On Wed 2014-11-19 11:00:37, Steven Rostedt wrote: > On Wed, 19 Nov 2014 15:40:05 +0100 > Petr Mladek <pmla...@suse.cz> wrote: > > > > Regardless of overflow or not (or even if trace_seq is full), that if > > > statement will prevent this from doing any buffer overflows. > > > > > > s->seq.len will never be more than s->seq.size after the test against > > > TRACE_MAX_PRINT. So I see no harm here. > > > > Ah, I see. Well, I would feel more comfortable if it uses > > trace_seq_used() or if there is some explanation in a comment. > > But you are right, it is safe as it is. Feel free to leave it. > > > > OK, I added this just for you: > > BTW, using trace_seq_used() would not be good enough because it could > return s->seq.size. Which would overflow the buffer on the > > s->buffer[s->seq.len] = 0;
Great catch! > -- Steve > > From 1922acc9987d23d0b9c1ad28dc3eaafc1cf2d6b7 Mon Sep 17 00:00:00 2001 > From: "Steven Rostedt (Red Hat)" <rost...@goodmis.org> > Date: Wed, 19 Nov 2014 10:56:41 -0500 > Subject: [PATCH] tracing: Add paranoid size check in trace_printk_seq() > > To be really paranoid about writing out of bound data in > trace_printk_seq(), add another check of len compared to size. > > Link: http://lkml.kernel.org/r/20141119144004.gb2...@dhcp128.suse.cz > > Suggested-by: Petr Mladek <pmla...@suse.cz> > Signed-off-by: Steven Rostedt <rost...@goodmis.org> Reviewed-by: Petr Mladek <pmla...@suse.cz> Thanks a lot for the addition. Best Regards, Petr > --- > kernel/trace/trace.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 9023446b2c2b..26facec4625e 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -6656,6 +6656,14 @@ trace_printk_seq(struct trace_seq *s) > if (s->seq.len >= TRACE_MAX_PRINT) > s->seq.len = TRACE_MAX_PRINT; > > + /* > + * More paranoid code. Although the buffer size is set to > + * PAGE_SIZE, and TRACE_MAX_PRINT is 1000, this is just > + * an extra layer of protection. > + */ > + if (WARN_ON_ONCE(s->seq.len >= s->seq.size)) > + s->seq.len = s->seq.size - 1; > + > /* should be zero ended, but we are paranoid. */ > s->buffer[s->seq.len] = 0; > > -- > 1.8.1.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
