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SubjectRe: [PATCH V2 1/2] tracing/probes: Fix a warning message to show correct maximum length
On Fri, 10 Feb 2017 22:21:55 +0900
Masami Hiramatsu <mhiramat@kernel.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=@jiffies_64' > kprobe_events

works just fine. My tests work with 4095 characters. Before and after
my patch.

-- Steve

>
> 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.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.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;
> }

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