERR_PTR(-EPERM);
  

• }
• /* The top level trace array uses NULL as parent */ if (tr->dir) return NULL;

@@ -9231,6 +9242,12 @@ __init static int tracer_alloc_buffers(void) int ring_buf_size; int ret = -ENOMEM;

• if (security_locked_down(LOCKDOWN_TRACEFS)) {

• pr_warning("Tracing disabled due to lockdown\n");
  

• return -EPERM;
  

• }
• /*
  • Make sure we don't accidently add more trace options
  • than we have bits for.

-- 2.24.0