Re: [Qemu-devel] [V3 PATCH 2/8] virtio-9p: Provide chroot environment server side interfaces

[Blue Swirl <blauwirbel@gmail.com>]

On Tue, Jan 18, 2011 at 6:25 AM, M. Mohan Kumar <mohan@in.ibm.com> wrote:
> Implement chroot server side interfaces like sending the file
> descriptor to qemu process, reading the object request from socket etc.
> Also add chroot main function and other helper routines.
>
> Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>
> ---
>  Makefile.objs              |    1 +
>  hw/9pfs/virtio-9p-chroot.c |  183 ++++++++++++++++++++++++++++++++++++++++++++
>  hw/9pfs/virtio-9p-chroot.h |   39 +++++++++
>  hw/9pfs/virtio-9p.c        |   23 ++++++
>  hw/file-op-9p.h            |    2 +
>  5 files changed, 248 insertions(+), 0 deletions(-)
>  create mode 100644 hw/9pfs/virtio-9p-chroot.c
>  create mode 100644 hw/9pfs/virtio-9p-chroot.h
>
> diff --git a/Makefile.objs b/Makefile.objs
> index bc0344c..3007b6d 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -273,6 +273,7 @@ hw-obj-$(CONFIG_SOUND) += $(sound-obj-y)
>  9pfs-nested-$(CONFIG_VIRTFS) = virtio-9p-debug.o
>  9pfs-nested-$(CONFIG_VIRTFS) +=  virtio-9p-local.o virtio-9p-xattr.o
>  9pfs-nested-$(CONFIG_VIRTFS) +=   virtio-9p-xattr-user.o virtio-9p-posix-acl.o
> +9pfs-nested-$(CONFIG_VIRTFS) +=   virtio-9p-chroot.o
>
>  hw-obj-$(CONFIG_REALLY_VIRTFS) += $(addprefix 9pfs/, $(9pfs-nested-y))
>  $(addprefix 9pfs/, $(9pfs-nested-y)): CFLAGS +=  -I$(SRC_PATH)/hw/
> diff --git a/hw/9pfs/virtio-9p-chroot.c b/hw/9pfs/virtio-9p-chroot.c
> new file mode 100644
> index 0000000..dcde2cc
> --- /dev/null
> +++ b/hw/9pfs/virtio-9p-chroot.c
> @@ -0,0 +1,183 @@
> +/*
> + * Virtio 9p chroot environment for contained access to exported path
> + *
> + * Copyright IBM, Corp. 2011
> + *
> + * Authors:
> + * M. Mohan Kumar <mohan@in.ibm.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2. See
> + * the copying file in the top-level directory
> + *
> + */
> +
> +#include <sys/fsuid.h>
> +#include <sys/resource.h>
> +#include <signal.h>
> +#include "virtio.h"
> +#include "qemu_socket.h"
> +#include "qemu-thread.h"
> +#include "qerror.h"
> +#include "virtio-9p.h"
> +#include "virtio-9p-chroot.h"
> +
> +/*
> + * Structure used by chroot functions to transmit file descriptor and
> + * error info
> + */
> +typedef struct {
> +    int fi_fd;
> +    int fi_error;
> +} FdInfo;
> +
> +union MsgControl {
> +    struct cmsghdr cmsg;
> +    char control[CMSG_SPACE(sizeof(int))];
> +};
> +
> +/* Send file descriptor and error status to qemu process */
> +static int chroot_sendfd(int sockfd, FdInfo *fd_info)

const FdInfo *?

