【发布时间】：2021-04-04 07:05:34
【问题描述】：
通过复制到已初始化的指针，我得到了 segFault。这是相关代码
*pay = (char *)malloc(sizeof(t1) + 1020 /*1000=payload*/);
memset(*pay, 0, sizeof(t1) + 1020);
struct ethhdr *eth = (struct ethhdr *) *pay;
struct iphdr *ip = (struct iphdr *) (*pay + sizeof(struct ethhdr));
struct tcphdr *tcp = (struct tcphdr *) (*pay + sizeof(struct ethhdr) + sizeof(struct iphdr));
我做到了
memcpy(eth->h_dest, p->h_source, sizeof(eth->h_source));
但上面的行导致了段错误。我在其他线程memcpy((p)->h_source, received_packet_eth->h_source, sizeof(eth->h_source)); 中像这样分配h_source
h_source 在结构内部struct packets *p
这就是它的定义struct packets *p 我在其他线程中初始化和分配的方式，见上文。所以struct packets *p 不是一个未初始化的指针。我确信它是在发生 segFault 时分配的。
unsigned char h_source[ETH_ALEN]; /* source ether addr */
感谢您的帮助
更新这是函数的完整代码
void get_payload_to_send(struct packets *p, char **pay)
{
printf("%s --->>> %s", p->ip_source, p->ip_dest);
int t1;
*pay = (char *)malloc(sizeof(t1) + 1020 /*1000=payload*/);
memset(*pay, 0, sizeof(t1) + 1020);
struct ethhdr *eth = (struct ethhdr *) *pay;
struct iphdr *ip = (struct iphdr *) (*pay + sizeof(struct ethhdr));
struct tcphdr *tcp = (struct tcphdr *) (*pay + sizeof(struct ethhdr) + sizeof(struct iphdr));
//if (p->h_proto == ntohs(p->h_proto) == ETH_P_IP)
{
if (p->syn == 1 && p->ack == 0 && p->fin == 0)
{
///Ethernet
//memcpy(eth->h_dest, p->h_source, sizeof(eth->h_source));
eth->h_proto = htonl(ETH_P_IP);
//memcpy(eth->h_source, p->h_dest, sizeof(eth->h_dest));
////IP
// memcpy(ip->saddr, inet_addr(p->ip_dest), sizeof(ip->saddr));
struct sockaddr_in s1, s2;
s1.sin_family = AF_INET;
s1.sin_port = htons(80);
s1.sin_addr.s_addr = inet_addr(p->ip_source);
s2.sin_family = AF_INET;
s2.sin_port = htons(5009);
s2.sin_addr.s_addr = inet_addr(p->ip_dest);
//ip->saddr = s1.sin_addr.s_addr;
sleep(2);
ip->daddr = s2.sin_addr.s_addr;
char c[20];
memcpy(ip->saddr, inet_addr(p->ip_dest), sizeof(c) - 1);
ip->ihl = 5;
ip->version = 4;
ip->tos = 0;
ip->tot_len = sizeof(t1) + 1020;
srand(1001);
ip->id = htonl(rand());
ip->frag_off = 0;
ip->ttl = 225;
ip->protocol = IPPROTO_TCP;
ip->check = 0;
tcp->syn = 1;
tcp->ack = 1;
memcpy(ip->daddr, inet_addr(p->ip_source), sizeof(c) - 1);
//ip->check = csum((unsigned short *)*pay, ip->tot_len);
}
else if (p->syn == 0 && p->ack == 1)
{
}
}
//printf("%saddr %s -->>", p->ip_source);
//printf("daddr %s\n", p->ip_dest);
//populate eth
}
这是对上述函数进行函数调用的代码
void *task_sender(void *args) {
struct struct_super_struct *super = (struct struct_super_struct *)args;
struct packets *p = super->p; //(struct packets *)args;
printf("Sender\n");
while (1)
{
//printf("got uppder loop SENDER\n");
pthread_mutex_lock(&mutex);
while (nop == 0)
{
pthread_cond_wait(&cond, &mutex);
//printf("finished waiting in SENDER\n");
}
