• 本地库覆盖glibc的API

    本地库覆盖glibc的getifaddrs

    基本原理：（原理类似libSegFault.so这个库）

    使用linux的环境变量“LD_PRELOAD”来提前载入一个库，然后这个库里面的同名API就可以覆盖后续的共享库的API了(glibc里面的若链接的API是可以被覆盖的)。如我们在自己的共享库中重写一个API

    int getifaddrs (struct ifaddrs **ifap)；

    主要修改代码点：

    1. 在一个新的共享库里重写/覆盖getifaddrs(), 生产一个共享库libovfuns.so，把它拷贝到/opt/lib里面。主要修改点事去掉原有glibc里__netlink_assert_response(...)的abort处理，同时是在系统的文件里面记录一条异常log：（/opt/log/overwirte_fun.log）

      1. static void __netlink_assert_response (int fd, ssize_t result)
      2. {
      3.   if (result < 0)
      4.     {
      5.       /* Check if the error is unexpected.  */
      6.       bool terminate = false;
      7.       int error_code = errno;
      8.       int family = get_address_family (fd);
      9.       if (family != AF_NETLINK)
      10.         /* If the address family does not match (or getsockname
      11.            failed), report the original error.  */
      12.         terminate = true;
      13.       else if (error_code == EBADF
      14.           || error_code == ENOTCONN
      15.           || error_code == ENOTSOCK
      16.           || error_code == ECONNREFUSED)
      17.         /* These errors indicate that the descriptor is not a
      18.            connected socket.  */
      19.         terminate = true;
      20.       else if (error_code == EAGAIN || error_code == EWOULDBLOCK)
      21.         {
      22.           /* The kernel might return EAGAIN for other reasons than a
      23.              non-blocking socket.  But if the socket is not blocking,
      24.              it is not ours, so report the error.  */
      25.           int mode = fcntl (fd, F_GETFL, 0);
      26.           if (mode < 0 || (mode & O_NONBLOCK) != 0)
      27.             terminate = true;
      28.         }
      29. 	    printf("[%s %d]\n", __func__, __LINE__);
      30.       if (terminate)
      31.         {
      32.           char message[200];
      33.           if (family < 0)
      34.             snprintf (message, sizeof (message),
      35.                         "Inovance overwrite： Unexpected error %d on netlink descriptor %d",
      36.                         error_code, fd);
      37.           else
      38.             snprintf (message, sizeof (message),
      39.                         "Inovance overwrite： Unexpected error %d on netlink descriptor %d"
      40.                         " (address family %d)",
      41.                         error_code, fd, family);
      42.     //just use the log message replace the "__libc_fatal"
      43.         //    __libc_fatal (message);
      44.         overwrite_fun_log("getifaddrs", message);
      45.  
      46.         }
      47.       else
      48.         /* Restore orignal errno value.  */
      49.         set_errno (error_code);
      50.     }
      51.   else if (result < sizeof (struct nlmsghdr))
      52.     {
      53.       char message[200];
      54.       int family = get_address_family (fd);
      55.       if (family < 0)
      56.           snprintf (message, sizeof (message),
      57.                       "Inovance overwrite： Unexpected netlink response of size %zd"
      58.                       " on descriptor %d",
      59.                       result, fd);
      60.       else
      61.           snprintf (message, sizeof (message),
      62.                       "Inovance overwrite： Unexpected netlink response of size %zd"
      63.                       " on descriptor %d (address family %d)",
      64.                       result, fd, family);
      65.     //just use the log message replace the "__libc_fatal"
      66.     //   __libc_fatal (message);
      67.         overwrite_fun_log("getifaddrs", message);
      68.     }
      69. }

    2. 修改test启动的服务脚本：在原有服务脚本里面增加如下行，用于设置环境变量Environment="LD_PRELOAD=/opt/runtime/libovfuns.so"

      1. root@xxx:# cat /lib/systemd/system/test.service
      2. [Unit]
      3. Description=Inovance CoDeSys Control Progres
      4. Wants=inovance-daemon.service
      5. After=inovance-daemon.service
      6.  
      7. [Service]
      8. Type=simple
      9. Environment="LD_PRELOAD=/opt/lib/libovfuns.so"
      10. PIDFile=/run/test.pid
      11. ExecStartPre=/bin/sleep 5
      12. ExecStart=/opt/xxx/test
      13. StandardOutput=null
      14. StandardError=null
      15. #Restart=always
      16. #RestartSec=1
      17. #StartLimitInterval=0
      18.  
      19. [Install]
      20. WantedBy=multi-user.target
      21.

