Initial commit of nss-localuserguppy_6.99.4guppy_6.99.3guppy_6.99.2guppy_6.99.1guppy/6.99.4guppy/6.99.3guppy/6.99.2guppy/6.99.16.99.46.99.36.99.26.99.1

`nss-localuser` is a plugin for the GNU Name Service Switch (NSS)
functionality of the GNU C Library (`glibc`) providing host name
resolution for *"localuser"* family of virtual hostnames.

The delivered NSS service defines one virtual host of name `localuser`
that resolves to an IP address of the localhost loopback that integrates
user ID.

Change-Id: I2a33dc23518ce3f4581f5c37df9476dbbc58f262
Signed-off-by: José Bollo <jose.bollo@iot.bzh>

1 files changed, 301 insertions, 0 deletions

diff --git a/localuser.c b/localuser.c
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+++ b/localuser.c
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+/*
+ * Copyright 2018 IoT.bzh <jose.bollo@iot.bzh>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+/*
+ * localuser.c
+ * -----------
+ *  This source file provides NSS (Name Service Switch -see [1]-) facilities
+ *  for defining a virtual host of name localuser that resolves to an address
+ *  of the localhost that integrate user ID.
+ *
+ *  The name "localuser" is resolved to the IPv4 address 127.x.y.z
+ *  where x.y.z resolves to the current user UID = 65536*(x - 128) + 256*y + z
+ *
+ *  The name "localuser-UID" is resolved to the address 127.x.y.z
+ *  where UID = 65536*(x - 128) + 256*y + z
+ *
+ *  Allowed UID are from 0 to 4194303 included.
+ *
+ *  Examples:
+ *    localuser      => 127.128.0.0   (when UID = 0)
+ *    localuser      => 127.128.3.233 (when UID = 1001)
+ *    localuser-1024 => 127.128.4.0   (always)
+ *
+ *  This module provides the reverse resolution.
+ *
+ *  This module provides a value for IPv6: it translate to a IPv4-mapped IPv6 address
+ *  because IPv6 lakes of loopback range.
+ *
+ *  Example: localuser-1024 => ::ffff:127.128.4.0
+ *
+ * links
+ * -----
+ *  [1] https://www.gnu.org/software/libc/manual/html_node/Name-Service-Switch.html
+ */
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <netdb.h>
+#include <nss.h>
+
+/* string for "localuser" */
+static const char localuser[] = "localuser";
+static const char separator = '-';
+
+/* defines the length of adresses */
+static const int lenip4 = 4;
+static const int lenip6 = 16;
+
+/* masks for IPv4 adresses */
+static const uint32_t prefix_mask  = 0xffc00000u; /* 255.192.0.0 */
+static const uint32_t prefix_value = 0x7f800000u; /* 127.128.0.0 */
+static const uint32_t locusr_mask  = 0x003fffffu; /* 0.63.255.255 */
+
+/* return the IPv4 localuser address for 'uid' */
+static uint32_t get_localuser(uint32_t uid)
+{
+	uint32_t adr = (uint32_t)(prefix_value | (locusr_mask & uid));
+	return htonl(adr);
+}
+
+/* is 'ip' a localuser IPv4 address ? */
+static int is_localuser(uint32_t ip)
+{
+	return prefix_value == (ntohl(ip) & prefix_mask);
+}
+
+/* return the user of the localuser IPv4 'ip' */
+static uint32_t uid_of_localuser(uint32_t ip)
+{
+	return (ntohl(ip) & locusr_mask);
+}
+
+/* put in 'buffer' the IPv4 localuser address for 'uid' */
+static void getIPv4(uint32_t *buffer, uint32_t uid)
+{
+	buffer[0] = get_localuser(uid);
+}
+
+/* is 'buffer' pointing a localuser IPv4 address ? */
+static int isIPv4(const uint32_t *buffer)
+{
+	return is_localuser(buffer[0]);
+}
+
+/* return the user of the localuser IPv4 pointed by 'buffer' */
+static uint32_t uidIPv4(const uint32_t *buffer)
+{
+	return uid_of_localuser(buffer[0]);
+}
+
+/* put in 'buffer' the IPv6 localuser address for 'uid' */
+static void getIPv6(uint32_t *buffer, uint32_t uid)
+{
+	buffer[0] = 0;
+	buffer[1] = 0;
+	buffer[2] = htonl(0xffff);
+	buffer[3] = get_localuser(uid);
+}
+
+/* is 'buffer' pointing a localuser IPv6 address ? */
+static int isIPv6(const uint32_t *buffer)
+{
+	return buffer[0] == 0 && buffer[1] == 0
+	    && buffer[2] == htonl(0xffff) && is_localuser(buffer[3]);
+}
+
+/* return the user of the localuser IPv6 pointed by 'buffer' */
+static uint32_t uidIPv6(const uint32_t *buffer)
+{
+	return uid_of_localuser(buffer[3]);
+}
+
