PHP: gethostbyname bug

Question

I am using gethostbyname() to get the ip address of domains in an application.

In some cases invalid addresses like '50.9.49' are checked also.

echo gethostbyname('50.9.49'); // returns 50.9.0.49

In this cases gethostbyname should return false or the unmodified invalid ip address. however the functions returns the modified IP address 50.9.0.49.

Looks like a bug in php. The quick fix seems to be to check for invalid numerical addresses before, are there any other suggestions?

I think PHP is not the only place where this happens. It also happens when using `ping 50.9.49` in Windows. I get the response: `Pinging 50.9.0.49 with 32 bytes of data...` — Simon Forsberg, May 16 '12 at 17:17
Its some kind assuming `0`s in the middle to make it 4 byte long address. — Shiplu Mokaddim, May 16 '12 at 17:24
@harald: Indeed, for the ones who are too lazy to type an extra zero. — Shubham, May 16 '12 at 17:24
I believe we have discovered an `undocumented feature` here. — Simon Forsberg, May 16 '12 at 17:34

score 7 · Accepted Answer · answered May 16 '12 at 17:38

PHP's gethostbyname actually uses the results of the underlying OS's gethostbyname, e.g., from Linux's netdb.h or Windows' Winsock2.h. It's those functions that actually produce the return value, not PHP.

/* {{{ php_gethostbyname */
static char *php_gethostbyname(char *name)
{
    struct hostent *hp;
    struct in_addr in;

    hp = gethostbyname(name);

    if (!hp || !*(hp->h_addr_list)) {
        return estrdup(name);
    }

    memcpy(&in.s_addr, *(hp->h_addr_list), sizeof(in.s_addr));

    return estrdup(inet_ntoa(in));
}
/* }}} */

score 3 · Answer 2 · answered May 16 '12 at 17:39

3

It seems like this is an undocumented feature for how IPs works. As mentioned in the comments for your question, ping 50.9.49 in Windows actually pings 50.9.0.49. If you enter an adress as a.b.d, it automatically inserts a zero as c: a.b.0.d. If you just enter a.d, two zeroes are inserted: a.0.0.d.

This has been tested with both Windows 7 and Debian Linux.

answered May 16 '12 at 17:39

Simon Forsberg

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It actually goes further than that -- the third "octet" is treated as a 16-bit value. Pinging `1.2.772` gets you `1.2.3.4`, since 772 is 0x0304. Indeed, you can `ping 16909060` (0x01020304) to get the same result! – May 16 '12 at 17:42
1

`ping 50` gets you `0.0.0.50`. – Marcus Adams May 16 '12 at 17:50

PHP: gethostbyname bug

2 Answers2

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