Re: [Qemu-devel] [PATCH] qemu-ga: obey LISTEN_PID when using systemd socket activation

["Richard W.M. Jones" <rjones@redhat.com>]

On Thu, Mar 16, 2017 at 05:15:35PM +0100, Paolo Bonzini wrote:
> qemu-ga's socket activation support was not obeying the LISTEN_PID
> environment variable, which avoids that a process uses a socket-activation
> file descriptor meant for its parent.
> 
> Mess can for example ensue if a process forks a children before consuming
> the socket-activation file descriptor and therefore setting O_CLOEXEC
> on it.
> 
> Luckily, qemu-nbd also got socket activation code, and its copy does
> support LISTEN_PID.  Some extra fixups are needed to ensure that the
> code can be used for both, but that's what this patch does.  The
> main change is to replace get_listen_fds's "consume" argument with
> the FIRST_SOCKET_ACTIVATION_FD macro from the qemu-nbd code.
> 
> Cc: "Richard W.M. Jones" <rjones@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Yes, it looks alright to me.

Shame we can't support LISTEN_FDS > 1 :-(

  Reviewed-by: Richard W.M. Jones <rjones@redhat.com>

Rich.

>  include/qemu/systemd.h |  26 +++++++++++++
>  qemu-nbd.c             | 100 ++++---------------------------------------------
>  qga/main.c             |  51 +++++++------------------
>  util/Makefile.objs     |   1 +
>  util/systemd.c         |  77 +++++++++++++++++++++++++++++++++++++
>  5 files changed, 125 insertions(+), 130 deletions(-)
>  create mode 100644 include/qemu/systemd.h
>  create mode 100644 util/systemd.c
> 
> diff --git a/include/qemu/systemd.h b/include/qemu/systemd.h
> new file mode 100644
> index 0000000..e6a877e
> --- /dev/null
> +++ b/include/qemu/systemd.h
> @@ -0,0 +1,26 @@
> +/*
> + * systemd socket activation support
> + *
> + * Copyright 2017 Red Hat, Inc. and/or its affiliates
> + *
> + * Authors:
> + *  Richard W.M. Jones <rjones@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#ifndef QEMU_SYSTEMD_H
> +#define QEMU_SYSTEMD_H 1
> +
> +#define FIRST_SOCKET_ACTIVATION_FD 3 /* defined by systemd ABI */
> +
> +/*
> + * Check if socket activation was requested via use of the
> + * LISTEN_FDS and LISTEN_PID environment variables.
> + *
> + * Returns 0 if no socket activation, or the number of FDs.
> + */
> +unsigned int check_socket_activation(void);
> +
> +#endif
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index e4fede6..f332d30 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -28,6 +28,7 @@
>  #include "qemu/config-file.h"
>  #include "qemu/bswap.h"
>  #include "qemu/log.h"
> +#include "qemu/systemd.h"
>  #include "block/snapshot.h"
>  #include "qapi/util.h"
>  #include "qapi/qmp/qstring.h"
> @@ -474,98 +475,6 @@ static void setup_address_and_port(const char **address, const char **port)
>      }
>  }
>  
> -#define FIRST_SOCKET_ACTIVATION_FD 3 /* defined by systemd ABI */
> -
> -#ifndef _WIN32
> -/*
> - * Check if socket activation was requested via use of the
> - * LISTEN_FDS and LISTEN_PID environment variables.
> - *
> - * Returns 0 if no socket activation, or the number of FDs.
> - */
> -static unsigned int check_socket_activation(void)
> -{
> -    const char *s;
> -    unsigned long pid;
> -    unsigned long nr_fds;
> -    unsigned int i;
> -    int fd;
> -    int err;
> -
> -    s = getenv("LISTEN_PID");
> -    if (s == NULL) {
> -        return 0;
> -    }
> -    err = qemu_strtoul(s, NULL, 10, &pid);
> -    if (err) {
> -        if (verbose) {
> -            fprintf(stderr, "malformed %s environment variable (ignored)\n",
> -                    "LISTEN_PID");
> -        }
> -        return 0;
> -    }
> -    if (pid != getpid()) {
> -        if (verbose) {
> -            fprintf(stderr, "%s was not for us (ignored)\n",
> -                    "LISTEN_PID");
> -        }
> -        return 0;
> -    }
> -
> -    s = getenv("LISTEN_FDS");
> -    if (s == NULL) {
> -        return 0;
> -    }
> -    err = qemu_strtoul(s, NULL, 10, &nr_fds);
> -    if (err) {
> -        if (verbose) {
