[PATCH 4.4 165/210] tracing: Fix crash from reading trace_pipe with sendfile

From: Greg Kroah-Hartman
Date: Sun Apr 10 2016 - 15:13:35 EST


4.4-stable review patch. If anyone has any objections, please let me know.

------------------

From: Steven Rostedt (Red Hat) <rostedt@xxxxxxxxxxx>

commit a29054d9478d0435ab01b7544da4f674ab13f533 upstream.

If tracing contains data and the trace_pipe file is read with sendfile(),
then it can trigger a NULL pointer dereference and various BUG_ON within the
VM code.

There's a patch to fix this in the splice_to_pipe() code, but it's also a
good idea to not let that happen from trace_pipe either.

Link: http://lkml.kernel.org/r/1457641146-9068-1-git-send-email-rabin@xxxxxx

Reported-by: Rabin Vincent <rabin.vincent@xxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
kernel/trace/trace.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4949,7 +4949,10 @@ static ssize_t tracing_splice_read_pipe(

spd.nr_pages = i;

- ret = splice_to_pipe(pipe, &spd);
+ if (i)
+ ret = splice_to_pipe(pipe, &spd);
+ else
+ ret = 0;
out:
splice_shrink_spd(&spd);
return ret;