> +{
> +    struct msghdr msg = { };
> +    struct iovec iov;
> +    struct cmsghdr *cmsg;
> +    int retval;
> +    union MsgControl msg_control;
> +
> +    iov.iov_base = fd_info;
> +    iov.iov_len = sizeof(*fd_info);
> +
> +    memset(&msg, 0, sizeof(msg));
> +    msg.msg_iov = &iov;
> +    msg.msg_iovlen = 1;
> +    /* No ancillary data on error */
> +    if (!fd_info->fi_error) {
> +        msg.msg_control = &msg_control;
> +        msg.msg_controllen = sizeof(msg_control);
> +
> +        cmsg = &msg_control.cmsg;
> +        cmsg->cmsg_len = CMSG_LEN(sizeof(fd_info->fi_fd));
> +        cmsg->cmsg_level = SOL_SOCKET;
> +        cmsg->cmsg_type = SCM_RIGHTS;
> +        memcpy(CMSG_DATA(cmsg), &fd_info->fi_fd, sizeof(fd_info->fi_fd));
> +    }
> +    retval = sendmsg(sockfd, &msg, 0);
> +    close(fd_info->fi_fd);
> +    return retval;
> +}
> +
> +/* Read V9fsFileObjectRequest written by QEMU process */
> +static void chroot_read_request(int sockfd, V9fsFileObjectRequest *request)
> +{
> +    int retval;
> +    retval = qemu_read_full(sockfd, request, sizeof(request->data));
> +    if (retval <= 0 || request->data.path_len <= 0) {
> +        _exit(-1);
> +    }
> +    request->path.path = qemu_mallocz(request->data.path_len + 1);
> +    retval = qemu_read_full(sockfd, (void *)request->path.path,
> +                        request->data.path_len);
> +    if (retval <= 0) {
> +        _exit(-1);
> +    }
> +    if (request->data.oldpath_len > 0) {
> +        request->path.old_path =
> +                qemu_mallocz(request->data.oldpath_len + 1);
> +        retval = qemu_read_full(sockfd, (void *)request->path.old_path,
> +                            request->data.oldpath_len);
> +        if (retval <= 0) {
> +            _exit(-1);
> +        }
> +    }
> +}
> +
> +static int chroot_daemonize(int chroot_sock)
> +{
> +    sigset_t sigset;
> +    struct rlimit nr_fd;
> +    int fd;
> +
> +    /* Block all signals for this process */
> +    sigprocmask(SIG_SETMASK, &sigset, NULL);
> +
> +    /* Daemonize */
> +    if (setsid() < 0) {
> +        error_report("setsid %s", strerror(errno));
> +        return -1;
> +    }
> +
> +    /* Close other file descriptors */
> +    getrlimit(RLIMIT_NOFILE, &nr_fd);
> +    for (fd = 0; fd < nr_fd.rlim_cur; fd++) {
> +        if (fd != chroot_sock) {
> +            close(fd);
> +        }
> +    }
> +
> +    /* Create files with mode as requested by client */
> +    umask(0);
> +    return 0;
> +}
> +
> +static void chroot_dummy(void)
> +{
> +    (void)chroot_sendfd;
> +}
> +
> +/*
> + * Fork a process and chroot into the share path. Communication
> + * between qemu process and chroot process happens via socket
> + */
> +int v9fs_chroot(FsContext *fs_ctx)
> +{
> +    int fd_pair[2], pid, chroot_sock, error;

The type of pid should be pid_t.

> +    V9fsFileObjectRequest request;
> +
> +    if (socketpair(PF_UNIX, SOCK_STREAM, 0, fd_pair) < 0) {
> +        error_report("socketpair %s", strerror(errno));
> +        return -1;
> +    }
> +
> +    pid = fork();
> +    if (pid < 0) {
> +        error_report("fork %s", strerror(errno));
> +        return -1;
> +    }
> +    if (pid != 0) {
> +        fs_ctx->chroot_socket = fd_pair[0];
> +        close(fd_pair[1]);
> +        return 0;
> +    }
> +
> +    close(fd_pair[0]);
> +    chroot_sock = fd_pair[1];
> +    if (chroot(fs_ctx->fs_root) < 0) {
> +        error_report("chroot %s", strerror(errno));
> +        return -1;
> +    }
> +
> +    chroot_dummy();
> +    if (chroot_daemonize(chroot_sock) < 0) {
> +        _exit(-1);
> +    }
> +
> +    /*
> +     * Write 0 to chroot socket to indicate chroot process creation is
> +     * successful
> +     */
> +    error = 0;
> +    if (qemu_write_full(chroot_sock, &error, sizeof(error)) != sizeof(error)) {
> +        _exit(-1);
> +    }
> +    /* get the request from the socket */
> +    while (1) {
> +        chroot_read_request(chroot_sock, &request);
> +        qemu_free(request.path.path);
> +        if (request.data.oldpath_len) {
> +            qemu_free(request.path.old_path);
> +        }
> +        if (error) {
> +            _exit(error);
> +        }
> +    }
> +}
> diff --git a/hw/9pfs/virtio-9p-chroot.h b/hw/9pfs/virtio-9p-chroot.h
> new file mode 100644
> index 0000000..3bee5e3
> --- /dev/null
> +++ b/hw/9pfs/virtio-9p-chroot.h
> @@ -0,0 +1,39 @@
> +#ifndef _QEMU_VIRTIO_9P_CHROOT_H
> +#define _QEMU_VIRTIO_9P_CHROOT_H
> +
> +/* types for V9fsFileObjectRequest */
> +#define T_OPEN      1
> +#define T_CREATE    2
> +#define T_MKDIR     3
> +#define T_MKNOD     4
> +#define T_SYMLINK   5
> +#define T_LINK      6
> +
> +struct V9fsFileObjectData
> +{
> +    int flags;
> +    int mode;
> +    uid_t uid;
> +    gid_t gid;
> +    dev_t dev;
> +    int path_len;
> +    int oldpath_len;
> +    int type;
> +};
> +
> +struct V9fsFileObjectPath
> +{
> +    char *path;
> +    char *old_path;

Can these be const char *?