> -            fprintf(stderr, "malformed %s environment variable (ignored)\n",
> -                    "LISTEN_FDS");
> -        }
> -        return 0;
> -    }
> -    assert(nr_fds <= UINT_MAX);
> -
> -    /* A limitation of current qemu-nbd is that it can only listen on
> -     * a single socket.  When that limitation is lifted, we can change
> -     * this function to allow LISTEN_FDS > 1, and remove the assertion
> -     * in the main function below.
> -     */
> -    if (nr_fds > 1) {
> -        error_report("qemu-nbd does not support socket activation with %s > 1",
> -                     "LISTEN_FDS");
> -        exit(EXIT_FAILURE);
> -    }
> -
> -    /* So these are not passed to any child processes we might start. */
> -    unsetenv("LISTEN_FDS");
> -    unsetenv("LISTEN_PID");
> -
> -    /* So the file descriptors don't leak into child processes. */
> -    for (i = 0; i < nr_fds; ++i) {
> -        fd = FIRST_SOCKET_ACTIVATION_FD + i;
> -        if (fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) {
> -            /* If we cannot set FD_CLOEXEC then it probably means the file
> -             * descriptor is invalid, so socket activation has gone wrong
> -             * and we should exit.
> -             */
> -            error_report("Socket activation failed: "
> -                         "invalid file descriptor fd = %d: %m",
> -                         fd);
> -            exit(EXIT_FAILURE);
> -        }
> -    }
> -
> -    return (unsigned int) nr_fds;
> -}
> -
> -#else /* !_WIN32 */
> -static unsigned int check_socket_activation(void)
> -{
> -    return 0;
> -}
> -#endif
> -
>  /*
>   * Check socket parameters compatibility when socket activation is used.
>   */
> @@ -892,6 +801,13 @@ int main(int argc, char **argv)
>              error_report("%s", err_msg);
>              exit(EXIT_FAILURE);
>          }
> +
> +	/* qemu-nbd can only listen on a single socket.  */
> +	if (socket_activation > 1) {
> +            error_report("qemu-nbd does not support socket activation with %s > 1",
> +                         "LISTEN_FDS");
> +            exit(EXIT_FAILURE);
> +	}
>      }
>  
>      if (tlscredsid) {
> diff --git a/qga/main.c b/qga/main.c
> index 92658bc..284dfbe 100644
> --- a/qga/main.c
> +++ b/qga/main.c
> @@ -29,6 +29,7 @@
>  #include "qemu/bswap.h"
>  #include "qemu/help_option.h"
>  #include "qemu/sockets.h"
> +#include "qemu/systemd.h"
>  #ifdef _WIN32
>  #include "qga/service-win32.h"
>  #include "qga/vss-win32.h"
> @@ -186,37 +187,6 @@ void reopen_fd_to_null(int fd)
>  }
>  #endif
>  
> -/**
> - * get_listen_fd:
> - * @consume: true to prevent future calls from succeeding
> - *
> - * Fetch a listen file descriptor that was passed via systemd socket
> - * activation.  Use @consume to prevent child processes from thinking a file
> - * descriptor was passed.
> - *
> - * Returns: file descriptor or -1 if no fd was passed
> - */
> -static int get_listen_fd(bool consume)
> -{
> -#ifdef _WIN32
> -    return -1; /* no fd passing expected, unsetenv(3) not available */
> -#else
> -    const char *listen_fds = getenv("LISTEN_FDS");
> -    int fd = STDERR_FILENO + 1;
> -
> -    if (!listen_fds || strcmp(listen_fds, "1") != 0) {
> -        return -1;
> -    }
> -
> -    if (consume) {
> -        unsetenv("LISTEN_FDS");
> -    }
> -
> -    qemu_set_cloexec(fd);
> -    return fd;
> -#endif /* !_WIN32 */
> -}
> -
>  static void usage(const char *cmd)
>  {
>      printf(
> @@ -1251,7 +1221,7 @@ static bool check_is_frozen(GAState *s)
>      return false;
>  }
>  
> -static int run_agent(GAState *s, GAConfig *config)
> +static int run_agent(GAState *s, GAConfig *config, int socket_activation)
>  {
>      ga_state = s;
>  
> @@ -1333,7 +1303,7 @@ static int run_agent(GAState *s, GAConfig *config)
>      s->main_loop = g_main_loop_new(NULL, false);
>  
>      if (!channel_init(ga_state, config->method, config->channel_path,
> -                      get_listen_fd(true))) {
> +                      socket_activation ? FIRST_SOCKET_ACTIVATION_FD : -1)) {
