1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  * All rights reserved.
4  *
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9  *    notice, this list of conditions and the following disclaimer.
10  *  * Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in
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13  *    distribution.
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15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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19  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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27  */
28 
29 #include <ifaddrs.h>
30 
31 #include <errno.h>
32 #include <linux/if_packet.h>
33 #include <net/if.h>
34 #include <netinet/in.h>
35 #include <stdint.h>
36 #include <stdio.h>
37 #include <stdlib.h>
38 #include <string.h>
39 #include <unistd.h>
40 
41 #include "private/ErrnoRestorer.h"
42 
43 #include "bionic_netlink.h"
44 
45 // The public ifaddrs struct is full of pointers. Rather than track several
46 // different allocations, we use a maximally-sized structure with the public
47 // part at offset 0, and pointers into its hidden tail.
48 struct ifaddrs_storage {
49   // Must come first, so that `ifaddrs_storage` is-a `ifaddrs`.
50   ifaddrs ifa;
51 
52   // The interface index, so we can match RTM_NEWADDR messages with
53   // earlier RTM_NEWLINK messages (to copy the interface flags).
54   int interface_index;
55 
56   // Storage for the pointers in `ifa`.
57   sockaddr_storage addr;
58   sockaddr_storage netmask;
59   sockaddr_storage ifa_ifu;
60   char name[IFNAMSIZ + 1];
61 
ifaddrs_storageifaddrs_storage62   ifaddrs_storage(ifaddrs** list) {
63     memset(this, 0, sizeof(*this));
64 
65     // push_front onto `list`.
66     ifa.ifa_next = *list;
67     *list = reinterpret_cast<ifaddrs*>(this);
68   }
69 
SetAddressifaddrs_storage70   void SetAddress(int family, const void* data, size_t byteCount) {
71     // The kernel currently uses the order IFA_ADDRESS, IFA_LOCAL, IFA_BROADCAST
72     // in inet_fill_ifaddr, but let's not assume that will always be true...
73     if (ifa.ifa_addr == nullptr) {
74       // This is an IFA_ADDRESS and haven't seen an IFA_LOCAL yet, so assume this is the
75       // local address. SetLocalAddress will fix things if we later see an IFA_LOCAL.
76       ifa.ifa_addr = CopyAddress(family, data, byteCount, &addr);
77     } else {
78       // We already saw an IFA_LOCAL, which implies this is a destination address.
79       ifa.ifa_dstaddr = CopyAddress(family, data, byteCount, &ifa_ifu);
80     }
81   }
82 
SetBroadcastAddressifaddrs_storage83   void SetBroadcastAddress(int family, const void* data, size_t byteCount) {
84     // ifa_broadaddr and ifa_dstaddr overlap in a union. Unfortunately, it's possible
85     // to have an interface with both. Keeping the last thing the kernel gives us seems
86     // to be glibc 2.19's behavior too, so our choice is being source compatible with
87     // badly-written code that assumes ifa_broadaddr and ifa_dstaddr are interchangeable
88     // or supporting interfaces with both addresses configured. My assumption is that
89     // bad code is more common than weird network interfaces...
90     ifa.ifa_broadaddr = CopyAddress(family, data, byteCount, &ifa_ifu);
91   }
92 
SetLocalAddressifaddrs_storage93   void SetLocalAddress(int family, const void* data, size_t byteCount) {
94     // The kernel source says "for point-to-point IFA_ADDRESS is DESTINATION address,
95     // local address is supplied in IFA_LOCAL attribute".
96     //   -- http://lxr.free-electrons.com/source/include/uapi/linux/if_addr.h#L17
97 
98     // So copy any existing IFA_ADDRESS into ifa_dstaddr...
99     if (ifa.ifa_addr != nullptr) {
100       ifa.ifa_dstaddr = reinterpret_cast<sockaddr*>(memcpy(&ifa_ifu, &addr, sizeof(addr)));
101     }
102     // ...and then put this IFA_LOCAL into ifa_addr.
103     ifa.ifa_addr = CopyAddress(family, data, byteCount, &addr);
104   }
105 
106   // Netlink gives us the prefix length as a bit count. We need to turn
107   // that into a BSD-compatible netmask represented by a sockaddr*.
