[PATCH 7.1 207/271] ring-buffer: Prevent subbuf order change when resizing is disabled

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vincent Donnefort <[email protected]>

commit bf98d7b0d5a99991e47e66cee4eb1d3fa514be97 upstream.

Because ring_buffer_subbuf_order_set() frees buffer pages, we can't
allow it when resizing is disabled. A non-consuming reader is at risk of
use-after-free (rb_advance_iter()).

Return -EBUSY on resize_disabled, matching ring_buffer_resize()
behaviour.

Cc: [email protected]
Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page")
Link: https://patch.msgid.link/[email protected]
Reported-by: [email protected]
Signed-off-by: Vincent Donnefort <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 kernel/trace/ring_buffer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -7168,7 +7168,7 @@ int ring_buffer_subbuf_order_set(struct
 
 		cpu_buffer = buffer->buffers[cpu];
 
-		if (cpu_buffer->mapped) {
+		if (atomic_read(&cpu_buffer->resize_disabled)) {
 			err = -EBUSY;
 			goto error;
 		}