[PATCH 6.19 836/844] tracing: ring-buffer: Fix to check event length before using

[Sasha Levin]

From: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>

[ Upstream commit 912b0ee248c529a4f45d1e7f568dc1adddbf2a4a ]

Check the event length before adding it for accessing next index in
rb_read_data_buffer(). Since this function is used for validating
possibly broken ring buffers, the length of the event could be broken.
In that case, the new event (e + len) can point a wrong address.
To avoid invalid memory access at boot, check whether the length of
each event is in the possible range before using it.

Cc: stable@xxxxxxxxxxxxxxx
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Fixes: 5f3b6e839f3c ("ring-buffer: Validate boot range memory events")
Link: https://patch.msgid.link/177123421541.142205.9414352170164678966.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/trace/ring_buffer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ad08430347b06..2f44063c666f2 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1848,6 +1848,7 @@ static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu
 	struct ring_buffer_event *event;
 	u64 ts, delta;
 	int events = 0;
+	int len;
 	int e;
 
 	*delta_ptr = 0;
@@ -1855,9 +1856,12 @@ static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu
 
 	ts = dpage->time_stamp;
 
-	for (e = 0; e < tail; e += rb_event_length(event)) {
+	for (e = 0; e < tail; e += len) {
 
 		event = (struct ring_buffer_event *)(dpage->data + e);
+		len = rb_event_length(event);
+		if (len <= 0 || len > tail - e)
+			return -1;
 
 		switch (event->type_len) {
 
-- 
2.51.0