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

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Date:	Mon, 23 Mar 2015 08:35:07 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Alexei Starovoitov <ast@...mgrid.com>
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


* 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?

> +			puts(buf);
> +		}
> +	}


Thanks,

	Ingo
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