SetNetmaskifaddrs_storage108   void SetNetmask(int family, size_t prefix_length) {
109     // ...and work out the netmask from the prefix length.
110     netmask.ss_family = family;
111     uint8_t* dst = SockaddrBytes(family, &netmask);
112     memset(dst, 0xff, prefix_length / 8);
113     if ((prefix_length % 8) != 0) {
114       dst[prefix_length/8] = (0xff << (8 - (prefix_length % 8)));
115     }
116     ifa.ifa_netmask = reinterpret_cast<sockaddr*>(&netmask);
117   }
118 
SetPacketAttributesifaddrs_storage119   void SetPacketAttributes(int ifindex, unsigned short hatype, unsigned char halen) {
120     sockaddr_ll* sll = reinterpret_cast<sockaddr_ll*>(&addr);
121     sll->sll_ifindex = ifindex;
122     sll->sll_hatype = hatype;
123     sll->sll_halen = halen;
124   }
125 
126  private:
CopyAddressifaddrs_storage127   sockaddr* CopyAddress(int family, const void* data, size_t byteCount, sockaddr_storage* ss) {
128     // Netlink gives us the address family in the header, and the
129     // sockaddr_in or sockaddr_in6 bytes as the payload. We need to
130     // stitch the two bits together into the sockaddr that's part of
131     // our portable interface.
132     ss->ss_family = family;
133     memcpy(SockaddrBytes(family, ss), data, byteCount);
134 
135     // For IPv6 we might also have to set the scope id.
136     if (family == AF_INET6 && (IN6_IS_ADDR_LINKLOCAL(data) || IN6_IS_ADDR_MC_LINKLOCAL(data))) {
137       reinterpret_cast<sockaddr_in6*>(ss)->sin6_scope_id = interface_index;
138     }
139 
140     return reinterpret_cast<sockaddr*>(ss);
141   }
142 
143   // Returns a pointer to the first byte in the address data (which is
144   // stored in network byte order).
SockaddrBytesifaddrs_storage145   uint8_t* SockaddrBytes(int family, sockaddr_storage* ss) {
146     if (family == AF_INET) {
147       sockaddr_in* ss4 = reinterpret_cast<sockaddr_in*>(ss);
148       return reinterpret_cast<uint8_t*>(&ss4->sin_addr);
149     } else if (family == AF_INET6) {
150       sockaddr_in6* ss6 = reinterpret_cast<sockaddr_in6*>(ss);
151       return reinterpret_cast<uint8_t*>(&ss6->sin6_addr);
152     } else if (family == AF_PACKET) {
153       sockaddr_ll* sll = reinterpret_cast<sockaddr_ll*>(ss);
154       return reinterpret_cast<uint8_t*>(&sll->sll_addr);
155     }
156     return nullptr;
157   }
158 };
159 
__getifaddrs_callback(void * context,nlmsghdr * hdr)160 static void __getifaddrs_callback(void* context, nlmsghdr* hdr) {
161   ifaddrs** out = reinterpret_cast<ifaddrs**>(context);
162 
163   if (hdr->nlmsg_type == RTM_NEWLINK) {
164     ifinfomsg* ifi = reinterpret_cast<ifinfomsg*>(NLMSG_DATA(hdr));
165 
166     // Create a new ifaddr entry, and set the interface index and flags.
167     ifaddrs_storage* new_addr = new ifaddrs_storage(out);
168     new_addr->interface_index = ifi->ifi_index;
169     new_addr->ifa.ifa_flags = ifi->ifi_flags;
170 
171     // Go through the various bits of information and find the name.
