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Date: Fri, 19 Jul 2013 17:28:00 +0200
From: Holger Hans Peter Freyther <holger@freyther.de>
To: Nathan Zimmer <nzimmer@sgi.com>
Cc: linux-kernel@vger.kernel.org
Subject: /proc/timer_list and weird behavior with dropbear
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Dear Nathan,

I am currently upgrading a kernel for a TI Davinci DM644x based design
from Linux 3.2 to Linux 3.10.1. I have a funny re-producible issue that
goes away by reverting b3956a896ea57f25cacd74708b8fab611543a81d.

The dropbear sshd will open several files after accepting a connection to
generate some entropy. The "/proc/timer_list" file is part of that[1].
It will open that file and will try to read until the end of the file, but
most of the time this end never comes. According to strace the read on the
fd will always return 2048. I have attached the testcase I am using to
re-produce the issue.

Can this be re-produced by anyone else?

holger



[1] https://secure.ucc.asn.au/hg/dropbear/file/028fa77f952f/random.c#l204


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#include <sys/stat.h>
#include <fcntl.h>

       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/time.h>
       #include <sys/types.h>
       #include <unistd.h>


int main(int argc, char **argv)
{
	fd_set rfds;
	struct timeval tv;
	char buf[2048];

	int fd = open("/proc/timer_list", O_RDONLY, O_NONBLOCK);
	if (fd < 0) {
		perror("Failed to open");
		abort();
	}

	FD_ZERO(&rfds);
	FD_SET(fd, &rfds);


	while (1) {
		tv.tv_sec = 2;
		tv.tv_usec = 0;

		int retval = select(fd + 1, &rfds, NULL, NULL, &tv);
		if (retval == -1)
			perror("select()");
		else if (retval) {
			int ret = read(fd, buf, sizeof(buf));
			if (ret == 0)
				return EXIT_SUCCESS;
		} else {
			printf("TIMEOUT...\n");
		}
	}
}

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