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SubjectRe: [PATCH 2/2] tracing: Use trace_seq_used() and seq_buf_used() instead of len
On Tue, 18 Nov 2014 17:33:54 +0100
Petr Mladek <pmladek@suse.cz> wrote:

> On Mon 2014-11-17 14:12:15, Steven Rostedt wrote:
> >
> > > I don't like the fact that I did a code structure change with this
> > > patch. This patch should be just a simple conversion of len to
> > > seq_buf_used(). I'm going to strip this change out and put it before
> > > this patch.
> >
> >
> > As the seq_buf->len will soon be +1 size when there's an overflow, we
> > must use trace_seq_used() or seq_buf_used() methods to get the real
> > length. This will prevent buffer overflow issues if just the len
> > of the seq_buf descriptor is used to copy memory.
> >
> > Link: http://lkml.kernel.org/r/20141114121911.09ba3d38@gandalf.local.home
> >
> > Reported-by: Petr Mladek <pmladek@suse.cz>
> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> > ---
> > include/linux/trace_seq.h | 20 +++++++++++++++++++-
> > kernel/trace/seq_buf.c | 2 +-
> > kernel/trace/trace.c | 22 +++++++++++-----------
> > kernel/trace/trace_events.c | 9 ++++++---
> > kernel/trace/trace_functions_graph.c | 5 ++++-
> > kernel/trace/trace_seq.c | 2 +-
> > 6 files changed, 42 insertions(+), 18 deletions(-)
>
> [...]
>
>
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -944,10 +944,10 @@ static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
> > {
> > int len;
> >
> > - if (s->seq.len <= s->seq.readpos)
> > + if (trace_seq_used(s) <= s->seq.readpos)
> > return -EBUSY;
> >
> > - len = s->seq.len - s->seq.readpos;
> > + len = trace_seq_used(s) - s->seq.readpos;
> > if (cnt > len)
> > cnt = len;
> > memcpy(buf, s->buffer + s->seq.readpos, cnt);
>
>
> There is one more dangerous usage in trace_printk_seq(). It is on
> three lines there.

You totally confused me. What usage in trace_printk_seq(), and what
three lines?

In this patch, trace_printk_seq() looks like this:

int trace_print_seq(struct seq_file *m, struct trace_seq *s)
{
int ret;

__trace_seq_init(s);

ret = seq_buf_print_seq(m, &s->seq);

/*
* Only reset this buffer if we successfully wrote to the
* seq_file buffer. This lets the caller try again or
* do something else with the contents.
*/
if (!ret)
trace_seq_init(s);

return ret;
}



-- Steve


>
> The rest looks good.
>
> Best Regards,
> Petr



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