172     rtattr* rta = IFLA_RTA(ifi);
173     size_t rta_len = IFLA_PAYLOAD(hdr);
174     while (RTA_OK(rta, rta_len)) {
175       if (rta->rta_type == IFLA_ADDRESS) {
176           if (RTA_PAYLOAD(rta) < sizeof(new_addr->addr)) {
177             new_addr->SetAddress(AF_PACKET, RTA_DATA(rta), RTA_PAYLOAD(rta));
178             new_addr->SetPacketAttributes(ifi->ifi_index, ifi->ifi_type, RTA_PAYLOAD(rta));
179           }
180       } else if (rta->rta_type == IFLA_BROADCAST) {
181           if (RTA_PAYLOAD(rta) < sizeof(new_addr->ifa_ifu)) {
182             new_addr->SetBroadcastAddress(AF_PACKET, RTA_DATA(rta), RTA_PAYLOAD(rta));
183             new_addr->SetPacketAttributes(ifi->ifi_index, ifi->ifi_type, RTA_PAYLOAD(rta));
184           }
185       } else if (rta->rta_type == IFLA_IFNAME) {
186           if (RTA_PAYLOAD(rta) < sizeof(new_addr->name)) {
187             memcpy(new_addr->name, RTA_DATA(rta), RTA_PAYLOAD(rta));
188             new_addr->ifa.ifa_name = new_addr->name;
189           }
190       }
191       rta = RTA_NEXT(rta, rta_len);
192     }
193   } else if (hdr->nlmsg_type == RTM_NEWADDR) {
194     ifaddrmsg* msg = reinterpret_cast<ifaddrmsg*>(NLMSG_DATA(hdr));
195 
196     // We should already know about this from an RTM_NEWLINK message.
197     const ifaddrs_storage* addr = reinterpret_cast<const ifaddrs_storage*>(*out);
198     while (addr != nullptr && addr->interface_index != static_cast<int>(msg->ifa_index)) {
199       addr = reinterpret_cast<const ifaddrs_storage*>(addr->ifa.ifa_next);
200     }
201     // If this is an unknown interface, ignore whatever we're being told about it.
202     if (addr == nullptr) return;
203 
204     // Create a new ifaddr entry and copy what we already know.
205     ifaddrs_storage* new_addr = new ifaddrs_storage(out);
206     // We can just copy the name rather than look for IFA_LABEL.
207     strcpy(new_addr->name, addr->name);
208     new_addr->ifa.ifa_name = new_addr->name;
209     new_addr->ifa.ifa_flags = addr->ifa.ifa_flags;
210     new_addr->interface_index = addr->interface_index;
211 
212     // Go through the various bits of information and find the address
213     // and any broadcast/destination address.
214     rtattr* rta = IFA_RTA(msg);
215     size_t rta_len = IFA_PAYLOAD(hdr);
216     while (RTA_OK(rta, rta_len)) {
217       if (rta->rta_type == IFA_ADDRESS) {
218         if (msg->ifa_family == AF_INET || msg->ifa_family == AF_INET6) {
219           new_addr->SetAddress(msg->ifa_family, RTA_DATA(rta), RTA_PAYLOAD(rta));
220           new_addr->SetNetmask(msg->ifa_family, msg->ifa_prefixlen);
221         }
222       } else if (rta->rta_type == IFA_BROADCAST) {
223         if (msg->ifa_family == AF_INET) {
224           new_addr->SetBroadcastAddress(msg->ifa_family, RTA_DATA(rta), RTA_PAYLOAD(rta));
225         }
226       } else if (rta->rta_type == IFA_LOCAL) {
227         if (msg->ifa_family == AF_INET || msg->ifa_family == AF_INET6) {
228           new_addr->SetLocalAddress(msg->ifa_family, RTA_DATA(rta), RTA_PAYLOAD(rta));
229         }
230       }
231       rta = RTA_NEXT(rta, rta_len);
232     }
233   }
234 }
235 
getifaddrs(ifaddrs ** out)236 int getifaddrs(ifaddrs** out) {
237   // We construct the result directly into `out`, so terminate the list.
238   *out = nullptr;
239 
240   // Open the netlink socket and ask for all the links and addresses.
241   NetlinkConnection nc;
242   bool okay = nc.SendRequest(RTM_GETLINK) && nc.ReadResponses(__getifaddrs_callback, out) &&
243               nc.SendRequest(RTM_GETADDR) && nc.ReadResponses(__getifaddrs_callback, out);
244   if (!okay) {
245     freeifaddrs(*out);
246     // Ensure that callers crash if they forget to check for success.
247     *out = nullptr;
248     return -1;
249   }
250 
251   return 0;
252 }
253 
freeifaddrs(ifaddrs * list)254 void freeifaddrs(ifaddrs* list) {
255   while (list != nullptr) {
256     ifaddrs* current = list;
257     list = list->ifa_next;
258     free(current);
259   }
260 }
261