int i = 0;
printf("NOP is greater than 2 in SENDER %d\n");
while (nop > 0)
{
// check_and_process_connection(super,(p+i));
//if (p == NULL) break;
if (strcmp("192.168.10.25", (p+i)->ip_dest) == 0 && (p+i)->syn == 1 && (p+i)->ack == 0)
{
//sleep(1);
//printf("%s\n", (p+i)->ip_dest);
//if (strcmp((p+i)->ip_dest, "192.168.10.25") == 0)
{
char *pac;
struct packets *pt = (p+i);
get_payload_to_send((p+i), &pac);
struct sockaddr_in temp;
struct ethhdr *eth = (struct ethhdr *)pac;
struct iphdr *ip = (struct iphdr *)(pac + sizeof(struct ethhdr));
struct tcphdr *tcp = (struct tcphdr *)(pac + sizeof(struct ethhdr) + sizeof(struct iphdr));
temp.sin_addr.s_addr = ip->saddr;
char *source = inet_ntoa(temp.sin_addr);
struct sockaddr_in temp1;
temp1.sin_addr.s_addr = ip->daddr;
char *dest = inet_ntoa(temp1.sin_addr);
printf("%s >> %s \n", (p+i)->ip_source, (p+i)->ip_dest);
//if (strcmp("192.168.10.25",dest) == 0 && strcmp("192.168.10.25", source) == 0)
{
///temp1.sin_addr.s_addr = ip->daddr;
printf("should be\n");
printf("frm %s to %s syc:%d ack:%d \n",
inet_ntoa(temp.sin_addr),
inet_ntoa(temp1.sin_addr),
tcp->syn, tcp->ack);
}
/*
printf("__________________________________________________\n");
printf("lastop: %d\n", (p+i)->lastop);
printf("source: %s %d\n", (p+i)->ip_source, (p+i)->tcp_source);
printf("dest: %s %d\n", (p+i)->ip_dest, (p+i)->tcp_dest);
printf("syc: %d\n", (p+i)->syn);
printf("ack: %d\n", (p+i)->ack);
printf("seq: %d\n", (p+i)->seq);
printf("ack seq: %d\n", (p+i)->ack_seq);
(p+i)->lastop = 0;
printf("lastop: %d\n", (p+i)->lastop);
*/
}
//printf("dest port: %d\n", (p+i)->tcp_dest);
}
//else { printf("source ip: %s\n", (p+i)->ip_source); printf("dest ip: %s\n", (p+i)->ip_dest); }
//p++;
nop--;
i++;
//printf("just processed packet SENDER\n");
}
//p = NULL;
pthread_mutex_unlock(&mutex);
nop = 0;
int s = pthread_cond_signal(&cond);
}
}
更新 2
struct packets {
int syn;
char payload[1000];
// pthread_mutex_t mutex;
int lastop;
unsigned char h_dest[ETH_ALEN]; /* destination eth addr */
unsigned char h_source[ETH_ALEN]; /* source ether addr */
__be16 h_proto;
char ip_source[20];
char ip_dest[20];
int tcp_source;
int tcp_dest;
int seq;
int ack_seq;
int ack;
int fin;
int rst;
int window;
int nop;
struct ethhdr *eth;
struct iphdr *ip;
struct tcphdr *tcp;
}; // *p=NULL;
注意我发现用gdb调试的是memcpy(eth->h_dest, p->h_source, sizeof(eth->h_source));行eth->hdest是NULL
【问题讨论】：
-
*pay=(char *) malloc不要转换 malloc 的结果。 -
这很重要，为什么。这不是我得到 segFault 的原因。我是吗？
-
这段代码中的所有内容都是错误的。 我们没有看到 ethernet、ip 或 tcp 标头的声明，但不能保证您可以添加以太网的 14 字节大小标头并降落到与 IP 标头正确对齐的位置。
-
我确实看到了，因此我的 cmets 在那里。我上面所说的与Dude在那里所说的并不矛盾。您的代码不构成minimal reproducible example，它只是一些转储到问题框中。这很容易分辨，因为您甚至都不关心删除注释代码！
-
尝试通过 valgrind 运行您的代码。如果你对内存管理不善，它会告诉你在哪里。