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

[ 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@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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index fdb3153bbf487741d5577e5889ab1972ee6c31d9..54d70bd0a3cb9593f53ba8f95f71f28e846000e9 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1813,6 +1813,7 @@ 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;
@@ -1820,9 +1821,12 @@ 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) {