[release/7.0][Android] Backport fix NetworkInterface.GetAllNetworkInterfaces (#76565)

* [Android] Fix NetworkInterface.GetAllNetworkInterfaces (#76370)

* Revert "[Android] Port getifaddrs implementation from Xamarin.Android (#71943)"

This reverts commit 1de4a5c.

* Fix allocating memory block for interfaces and addresses on recent Android SDKs

* Detect loopback interface on Android

* Add comment with explanation

* Simplify the changes to be closer to the original code

* Fix build

* Fix typos

Co-authored-by: Alexander Köplinger <[email protected]>

* Improve comment

* Indent using spaces instead of tabs

* Remove check for ifaddrs.h

* Add ANDROID_GETIFADDRS_WORKAROUND

* Update comment

Co-authored-by: Alexander Köplinger <[email protected]>

* [Android] Fix NetworkInterface.GetAllNetworkInterfaces on API 21-23 (#76541)

* Bring back pal_ifaddrs

* Update the header file

Co-authored-by: Alexander Köplinger <[email protected]>

Author: simonrozsival

src/native/libs/System.Native/CMakeLists.txt

@@ -83,7 +83,8 @@ include(${CMAKE_CURRENT_LIST_DIR}/extra_libs.cmake)
 set(NATIVE_LIBS_EXTRA)
 append_extra_system_libs(NATIVE_LIBS_EXTRA)
 
-if (CLR_CMAKE_TARGET_ANDROID)
+if (CLR_CMAKE_TARGET_ANDROID AND NOT HAVE_GETIFADDRS)
+    add_definitions(-DANDROID_GETIFADDRS_WORKAROUND)
     add_compile_options(-Wno-gnu-zero-variadic-macro-arguments)
 
     list (APPEND NATIVE_LIBS_EXTRA -llog)

src/native/libs/System.Native/pal_ifaddrs.c

@@ -708,7 +708,7 @@ static int parse_netlink_reply(struct netlink_session *session, struct ifaddrs *
     return ret;
 }
 
-int getifaddrs(struct ifaddrs **ifap)
+int _netlink_getifaddrs(struct ifaddrs **ifap)
 {
     int ret = -1;
 
@@ -728,7 +728,7 @@ int getifaddrs(struct ifaddrs **ifap)
             (parse_netlink_reply(&session, &ifaddrs_head, &last_ifaddr) < 0) ||
             (send_netlink_dump_request(&session, RTM_GETADDR) < 0) ||
             (parse_netlink_reply(&session, &ifaddrs_head, &last_ifaddr) < 0)) {
-        freeifaddrs (ifaddrs_head);
+        _netlink_freeifaddrs (ifaddrs_head);
         goto cleanup;
     }
 
@@ -744,7 +744,7 @@ int getifaddrs(struct ifaddrs **ifap)
     return ret;
 }
 
-void freeifaddrs(struct ifaddrs *ifa)
+void _netlink_freeifaddrs(struct ifaddrs *ifa)
 {
     struct ifaddrs *cur, *next;
 

src/native/libs/System.Native/pal_ifaddrs.h

@@ -7,37 +7,15 @@
 #error The pal_ifaddrs.h shim is intended only for Android
 #endif
 
+#if __ANDROID_API__ >= 24
+#error The pal_ifaddrs.h shim is only necessary for Android API 21-23 and it should be removed now that the minimum supported API level is 24 or higher
+#endif
+
 // Android doesn't include the getifaddrs and freeifaddrs functions in older Bionic libc (pre API 24).
-// In recent Android versions (Android 11+) the data returned by the getifaddrs function is not valid.
 // This shim is a port of Xamarin Android's implementation of getifaddrs using Netlink.
+// https://github.com/xamarin/xamarin-android/blob/681887ebdbd192ce7ce1cd02221d4939599ba762/src/monodroid/jni/xamarin_getifaddrs.h
 
