From: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
Date: Fri, 18 Mar 2016 19:46:48 +0000 (-0400)
Subject: tracing: Fix crash from reading trace_pipe with sendfile
X-Git-Tag: v3.2.80~65
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1719bf67d6c52a9bc84ddf24a3e85d5f69fe3f90;p=pandora-kernel.git

tracing: Fix crash from reading trace_pipe with sendfile

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@rab.in

Reported-by: Rabin Vincent <rabin.vincent@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 0c348a63be49..f4b93a207026 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3565,7 +3565,10 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 
 	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;