netdev - Re: [PATCH v9 tip 6/9] samples: bpf: simple non-portable kprobe filter example

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Date:	Mon, 23 Mar 2015 10:32:45 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel@...earbox.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 tip 6/9] samples: bpf: simple non-portable kprobe filter
 example

On 3/23/15 12:35 AM, Ingo Molnar wrote:
>
> * Alexei Starovoitov <ast@...mgrid.com> wrote:
>
>> +void read_trace_pipe(void)
>> +{
>> +	int trace_fd;
>> +
>> +	trace_fd = open(DEBUGFS "trace_pipe", O_RDONLY, 0);
>> +	if (trace_fd < 0)
>> +		return;
>> +
>> +	while (1) {
>> +		static char buf[4096];
>> +		ssize_t sz;
>> +
>> +		sz = read(trace_fd, buf, sizeof(buf));
>
> read() will return -1 on failure ...
>
>> +		if (sz) {
>
> ... this test passes ...
>
>> +			buf[sz] = 0;
>
> ... and here we smash the stack?

good point. If it was normal file, for sure it's a bug, but trace_pipe
is a pseudo file and I think read cannot return -1. Regardless, it makes
sense to fix it. Will do. Do you mind I address it as follow up patch?
Or if the rest is ok, can you change the condition to sz>0 while
applying? I can respin the whole thing too, if you like.
Thanks!
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