SOCK_STREAM TCP: send() returns success even when other side responded with RST packet

[Tomas Hozza <thozza@redhat.com>]

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Hi.

I was advised to forward my networking Kernel related Bug here
so it can get fixed much faster. Here is the Bug description
copied from Red Hat Bugzilla (https://bugzilla.redhat.com/show_bug.cgi?id=912382):

Description of problem:
I'm using SOCK_STREAM TCP sockets. Imagine server-client application.
- Server will accept connection from client.
- Client sends some data to server -> server receives data.
- Client then half-closes the TCP connection using shutdown(fd, SHUT_WR).
- Client waits for some data from the server.
- Server sends some data to client -> client receives data.
- Client exits and closes the socket.
- After some time server tries to send some data to the client.
- The first send() call returns success even the Client's response is RST.


Version-Release number of selected component (if applicable):
3.7.7-201.fc18.x86_64
3.7.8-202.fc18.x86_64


How reproducible:
always


Steps to Reproduce:
1. download attached client/server sources.
2. compile server: # gcc tcp_server.c -o server
3. compile client: # gcc tcp_client.c -o client
4. run the server: # ./server
5. run the client: # ./client


Actual results:
Server started...
Created SOCK_STREAM socket
Bound to localhost:6666
waiting for connection...
Client connected!
Waiting for some data from client
Received: "MSG from client"
Received EOF
Sending msg to client: "MSG from server"
sleep(5)
Sending 1 msg to client: "MSG from server"
try #1 send() result: (0) Success
Sending 2 msg to client: "MSG from server"
try #2 send() result: (32) Broken pipe
Server exiting...


Expected results:
Server should fail to send() data right after sleep().

Server started...
Created SOCK_STREAM socket
Bound to localhost:6666
waiting for connection...
Client connected!
Waiting for some data from client
Received: "MSG from client"
Received EOF
Sending msg to client: "MSG from server"
sleep(5)
Sending 1 msg to client: "MSG from server"
try #1 send() result: (32) Broken pipe
Server exiting...


Additional info:
RST answer means that data were NOT delivered. Therefore the very
first send() call after server sleep() should fail!


Regards,

Tomas Hozza

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[-- Attachment #2: tcp_server.c --]
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#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <signal.h>

int main(int argc, char **argv)
{
    int ssock, csock, i;
    static char buff[256];
    ssize_t nbytes;
    struct sockaddr_in saddr;

    memset(&saddr, 0, sizeof(saddr));
    saddr.sin_family = AF_INET;
    saddr.sin_port = htons(6666);

    signal(SIGPIPE, SIG_IGN);

    printf("Server started...\n");

    if ((ssock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        printf("socket() error. (%d) %s\n", errno, strerror(errno));
        exit(1);
    }
    printf("Created SOCK_STREAM socket\n");

    if (bind(ssock, (struct sockaddr*)&saddr, sizeof(saddr)) == -1) {
        printf("bind() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        exit(1);
    }
    printf("Bound to localhost:6666\n");

    if (listen(ssock, 1) == -1) {
        printf("listen() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        exit(1);
    }

    printf("waiting for connection...\n");
    csock = accept(ssock, NULL, NULL);

    if (csock == -1) {
        printf("accept() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        exit(1);
    }
    printf("Client connected!\n");
    printf("Waiting for some data from client\n");

    while ((nbytes = recv(csock, buff, sizeof(buff), 0)) > 0) {
            printf("Received: \"%s\"\n", buff);
    }

    if (nbytes < 0) {
        printf("recv() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        close(csock);
        exit(1);
    } else if (nbytes == 0) {
        printf("Received EOF\n");
        printf("Sending msg to client: \"MSG from server\"\n");
        if ((nbytes = send(csock, "MSG from server", sizeof("MSG from server"), 0)) <= 0) {
            printf("send() error. (%d) %s\n", errno, strerror(errno));
            close(ssock);
            close(csock);
            exit(1);
        }
    }

    printf("sleep(5)\n");
    sleep(5);
    
    i = 1;
    while (1) { 
        printf("Sending %d msg to client: \"MSG from server\"\n", i);
        nbytes = send(csock, "MSG from server", sizeof("MSG from server"), 0);
        printf("try #%d send() result: (%d) %s\n",i ,errno, strerror(errno));
        if (nbytes <= 0)
            break;
        ++i;
    }

    printf("Server exiting...\n");
    close(ssock);
    close(csock);
    return 0;
}

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[-- Attachment #3: tcp_client.c --]
[-- Type: text/x-csrc; name=tcp_client.c, Size: 1694 bytes --]

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

int main(int argc, char **argv)
{
    int ssock, i;
    static char buff[256];
    ssize_t nbytes;
    struct sockaddr_in saddr;

    memset(&saddr, 0, sizeof(saddr));
    saddr.sin_family = AF_INET;
    saddr.sin_port = htons(6666);

    printf("Client started...\n");

    if ((ssock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        printf("socket() error. (%d) %s\n", errno, strerror(errno));
        exit(1);
    }

    printf("Created SOCK_STREAM socket\n");

    if (connect(ssock, (struct sockaddr *)&saddr, sizeof(saddr)) == -1) {
        printf("connect() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        exit(1);
    }

    printf("Connected to the server!\n");
    printf("Sending some data to server\n");

    if ((nbytes = send(ssock, "MSG from client", sizeof("MSG from client"), 0)) <= 0) {
        printf("send() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        exit(1);
    }

    printf("Half-closing connection with shutdown(ssock, SHUT_WR)\n");

    if (shutdown(ssock, SHUT_WR) == -1) {
        printf("shutdown() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        exit(1);
    }

    printf("Receiving data from server\n");
    if ((nbytes = recv(ssock, buff, sizeof(buff), 0)) > 0) {
            printf("Received: \"%s\"\n", buff);
    } else {
        printf("recv() error. (%d) %s\n", errno, strerror(errno));
        close(ssock);
        exit(1);
    }

    printf("Client exiting...\n");
    close(ssock);
    return 0;
}