-#include "pal_compiler.h"
-#include "pal_config.h"
-#include "pal_types.h"
-
-#include <sys/cdefs.h>
-#include <netinet/in.h>
-#include <sys/socket.h>
-
-struct ifaddrs
-{
-    struct ifaddrs *ifa_next;
-    char *ifa_name;
-    unsigned int ifa_flags;
-    struct sockaddr *ifa_addr;
-    struct sockaddr *ifa_netmask;
-    union
-    {
-        struct sockaddr *ifu_broadaddr;
-        struct sockaddr *ifu_dstaddr;
-    } ifa_ifu;
-    void *ifa_data;
-};
-
-// Synonym for `ifa_ifu.ifu_broadaddr` in `struct ifaddrs`.
-#define ifa_broadaddr ifa_ifu.ifu_broadaddr
-// Synonym for `ifa_ifu.ifu_dstaddr` in `struct ifaddrs`.
-#define ifa_dstaddr ifa_ifu.ifu_dstaddr
+#include <ifaddrs.h>
 
-int getifaddrs (struct ifaddrs **ifap);
-void freeifaddrs (struct ifaddrs *ifap);
+int _netlink_getifaddrs (struct ifaddrs **ifap);
+void _netlink_freeifaddrs (struct ifaddrs *ifap);

src/native/libs/System.Native/pal_interfaceaddresses.c

@@ -11,11 +11,13 @@
 #include <stdlib.h>
 #include <sys/types.h>
 #include <assert.h>
-#if HAVE_GETIFADDRS && !defined(TARGET_ANDROID)
+#if HAVE_GETIFADDRS || defined(ANDROID_GETIFADDRS_WORKAROUND)
 #include <ifaddrs.h>
 #endif
-#ifdef TARGET_ANDROID
-#include "pal_ifaddrs.h"
+#ifdef ANDROID_GETIFADDRS_WORKAROUND
+#include <dlfcn.h>
+#include <pthread.h>
+#include "pal_ifaddrs.h" // fallback for Android API 21-23
 #endif
 #include <net/if.h>
 #include <netinet/in.h>
@@ -100,12 +102,56 @@ static inline uint8_t mask2prefix(uint8_t* mask, int length)
     return len;
 }
 
+#ifdef ANDROID_GETIFADDRS_WORKAROUND
+// This workaround is necessary as long as we support Android API 21-23 and it can be removed once
+// we drop support for these old Android versions.
+static int (*getifaddrs)(struct ifaddrs**) = NULL;
+static void (*freeifaddrs)(struct ifaddrs*) = NULL;
+
+static void try_loading_getifaddrs()
+{
+    if (android_get_device_api_level() >= 24)
+    {
+        // Bionic on API 24+ contains the getifaddrs/freeifaddrs functions but the NDK doesn't expose those functions
+        // in ifaddrs.h when the minimum supported SDK is lower than 24 and therefore we need to load them manually
+        void *libc = dlopen("libc.so", RTLD_NOW);
+        if (libc)
+        {
+            getifaddrs = (int (*)(struct ifaddrs**)) dlsym(libc, "getifaddrs");
+            freeifaddrs = (void (*)(struct ifaddrs*)) dlsym(libc, "freeifaddrs");
+        }
+    }
+    else
+    {
+        // Bionic on API 21-23 doesn't contain the implementation of getifaddrs/freeifaddrs at all
+        // and we need to reimplement it using netlink (see pal_ifaddrs)
+        getifaddrs = _netlink_getifaddrs;
+        freeifaddrs = _netlink_freeifaddrs;
+    }
+}
+
+static bool ensure_getifaddrs_is_loaded()
+{
+    static pthread_once_t getifaddrs_is_loaded = PTHREAD_ONCE_INIT;
+    pthread_once(&getifaddrs_is_loaded, try_loading_getifaddrs);
+    return getifaddrs != NULL && freeifaddrs != NULL;
+}
+#endif
+
 int32_t SystemNative_EnumerateInterfaceAddresses(void* context,
                                                IPv4AddressFound onIpv4Found,
                                                IPv6AddressFound onIpv6Found,
                                                LinkLayerAddressFound onLinkLayerFound)
 {
-#if HAVE_GETIFADDRS || defined(TARGET_ANDROID)
+#ifdef ANDROID_GETIFADDRS_WORKAROUND
+    if (!ensure_getifaddrs_is_loaded())
+    {
+        errno = ENOTSUP;
+        return -1;
+    }
+#endif
+
+#if HAVE_GETIFADDRS || defined(ANDROID_GETIFADDRS_WORKAROUND)
     struct ifaddrs* headAddr;
     if (getifaddrs(&headAddr) == -1)
     {
@@ -250,7 +296,15 @@ int32_t SystemNative_EnumerateInterfaceAddresses(void* context,
 
