[PATCH 5.4 37/40] ring-buffer: Fix memory leak of free page

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

commit 17d801758157bec93f26faaf5ff1a8b9a552d67a upstream.

Reading the ring buffer does a swap of a sub-buffer within the ring buffer
with a empty sub-buffer. This allows the reader to have full access to the
content of the sub-buffer that was swapped out without having to worry
about contention with the writer.

The readers call ring_buffer_alloc_read_page() to allocate a page that
will be used to swap with the ring buffer. When the code is finished with
the reader page, it calls ring_buffer_free_read_page(). Instead of freeing
the page, it stores it as a spare. Then next call to
ring_buffer_alloc_read_page() will return this spare instead of calling
into the memory management system to allocate a new page.

Unfortunately, on freeing of the ring buffer, this spare page is not
freed, and causes a memory leak.

Link: https://lore.kernel.org/linux-trace-kernel/20231210221250.7b9cc83c@rorschach.local.home

Cc: stable@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: 73a757e63114d ("ring-buffer: Return reader page back into existing ring buffer")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/trace/ring_buffer.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1414,6 +1414,8 @@ static void rb_free_cpu_buffer(struct ri
 		free_buffer_page(bpage);
 	}
 
+	free_page((unsigned long)cpu_buffer->free_page);
+
 	kfree(cpu_buffer);
 }