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Message-Id: <20170216001030.bd1ee215ea9d31289e2441ed@kernel.org>
Date: Thu, 16 Feb 2017 00:10:30 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
"H . Peter Anvin" <hpa@...or.com>,
Namhyung Kim <namhyung@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH V2 1/2] tracing/probes: Fix a warning message to show
correct maximum length
On Fri, 10 Feb 2017 11:04:34 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
> On Fri, 10 Feb 2017 22:21:55 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> > Since tracing/*probe_events will accept a probe definition
> > up to 4096 - 2 ('\n' and '\0') bytes, it must show 4094 instead
> > of 4096 in warning message.
>
> Actually, during the testing I found that we don't need the '\n'.
>
> echo -n 'p:irq do_IRQ a=@...fies_64' > kprobe_events
>
> works just fine. My tests work with 4095 characters. Before and after
> my patch.
Yeah, I see. I concider the case that if the writer writes
4095 chars command + '\n' + next command, it will fail, that
is what I pointed out below note.
> >
> > Note that there is one possible case of exceed 4094. If user
> > prepare 4096 bytes null-terminated string and syscall write
> > it with the count == 4095, then it can be accepted. However,
> > if user puts a '\n' after that, it must rejected.
> > So IMHO, the warning message should indicate shorter one,
> > since it is safer.
Thank you,
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> > kernel/trace/trace_probe.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index 2a06f1f..847c1e0 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -678,8 +678,9 @@ ssize_t traceprobe_probes_write(struct file *file, const char __user *buffer,
> > if (done + size < count) {
> > if (buf != kbuf)
> > break;
> > + /* This can accept WRITE_BUFSIZE - 2 ('\n' + '\0') */
> > pr_warn("Line length is too long: Should be less than %d\n",
> > - WRITE_BUFSIZE);
> > + WRITE_BUFSIZE - 2);
> > ret = -EINVAL;
> > goto out;
> > }
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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