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Always resolve localhost to loopback address

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This always resolves "localhost" to a loopback address which
has security benefits such as preventing a malicious dns server
redirecting local connections and allows software to assume
it is a secure hostname.

This is being adopted by web browsers:

- https://w3c.github.io/webappsec-secure-contexts/
- https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/RC9dSw-O3fE/E3_0XaT0BAAJ
- 8da2a80724
- https://bugs.webkit.org/show_bug.cgi?id=171934
- https://tools.ietf.org/html/draft-west-let-localhost-be-localhost-06
This commit is contained in:
Patrick Griffis
2019-02-05 08:53:44 -05:00
committed by Philip Withnall
parent 01acb8907f
commit ea99872e45
3 changed files with 257 additions and 5 deletions
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67
gio/gresolver.c
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@@ -296,15 +296,50 @@ remove_duplicates (GList *addrs)
}
}
static gboolean
hostname_is_localhost (const char *hostname)
{
size_t len = strlen (hostname);
const char *p;
/* Match "localhost", "localhost.", "*.localhost" and "*.localhost." */
if (len < strlen ("localhost"))
return FALSE;
if (hostname[len - 1] == '.')
len--;
/* Scan backwards in @hostname to find the right-most dot (excluding the final dot, if it exists, as it was chopped off above).
* We can’t use strrchr() because because we need to operate with string lengths.
* End with @p pointing to the character after the right-most dot. */
p = hostname + len - 1;
while (p >= hostname)
{
if (*p == '.')
{
p++;
break;
}
else if (p == hostname)
break;
p--;
}
len -= p - hostname;
return g_ascii_strncasecmp (p, "localhost", MAX (len, strlen ("localhost"))) == 0;
}
/* Note that this does not follow the "FALSE means @error is set"
* convention. The return value tells the caller whether it should
* return @addrs and @error to the caller right away, or if it should
* continue and trying to resolve the name as a hostname.
*/
static gboolean
handle_ip_address (const char *hostname,
GList **addrs,
GError **error)
handle_ip_address_or_localhost (const char *hostname,
GList **addrs,
GResolverNameLookupFlags flags,
GError **error)
{
GInetAddress *addr;
@@ -355,6 +390,28 @@ handle_ip_address (const char *hostname,
return TRUE;
}
/* Always resolve localhost to a loopback address so it can be reliably considered secure.
This behavior is being adopted by browsers:
- https://w3c.github.io/webappsec-secure-contexts/
- https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/RC9dSw-O3fE/E3_0XaT0BAAJ
- https://chromium.googlesource.com/chromium/src.git/+/8da2a80724a9b896890602ff77ef2216cb951399
- https://bugs.webkit.org/show_bug.cgi?id=171934
- https://tools.ietf.org/html/draft-west-let-localhost-be-localhost-06
*/
if (hostname_is_localhost (hostname))
{
if (flags & G_RESOLVER_NAME_LOOKUP_FLAGS_IPV6_ONLY)
*addrs = g_list_append (*addrs, g_inet_address_new_loopback (G_SOCKET_FAMILY_IPV6));
if (flags & G_RESOLVER_NAME_LOOKUP_FLAGS_IPV4_ONLY)
*addrs = g_list_append (*addrs, g_inet_address_new_loopback (G_SOCKET_FAMILY_IPV4));
if (*addrs == NULL)
{
*addrs = g_list_append (*addrs, g_inet_address_new_loopback (G_SOCKET_FAMILY_IPV6));
*addrs = g_list_append (*addrs, g_inet_address_new_loopback (G_SOCKET_FAMILY_IPV4));
}
return TRUE;
}
return FALSE;
}
@@ -374,7 +431,7 @@ lookup_by_name_real (GResolver *resolver,
g_return_val_if_fail (error == NULL || *error == NULL, NULL);
/* Check if @hostname is just an IP address */
if (handle_ip_address (hostname, &addrs, error))
if (handle_ip_address_or_localhost (hostname, &addrs, flags, error))
return addrs;
if (g_hostname_is_non_ascii (hostname))
@@ -513,7 +570,7 @@ lookup_by_name_async_real (GResolver *resolver,
g_return_if_fail (!(flags & G_RESOLVER_NAME_LOOKUP_FLAGS_IPV4_ONLY && flags & G_RESOLVER_NAME_LOOKUP_FLAGS_IPV6_ONLY));
/* Check if @hostname is just an IP address */
if (handle_ip_address (hostname, &addrs, &error))
if (handle_ip_address_or_localhost (hostname, &addrs, flags, &error))
{
GTask *task;