>          g_critical("failed to initialize guest agent channel");
>          return EXIT_FAILURE;
>      }
> @@ -1357,7 +1327,7 @@ int main(int argc, char **argv)
>      int ret = EXIT_SUCCESS;
>      GAState *s = g_new0(GAState, 1);
>      GAConfig *config = g_new0(GAConfig, 1);
> -    int listen_fd;
> +    int socket_activation;
>  
>      config->log_level = G_LOG_LEVEL_ERROR | G_LOG_LEVEL_CRITICAL;
>  
> @@ -1379,8 +1349,13 @@ int main(int argc, char **argv)
>          config->method = g_strdup("virtio-serial");
>      }
>  
> -    listen_fd = get_listen_fd(false);
> -    if (listen_fd >= 0) {
> +    socket_activation = check_socket_activation();
> +    if (socket_activation > 1) {
> +        g_critical("qemu-ga only supports listening on one socket");
> +        ret = EXIT_FAILURE;
> +        goto end;
> +    }
> +    if (socket_activation) {
>          SocketAddress *addr;
>  
>          g_free(config->method);
> @@ -1388,7 +1363,7 @@ int main(int argc, char **argv)
>          config->method = NULL;
>          config->channel_path = NULL;
>  
> -        addr = socket_local_address(listen_fd, NULL);
> +        addr = socket_local_address(FIRST_SOCKET_ACTIVATION_FD , NULL);
>          if (addr) {
>              if (addr->type == SOCKET_ADDRESS_KIND_UNIX) {
>                  config->method = g_strdup("unix-listen");
> @@ -1433,7 +1408,7 @@ int main(int argc, char **argv)
>          goto end;
>      }
>  
> -    ret = run_agent(s, config);
> +    ret = run_agent(s, config, socket_activation);
>  
>  end:
>      if (s->command_state) {
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index 06366b5..c6205eb 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -42,3 +42,4 @@ util-obj-y += log.o
>  util-obj-y += qdist.o
>  util-obj-y += qht.o
>  util-obj-y += range.o
> +util-obj-y += systemd.o
> diff --git a/util/systemd.c b/util/systemd.c
> new file mode 100644
> index 0000000..bf7a4ef
> --- /dev/null
> +++ b/util/systemd.c
> @@ -0,0 +1,77 @@
> +/*
> + * systemd socket activation support
> + *
> + * Copyright 2017 Red Hat, Inc. and/or its affiliates
> + *
> + * Authors:
> + *  Richard W.M. Jones <rjones@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/systemd.h"
> +#include "qemu/cutils.h"
> +#include "qemu/error-report.h"
> +
> +#ifndef _WIN32
> +unsigned int check_socket_activation(void)
> +{
> +    const char *s;
> +    unsigned long pid;
> +    unsigned long nr_fds;
> +    unsigned int i;
> +    int fd;
> +    int err;
> +
> +    s = getenv("LISTEN_PID");
> +    if (s == NULL) {
> +        return 0;
> +    }
> +    err = qemu_strtoul(s, NULL, 10, &pid);
> +    if (err) {
> +        return 0;
> +    }
> +    if (pid != getpid()) {
> +        return 0;
> +    }
> +
> +    s = getenv("LISTEN_FDS");
> +    if (s == NULL) {
> +        return 0;
> +    }
> +    err = qemu_strtoul(s, NULL, 10, &nr_fds);
> +    if (err) {
> +        return 0;
> +    }
> +    assert(nr_fds <= UINT_MAX);
> +
> +    /* So these are not passed to any child processes we might start. */
> +    unsetenv("LISTEN_FDS");
> +    unsetenv("LISTEN_PID");
> +
> +    /* So the file descriptors don't leak into child processes. */
> +    for (i = 0; i < nr_fds; ++i) {
> +        fd = FIRST_SOCKET_ACTIVATION_FD + i;
> +        if (fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) {
> +            /* If we cannot set FD_CLOEXEC then it probably means the file
> +             * descriptor is invalid, so socket activation has gone wrong
> +             * and we should exit.
> +             */
> +            error_report("Socket activation failed: "
> +                         "invalid file descriptor fd = %d: %m",
> +                         fd);
> +            exit(EXIT_FAILURE);
> +        }
> +    }
> +
> +    return (unsigned int) nr_fds;
> +}
> +
> +#else /* !_WIN32 */
> +static unsigned int check_socket_activation(void)
> +{
> +    return 0;
> +}
> +#endif
> -- 
> 2.9.3

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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