 int32_t SystemNative_GetNetworkInterfaces(int32_t * interfaceCount, NetworkInterfaceInfo **interfaceList, int32_t * addressCount, IpAddressInfo **addressList )
 {
-#if HAVE_GETIFADDRS || defined(TARGET_ANDROID)
+#ifdef ANDROID_GETIFADDRS_WORKAROUND
+    if (!ensure_getifaddrs_is_loaded())
+    {
+        errno = ENOTSUP;
+        return -1;
+    }
+#endif
+
+#if HAVE_GETIFADDRS || defined(ANDROID_GETIFADDRS_WORKAROUND)
     struct ifaddrs* head;   // Pointer to block allocated by getifaddrs().
     struct ifaddrs* ifaddrsEntry;
     IpAddressInfo *ai;
@@ -289,7 +343,16 @@ int32_t SystemNative_GetNetworkInterfaces(int32_t * interfaceCount, NetworkInter
     // To save allocation need for separate free() we will allocate one memory chunk
     // where we first write out NetworkInterfaceInfo entries immediately followed by
     // IpAddressInfo list.
-    void * memoryBlock = calloc((size_t)count, sizeof(NetworkInterfaceInfo));
+#ifdef TARGET_ANDROID
+    // Since Android API 30, getifaddrs returns only AF_INET and AF_INET6 addresses and we do not
+    // get any AF_PACKET addresses and so count == ip4count + ip6count. We need to make sure that
+    // the memoryBlock is large enough to hold all interfaces (up to `count` entries) and all
+    // addresses (ip4count + ip6count) without any overlap between interfaceList and addressList.
+    int entriesCount = count + ip4count + ip6count;
+#else
+    int entriesCount = count;
+#endif
+    void * memoryBlock = calloc((size_t)entriesCount, sizeof(NetworkInterfaceInfo));
     if (memoryBlock == NULL)
     {
         errno = ENOMEM;
@@ -300,7 +363,7 @@ int32_t SystemNative_GetNetworkInterfaces(int32_t * interfaceCount, NetworkInter
     ifaddrsEntry = head;
     *interfaceList = nii = (NetworkInterfaceInfo*)memoryBlock;
     // address of first IpAddressInfo after all NetworkInterfaceInfo entries.
-    *addressList = ai = (IpAddressInfo*)(nii + (count - ip4count - ip6count));
+    *addressList = ai = (IpAddressInfo*)(nii + (entriesCount - ip4count - ip6count));
 
     while (ifaddrsEntry != NULL)
     {
@@ -324,7 +387,7 @@ int32_t SystemNative_GetNetworkInterfaces(int32_t * interfaceCount, NetworkInter
             memcpy(nii->Name, ifaddrsEntry->ifa_name, sizeof(nii->Name));
             nii->InterfaceIndex = if_nametoindex(ifaddrsEntry->ifa_name);
             nii->Speed = -1;
-            nii->HardwareType = NetworkInterfaceType_Unknown;
+            nii->HardwareType = ((ifaddrsEntry->ifa_flags & IFF_LOOPBACK) == IFF_LOOPBACK) ? NetworkInterfaceType_Loopback : NetworkInterfaceType_Unknown;
 
             // Get operational state and multicast support.
             if ((ifaddrsEntry->ifa_flags & (IFF_MULTICAST|IFF_ALLMULTI)) != 0)