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SubjectRe: [PATCH] ftrace: fix task's invalid comm of <...> when big pid
On Wed, 28 Mar 2018 11:35:22 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 28 Mar 2018 20:32:27 +0800
> Wang Yu <yuwang@linux.alibaba.com> wrote:
>
> > when pid is bigger than PID_MAX_DEFAULT, the comm of task
> > is <...>, it is better use pid_max to compare
> >
> > Signed-off-by: Wang Yu <yuwang@linux.alibaba.com>
> > ---
> > kernel/trace/trace.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> > mode change 100644 => 100755 kernel/trace/trace.c
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > old mode 100644
> > new mode 100755
> > index 20a2300..0d4bc7a
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -1976,7 +1976,7 @@ static void __trace_find_cmdline(int pid, char comm[])
> > return;
> > }
> >
> > - if (pid > PID_MAX_DEFAULT) {
> > + if (pid > pid_max) {
>
> Thanks! this probably should go to stable.

I take that back. This patch can cause a buffer overflow access.

If you looked at the line after this check, you would see:

if (pid > PID_MAX_DEFAULT) {
strcpy(comm, "<...>");
return;
}

map = savedcmd->map_pid_to_cmdline[pid];

And if you looked to see what map_pid_to_cmdline is:

struct saved_cmdlines_buffer {
unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];

Your patch will access memory past the end of that array, and cause a
bug.

If you want to support more than PID_MAX_DEFAULT, a lot more needs to
change than this. And a change like this isn't going to go to stable.

What you can do is make that map_pid_to_cmdline array bigger.

-- Steve


>
> -- Steve
>
> > strcpy(comm, "<...>");
> > return;
> > }
>

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