[PATCH] ring-buffer: Do not let subbuf be bigger than write mask

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The data on the subbuffer is measured by a write variable that also
contains status flags. The counter is just 20 bits in length. If the
subbuffer is bigger than then counter, it will fail.

Make sure that the subbuffer can not be set to greater than the counter
that keeps track of the data on the subbuffer.

Fixes: 2808e31ec12e5 ("ring-buffer: Add interface for configuring trace sub buffer size")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index aa54266f5e1f..3852f3b001cc 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5878,6 +5878,10 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 	if (psize <= BUF_PAGE_HDR_SIZE)
 		return -EINVAL;
 
+	/* Size of a subbuf cannot be greater than the write counter */
+	if (psize > RB_WRITE_MASK + 1)
+		return -EINVAL;
+
 	old_order = buffer->subbuf_order;
 	old_size = buffer->subbuf_size;
 
-- 
2.43.0