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

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.

Link: https://lore.kernel.org/linux-trace-kernel/20240220095112.77e9cb81@gandalf.local.home
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: 2808e31ec12e5 ("ring-buffer: Add interface for configuring trace sub buffer size")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index fd4bfe3ecf014f6b3c83f9a7fa043b7df44dac32..0699027b4f4c92d3a6ed7c62ee64491d7cd89046 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5877,6 +5877,10 @@ 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;