    4. 下面是测试代码，编译时使用gcc -L/opt/runtime/ -I./lib -lovfuns -o test test.c

    5. 生产test测试程序

      1.  #define _GNU_SOURCE     /* To get defns of NI_MAXSERV and NI_MAXHOST */
      2.        #include <arpa/inet.h>
      3.        #include <sys/socket.h>
      4.        #include <netdb.h>
      5.        #include "my_ifaddrs.h"
      6.        #include <stdio.h>
      7.        #include <stdlib.h>
      8.        #include <unistd.h>
      9.        #include <linux/if_link.h>
      10.  
      11.  
      12.        int main(int argc, char *argv[])
      13.        {
      14.            struct ifaddrs *ifaddr, *ifa;
      15.            int family, s, n;
      16.            char host[NI_MAXHOST];
      17.  
      18.            if (getifaddrs(&ifaddr) == -1) {
      19.                perror("getifaddrs");
      20.                exit(EXIT_FAILURE);
      21.            }
      22.  
      23.            /* Walk through linked list, maintaining head pointer so we
      24.               can free list later */
      25.  
      26.            for (ifa = ifaddr, n = 0; ifa != NULL; ifa = ifa->ifa_next, n++) {
      27.                if (ifa->ifa_addr == NULL)
      28.                    continue;
      29.  
      30.                family = ifa->ifa_addr->sa_family;
      31.  
      32.                /* Display interface name and family (including symbolic
      33.                   form of the latter for the common families) */
      34.  
      35.                printf("%-8s %s (%d)\n",
      36.                       ifa->ifa_name,
      37.                       (family == AF_PACKET) ? "AF_PACKET" :
      38.                       (family == AF_INET) ? "AF_INET" :
      39.                       (family == AF_INET6) ? "AF_INET6" : "???",
      40.                       family);
      41.  
      42.                /* For an AF_INET* interface address, display the address */
      43.  
      44.                if (family == AF_INET || family == AF_INET6) {
      45.                    s = getnameinfo(ifa->ifa_addr,
      46.                            (family == AF_INET) ? sizeof(struct sockaddr_in) :
      47.                                                  sizeof(struct sockaddr_in6),
      48.                            host, NI_MAXHOST,
      49.                            NULL, 0, NI_NUMERICHOST);
      50.                    if (s != 0) {
      51.                        printf("getnameinfo() failed: %s\n", gai_strerror(s));
      52.                        exit(EXIT_FAILURE);
      53.                    }
      54.  
      55.                    printf("\t\taddress: <%s>\n", host);
      56.  
      57.                } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
      58.                    struct rtnl_link_stats *stats = ifa->ifa_data;
      59.  
      60.                    printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
      61.                           "\t\ttx_bytes   = %10u; rx_bytes   = %10u\n",
      62.                           stats->tx_packets, stats->rx_packets,
      63.                           stats->tx_bytes, stats->rx_bytes);
      64.                }
      65.            }
      66.  
      67.            freeifaddrs(ifaddr);
      68.            exit(EXIT_SUCCESS);
      69.        }

      测试添加和不添加环境量，程序使用的API是不同的，具体测试log如下所示：

      不添加环境变量，程序使用原始API

      root@xxx:# ./test

      lo AF_PACKET (17)

      tx_packets = 65; rx_packets = 65

      tx_bytes = 3180; rx_bytes = 3180

      enp1s0 AF_PACKET (17)

      tx_packets = 686; rx_packets = 3008

      tx_bytes = 50762; rx_bytes = 192738

      enp2s0 AF_PACKET (17)

      tx_packets = 118; rx_packets = 204

      tx_bytes = 19366; rx_bytes = 22391

      enp3s0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      enp4s0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 16

      tx_bytes = 0; rx_bytes = 960

      tunl0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      tap0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      tap1 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      lo AF_INET (2)

      address: <127.0.0.1>

      enp1s0 AF_INET (2)

      address: <10.61.64.75>

      enp2s0 AF_INET (2)

      address: <192.168.2.88>

      添加环境变量，程序使用新的API

      root@xxx:# env LD_PRELOAD=/opt/runtime/libovfuns.so ./test

      [__netlink_request 601] <------这个log是新的API里面的

      [__netlink_request 604]

      [__netlink_request 601]

      [__netlink_request 604]

      [__netlink_request 601]

      [__netlink_request 604]

      [__netlink_request 601]

      [__netlink_request 604]

      [__netlink_request 601]

      [__netlink_request 604]

      lo AF_PACKET (17)

      tx_packets = 107; rx_packets = 107

      tx_bytes = 5196; rx_bytes = 5196

      enp1s0 AF_PACKET (17)

      tx_packets = 1138; rx_packets = 4968

      tx_bytes = 83894; rx_bytes = 316171

      enp2s0 AF_PACKET (17)

      tx_packets = 160; rx_packets = 251

      tx_bytes = 23366; rx_bytes = 26263

      enp3s0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      enp4s0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 24

      tx_bytes = 0; rx_bytes = 1440

      tunl0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      tap0 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      tap1 AF_PACKET (17)

      tx_packets = 0; rx_packets = 0

      tx_bytes = 0; rx_bytes = 0

      lo AF_INET (2)

      address: <127.0.0.1>

      enp1s0 AF_INET (2)

      address: <10.61.64.75>

      enp2s0 AF_INET (2)

      address: <192.168.2.88>

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  • 原文地址：https://blog.csdn.net/paky_du/article/details/127808596