tracing: ring-buffer: Fix to check event length before using

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@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index bdc8010d8f482cc3092f145262815e9fee565f55..1e7a34a31851c2c9f97abfc90e292cd8e9190315 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1849,6 +1849,7 @@ 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;
@@ -1856,9 +1857,12 @@ 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) {