c - 如何在尝试使用返回权限被拒绝的 popen 函数时处理无效/垃圾值

Question

我正在尝试编写一个程序来查找用户拥有的文件。然后将输出打印到变量中以对其进行操作或与其他程序进行通信。问题是当我将目录设置为 / 时，大多数早期查找都会被拒绝权限。但似乎有一个 NULL/垃圾或分配给变量的东西，即使它声明权限被拒绝。代码如下:

static struct{
          char file_owned[8192][1024];
}information;

void get_file_owned(char *username)
{
  FILE *stream3;
  extern FILE *popen();
  char command[1024];
  char buff[1024];
  int i;

  sprintf(command, "find / -user %s -ls",username);
  if(!(stream3 = popen(command), "r"))){
       exit(1);
  }
  i=0;
  while(fgets(buff, sizeof(buff), stream3)!=NULL){
       sprintf(information.file_owned[i],"%s",buff); //it print something into file_owned. But I do now know what. 
       i++;
  }
  pclose(stream3);
  return;
}

int main(int argc, char **argv)
{
  static char *username;
  int i;

  username = "fikrie";
  get_file_owned(username);

  for(i=0;i<10;i++){
    printf("%s\n",information.process_owned[i]);
  }
  return 0;
 }

这是输出:

find: `/proc/1657/task/1659/ns` : Permission denied
find: `/proc/1713/task/1713/ns` : Permission denied
...
...
//There's a lot of this kind of output
...
Segmentation fault(core dumped)

我预计这是由于权限被拒绝引起的。然后它只会将垃圾打印到 process_owned 中。我应该如何处理权限被拒绝的输出？我试图在 get_file_owned 函数中处理 NULL 。但这并不能解决问题。

while(fgets(buff, sizeof(buff), stream3)!=NULL){
    if(buff == NULL){
    continue;
    }
    sprintf(information.file_owned[i],"%s",buff);
    i++;
}

我还尝试使用 gdb 来查看段错误。这是结果:

warning: Can't read pathname for load map: Input/output error
Core was generated by `./a.out'.
Program terminated with signal 11, Segmentation fault.
#0 _IO_getline info (fp=0x9ec50b8, buf=0x2 <Address 0x2 out of bounds>, n=254, delim=10, extract_delim=1, eof=0x0) at iogetline.c:91
iogetline.c: No such file or directory.

请注意，如果我尝试在我的主目录中运行它。 /home/fikrie/Documents。没有段错误或错误。

编辑:我也以 root 身份运行这个程序。将结构方式改为这种类型:

struct{
   char file_owned[1024];
}information[1024];   //I tried changing this into 8094 also. Just in case the array for this struct is not enough. 

Answer 1

find 可能返回超过 8192 行。因此，while 循环会溢出数组 file_owned。