[for-linus][PATCH 06/12] ring-buffer: Add checking nr_subbufs to persistent ring buffer validation

[Steven Rostedt <rostedt@kernel.org>]

From: Steven Rostedt <rostedt@goodmis.org>

Sashiko reported that the code was using meta->nr_subbufs without making
sure that it matched the nr_pages + 1 on data that was assuming the two
were the same.

Add a check to the persistent ring buffer validation code to make sure
that the saved nr_subbufs matches what we expect.

Link: https://patch.msgid.link/20260903132728.7fb27d34@gandalf.local.home
Fixes: f5b95f1fa2ef3 ("ring-buffer: Validate the persistent meta data subbuf array")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/all/20260901164836.D962D1F000E9@smtp.kernel.org/
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 84fd4cdd486f..ff0a44aa578d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1856,6 +1856,11 @@ static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu,
 		return false;
 	}
 
+	if (meta->nr_subbufs != nr_pages + 1) {
+		pr_info("Ring buffer boot meta [%d] invalid nr_subbufs\n", cpu);
+		return false;
+	}
+
 	buffers_start = meta->first_buffer;
 	buffers_end = meta->first_buffer + (subbuf_size * meta->nr_subbufs);
 
-- 
2.53.0