[PATCH 3.19.y-ckt 107/170] tracing: Fix crash from reading trace_pipe with sendfile

From: Kamal Mostafa
Date: Fri Apr 01 2016 - 21:14:31 EST


3.19.8-ckt18 -stable review patch. If anyone has any objections, please let me know.

---8<------------------------------------------------------------

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: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
kernel/trace/trace.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 361a827..bd3e6b1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4705,7 +4705,10 @@ 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;
--
2.7.4