c - 无法解决客户端-服务器程序上大小为 1 的无效读取

Question

客户端和服务器通过发送这种类型的结构来交换消息：

typedef struct {
    op_t     op;   
    char sender[MAX_NAME_LENGTH+1];
} message_hdr_t;

typedef struct {
    char receiver[MAX_NAME_LENGTH+1];
    unsigned int   len;  
} message_data_hdr_t;

typedef struct {
    message_data_hdr_t  hdr;
    char               *buf;
} message_data_t;

typedef struct {
    message_hdr_t  hdr;
    message_data_t data;
} message_t;

客户端和服务器之间交换的消息正确到达并继续执行，但 valgrind returns 错误：

==4179== Invalid read of size 1
==4179==    at 0x4C32D04: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4179==    by 0x50B84D2: vfprintf (vfprintf.c:1643)
==4179==    by 0x50BFF25: printf (printf.c:33)
==4179==    by 0x10A122: threadF (main.c:151)
==4179==    by 0x4E436DA: start_thread (pthread_create.c:463)
==4179==    by 0x517C88E: clone (clone.S:95)
==4179==  Address 0x5452134 is 0 bytes after a block of size 4 alloc'd
==4179==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4179==    by 0x109B2B: readData (connections.h:103)
==4179==    by 0x109C17: readMsg (connections.h:134)
==4179==    by 0x10A0B0: threadF (main.c:146)
==4179==    by 0x4E436DA: start_thread (pthread_create.c:463)
==4179==    by 0x517C88E: clone (clone.S:95)

这就是我在 readData() 中填充服务器结构的方式；你可以把readn当作已读。

#define SYSCALL(r,c,msg) \
    if((r=c)==-1) {perror(msg);

//other reads and writes
msg->data.buf=malloc(msg->data.hdr.len*sizeof(char));
SYSCALL(notused,readn(fd,msg->data.buf,msg->data.hdr.len*sizeof(char)),"read_data_buf");            
if(notused==0){
    return -1;
}

当我在 main.c:151

上执行 printf 时出现错误

printf("BODY: %s\n",msg->data.buf);

Answer 1

可能

msg->data.buf=malloc(msg->data.hdr.len*sizeof(char));
SYSCALL(notused,readn(fd,msg->data.buf,msg->data.hdr.len*sizeof(char)),"read_data_buf");

必须

msg->data.buf=malloc(msg->data.hdr.len + 1);
SYSCALL(notused,readn(fd,msg->data.buf,msg->data.hdr.len),"read_data_buf");            
msg->data.buf[msg->data.hdr.len] = 0;

为结束空字符添加位置并设置它

但是你确定msg->data.buf是一个可打印的字符串吗？您如何在交换期间对您的结构进行编码？

同样sizeof(char)根据定义是1，乘以它是没有用的

Answer 2

根据这条消息

==4179==  Address 0x5452134 is 0 bytes after a block of size 4 alloc'd

你已经分配了 4 个字节。

您的 printf 电话

printf("BODY: %s\n",msg->data.buf);

期望找到以 [=13=]

结尾的字符串

可能你用SYSCALL(notused,readn(...读取的字节在这4个字节中不包含'[=15=]'，所以strlen读取分配内存结束后的下一个字节。

解决此问题的一个选择是再分配一个字节并将 '[=15=]' 附加到接收到的数据。

c - 无法解决客户端-服务器程序上大小为 1 的无效读取

c - can't solve Invalid read of size 1 on a client-server program

c

client

valgrind

server