netdev - Re: strange behaviour in ping when specifying timeout in msec

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Date:	Mon, 10 Aug 2009 14:09:43 -0500
From:	Brent Cook <bcook@...intsys.com>
To:	Michele BOLOGNA <michele.bologna@...il.com>
Cc:	yoshfuji@...ux-ipv6.org, netdev@...r.kernel.org
Subject: Re: strange behaviour in ping when specifying timeout in msec

On Wednesday 05 August 2009 06:27:14 pm Michele BOLOGNA wrote:
> Dear Mr. Yoshifuji,
> I recently noticed a strange behaviour in ping from iputils.
>
> First of all some information:
> mbologna@...tune:~$ ping -V
> ping utility, iputils-sss20071127
>
> Now, I want to specify a timeout and after it expires I would like
> that ping exits, regardless of the packets received, so I use the -W
> option:
>
>       -W timeout
>               Time to wait for a response, in seconds. The option affects
> only timeout in absense of any responses, otherwise  ping  waits  for two
> RTTs.

If you check out the source to ping, you will see that the results of non-
integer arguments to -W is undefined, since atoi cannot detect errors. In your 
case, its probably being interpreted as 0. You can enter almost any value for 
-W without it showing an error, e.g. 'cat' or 'dog'.

    case 'W':
        lingertime = atoi(optarg);
        if (lingertime < 0 || lingertime > INT_MAX/1000000) {
            fprintf(stderr, "ping: bad linger time.\n");
            exit(2);
        }
        lingertime *= 1000;
        break;

Your best bet is perhaps to modify ping to parse time using strtof perhaps.

 - Brent
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