+/* fill the output entry */
+static enum nss_status fillent(
+	const char *name,
+	int af,
+	struct hostent *result,
+	char *buffer,
+	size_t buflen,
+	int *errnop,
+	int *h_errnop,
+	uint32_t uid)
+{
+	int alen = 1 + (int)strlen(name);
+	int len = af == AF_INET ? lenip4 : lenip6;
+
+	/* check the family */
+	if (af != AF_INET && af != AF_INET6) {
+		*errnop = EINVAL;
+		*h_errnop = NO_RECOVERY;
+		return NSS_STATUS_UNAVAIL;
+	}
+
+	/* fill aliases and addr_list */
+	if (buflen < 2 * sizeof result->h_aliases[0] + alen + len) {
+		*errnop = ERANGE;
+		*h_errnop = NO_RECOVERY;
+		return NSS_STATUS_TRYAGAIN;
+	}
+
+	/* fill the result */
+	result->h_addrtype = af;
+	result->h_length = len;
+	result->h_addr_list = (char**)buffer;
+	result->h_addr_list[0] = (char*)&result->h_addr_list[2];
+	result->h_name = &result->h_addr_list[0][len];
+	result->h_aliases = &result->h_addr_list[1];
+	result->h_addr_list[1] = NULL;
+	(af == AF_INET ? getIPv4 : getIPv6)((uint32_t*)result->h_addr_list[0], uid);
+	memcpy(result->h_name, name, alen);
+
+	return NSS_STATUS_SUCCESS;
+}
+
+/* gethostbyname2 implementation for NSS */
+enum nss_status _nss_localuser_gethostbyname2_r(
+	const char *name,
+	int af,
+	struct hostent *result,
+	char *buffer,
+	size_t buflen,
+	int *errnop,
+	int *h_errnop)
+{
+	int valid;
+	uint32_t uid;
+	const char *i;
+	char c;
+
+	/* test the name */
+	valid = !strncmp(name, localuser, sizeof localuser - 1);
+	if (valid) {
+		c = name[sizeof localuser - 1];
+		if (!c) {
+			/* terminated string: use current UID */
+			uid = (uint32_t)getuid();
+		} else if (c != separator) {
+			valid = 0;
+		} else {
+			/* has a uid specification */
+			i = &name[sizeof localuser];
+			c = *i;
+			valid = '0' <= c && c <= '9';
+			if (valid) {
+				uid = (uint32_t)(c - '0');
+				while ((c = *++i) && (valid = '0' <= c && c <= '9')) {
+					uid = (uid << 3) + (uid << 1) + (uint32_t)(c - '0');
+				}
+				if (valid)
+					valid = uid == (uid & locusr_mask);
+			}
+		}
+	}
+	if (!valid) {
+		*h_errnop = HOST_NOT_FOUND;
+		return NSS_STATUS_NOTFOUND;
+	}
+
+	/* set default family to IPv4 */
+	if (af == AF_UNSPEC)
+		af = AF_INET;
+
+	/* fill the result */
+	return fillent(name, af, result, buffer, buflen, errnop, h_errnop, uid);
+}
+
+/* use gethostbyname2 implementation */
+enum nss_status _nss_localuser_gethostbyname_r(
+	const char *name,
+	struct hostent *result,
+	char *buffer,
+	size_t buflen,
+	int *errnop,
+	int *h_errnop)
+{
+	return _nss_localuser_gethostbyname2_r(name,
+					       AF_UNSPEC,
+					       result,
+					       buffer, buflen, errnop,
+					       h_errnop);
+}
+
+/* get the name of the address */
+enum nss_status _nss_localuser_gethostbyaddr_r(
+	const void *addr,
+	int len,
+	int af,
+	struct hostent *result,
+	char *buffer,
+	size_t buflen,
+	int *errnop,
+	int *h_errnop)
+{
+	char c, name[40 + sizeof localuser];
+	uint32_t uid, x;
+	int l, u;
+
+	/* set default family */
+	if (af == AF_UNSPEC) {
+		if (len == lenip4)
+			af = AF_INET;
+		else if (len == lenip6)
+			af = AF_INET6;
+	}
+
+	/* check whether the IP comforms to localuser */
+	if (af == AF_INET && len == lenip4 && isIPv4((const uint32_t*)addr)) {
+		/* yes, it's a IPv4, get the uid */
+		uid = uidIPv4((const uint32_t*)addr);
+	} else if (af == AF_INET6 && len == lenip6 && isIPv6((const uint32_t*)addr)) {
+		/* yes, it's a IPv6, get the uid */
+		uid = uidIPv6((const uint32_t*)addr);
+	} else {
+		/* no */
+		/* fail */
+		*errnop = EINVAL;
+		*h_errnop = NO_RECOVERY;
+		return NSS_STATUS_NOTFOUND;
+	}
+
+	/* build the name */
+	memcpy(name, localuser, sizeof localuser - 1);
+	if (uid == (uint32_t)getuid())
+		name[sizeof localuser - 1] = 0;
+	else {
+		x = uid;
+		name[sizeof localuser - 1] = separator;
+		l = u = (int)sizeof localuser;
+		do {
+			name[u++] = (char)('0' + x % 10);
+			x /= 10;
+		} while(x);
+		name[u--] = 0;
+		while (u > l) {
+			c = name[u];
+			name[u--] = name[l];
+			name[l++] = c;
+		}
+	}
+	/* fill the result */
+	return fillent(name, af, result, buffer, buflen, errnop, h_errnop, uid);
+}