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udp.cc中对接收数据的处理出现异常 #10

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virqin opened this issue Jun 23, 2016 · 4 comments
Closed

udp.cc中对接收数据的处理出现异常 #10

virqin opened this issue Jun 23, 2016 · 4 comments

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@virqin
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virqin commented Jun 23, 2016

        int fd = channel_->fd();
        ssize_t rn = recvfrom(fd, buf.makeRoom(kUdpPacketSize), buf.space(), 0, (sockaddr*)&raddr, &rsz);
        if (rn < 0) {
            error("udp %d recv failed: %d %s", fd, errno, strerror(errno));
            return;
        }
        buf.addSize(rn); //测试到有时recvfrom返回为0,即rn=0,addSize就会把buf内存搞砸
        trace("udp %d recv %ld bytes from %s", fd, rn, Ip4Addr(raddr).toString().data());
        this->msgcb_(shared_from_this(), buf, raddr);

释放内存错误*** Error in./udp-cli': double free or corruption (top): 0x0000000000f555e0 ***`

顺带问一下,什么情况下recvfrom返回0? 设定了非阻塞模式?我抓包看一下发送端

@dtm-labs
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看了相关的代码,并没有发现buf.addSize在处理rn=0的逻辑有问题。你能否提供重现问题的例子呢?

@virqin
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virqin commented Jun 24, 2016

@yedf 昨晚找了一下出问题的情况,我这边使用udp-svr/udp-cli进行测试收发,问题在于下面makeRoom和space执行的顺序:
ssize_t rn = recvfrom(fd, buf.makeRoom(kUdpPacketSize), buf.space(), 0, (sockaddr*)&raddr, &rsz);
这样没有问题:

char *pbuf = buf.makeRoom(kUdpPacketSize);
ssize_t rn = recvfrom(fd, pbuf, buf.space(), 0, (sockaddr*)&raddr, &rsz);

深究的话似乎是参数压栈顺序从右向左,而space方法依赖makeRoom,就是先调用space的话返回0

延伸:你那边没有问题吗?并且UDP允许发送0字节的数据,rn=0的话就会出现释放内存错误*** Error in./udp-cli': double free or corruption (top): 0x0000000000f555e0 ***

使用库的makefile编译的:

debian:~$ gcc --version
gcc (Debian 4.9.2-10) 4.9.2

@dtm-labs
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dtm-labs commented Jun 25, 2016

我原先的代码直接调用space是有问题的,你的修复方式是可行的,已经修复为
ssize_t rn = recvfrom(fd, buf.makeRoom(kUdpPacketSize), kUdpPacketSize, 0, (sockaddr*)&raddr, &rsz);
rn=0导致了buffer在复制时的一个bug,已经修复
谢谢你的issue

@virqin
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virqin commented Jun 25, 2016

👍

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