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我正在使用共享内存在 linux 上不相关的进程之间进行通信。我只希望我在 struct ipc_perm 中指定的进程能够访问共享内存。但似乎代码无效：

进程A：创建共享内存

      int main (int argc, char* argv[]){
          int segment_id;
          key_t key;
          key = 56789;

          char* shared_memory;
          int shm_size = 512;

          segment_id = shmget(key, shm_size, IPC_CREAT | 0666);
          if (segment_id < 0){
             perror("shmget");
             exit(1);
          }else {
             struct shmid_ds shmbuf;
             struct ipc_perm perms;

             //here i specified the process whose
             //uid is 1234 has the read/write access
             //to this shared memory
             perms.uid = 1234;
             perms.gid = 2000;
             perms.mode = 0660;

             shmctl(segment_id, IPC_STAT, &shmbuf);
             shmbuf.shm_perm = perms;
             int ret = shmctl(segment_id, IPC_SET, &shmbuf);
             if (ret < 0){
                 perror("shmctl IPC_SET");
                 exit(1);
             } 
           }

           shared_memory = (char*)shmat(segment_id, NULL, 0);
           if (shared_memory == (char*) -1){
              perror("shmat");
              exit(1);
           }

           sprintf(shared_memory, "Server Updated The Memory -PID- %lu", getpid());
           while(*shared_memory != '*')
               sleep(1);

           printf("The memory has been updated: \n   %s\n", shared_memory);
           sleep(5);
           shmdt(shared_memory);
           shmctl(segment_id, IPC_RMID, 0);
           return 0;
      }

进程B：访问进程A创建的共享内存

          int main(){
              int segment_id;
              key_t key;
              key = 56789;

              char* shared_memory, *s;
              int shm_size = 512;

              segment_id = shmget(key, shm_size, 0666);
              if (segment_id < 0){
                   perror("shmget");
                   exit(1);
              }

              shared_memory = (char*)shmat(segment_id, NULL, 0);
              if (shared_memory == (char*) -1){
                   perror("shmat");
                   exit(1);
               }

              for (s = shared_memory; *s != NULL; s++)
                     putchar(*s);
              putchar('\n');

              sprintf(shared_memory, "*Client Updated The Memory - pid-%lu", getpid());
              return 0;
          }

在我的测试过程中，进程 B 始终具有对进程 A 创建的共享内存的读/写访问权限。为什么会发生这种情况？（我在ubuntu上运行，打开两个控制台分别启动上述进程。）

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1 回答 1

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If both processes have UID 1234, or GID 2000, then they should both have access to the shared memory segment. Your comment in the source: "the process whose uid is 1234" seems to indicate you are confusing the term UID (user identifier) with PID (process identifer).

To my knowledge there is no way to restrict access to a shared memory segment to a specific set of processes by PID. Restricting to processes run by a specific user - by specifying that user's ID in the shm_perm.uid when calling shm_ctl(...IPC_SET...) - is generally good enough. If want to restrict the processes that can access the segment, restrict which processes you run that access the segment.

于 2013-08-11T05:50:28.483 回答