Re: [PATCH v4 1/3] qio: add support for SO_PEERCRED for socket channel

[Daniel P . Berrangé]

On Mon, Mar 18, 2024 at 04:12:14PM +0100, Anthony Harivel wrote:
> The function qio_channel_get_peercred() returns a pointer to the
> credentials of the peer process connected to this socket.
> 
> This credentials structure is defined in <sys/socket.h> as follows:
> 
> struct ucred {
>       pid_t pid;    /* Process ID of the sending process */
>       uid_t uid;    /* User ID of the sending process */
>       gid_t gid;    /* Group ID of the sending process */
> };
> 
> The use of this function is possible only for connected AF_UNIX stream
> sockets and for AF_UNIX stream and datagram socket pairs.
> 
> On platform other than Linux, the function return 0.
> 
> Signed-off-by: Anthony Harivel <aharivel@redhat.com>
> ---
>  include/io/channel.h | 21 +++++++++++++++++++++
>  io/channel-socket.c  | 24 ++++++++++++++++++++++++
>  io/channel.c         | 12 ++++++++++++
>  3 files changed, 57 insertions(+)
> 
> diff --git a/include/io/channel.h b/include/io/channel.h
> index 7986c49c713a..01ad7bd7e430 100644
> --- a/include/io/channel.h
> +++ b/include/io/channel.h
> @@ -160,6 +160,9 @@ struct QIOChannelClass {
>                                    void *opaque);
>      int (*io_flush)(QIOChannel *ioc,
>                      Error **errp);
> +    void (*io_peerpid)(QIOChannel *ioc,
> +                       unsigned int *pid,
> +                       Error **errp);
>  };
>  
>  /* General I/O handling functions */
> @@ -981,4 +984,22 @@ int coroutine_mixed_fn 
> qio_channel_writev_full_all(QIOChannel *ioc,
>  int qio_channel_flush(QIOChannel *ioc,
>                        Error **errp);
>  
> +/**
> + * qio_channel_get_peercred:
> + * @ioc: the channel object
> + * @pid: pointer to pid
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Returns the pid of the peer process connected to this socket.
> + *
> + * The use of this function is possible only for connected
> + * AF_UNIX stream sockets and for AF_UNIX stream and datagram
> + * socket pairs on Linux.
> + * Return an error with pid -1 for the non-Linux OS.
> + *
> + */
> +void qio_channel_get_peerpid(QIOChannel *ioc,
> +                             unsigned int *pid,
> +                             Error **errp);
> +
>  #endif /* QIO_CHANNEL_H */
> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index 3a899b060858..fcff92ecc151 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -841,6 +841,29 @@ qio_channel_socket_set_cork(QIOChannel *ioc,
>      socket_set_cork(sioc->fd, v);
>  }
>  
> +static void
> +qio_channel_socket_get_peerpid(QIOChannel *ioc,
> +                               unsigned int *pid,
> +                               Error **errp)
> +{
> +#ifdef CONFIG_LINUX
> +    QIOChannelSocket *sioc = QIO_CHANNEL_SOCKET(ioc);
> +    Error *err = NULL;
> +    socklen_t len = sizeof(struct ucred);
> +
> +    struct ucred cred;
> +    if (getsockopt(sioc->fd,
> +               SOL_SOCKET, SO_PEERCRED,
> +               &cred, &len) == -1) {

Set '*pid = -1'

> +        error_setg_errno(&err, errno, "Unable to get peer credentials");
> +        error_propagate(errp, err);

and 'return;' here, since accessing 'cred.pid' below
is undefined behaviour if getsockopt failed.

> +    }
> +    *pid = (unsigned int)cred.pid;
> +#else
> +    error_setg(errp, "Unsupported feature");
> +    *pid = -1;
> +#endif
> +}
>  
>  static int
>  qio_channel_socket_close(QIOChannel *ioc,
> @@ -938,6 +961,7 @@ static void qio_channel_socket_class_init(ObjectClass 
> *klass,
>  #ifdef QEMU_MSG_ZEROCOPY
>      ioc_klass->io_flush = qio_channel_socket_flush;
>  #endif
> +    ioc_klass->io_peerpid = qio_channel_socket_get_peerpid;
>  }
>  
>  static const TypeInfo qio_channel_socket_info = {
> diff --git a/io/channel.c b/io/channel.c
> index a1f12f8e9096..777989bc9a81 100644
> --- a/io/channel.c
> +++ b/io/channel.c
> @@ -548,6 +548,18 @@ void qio_channel_set_cork(QIOChannel *ioc,
>      }
>  }
>  
> +void qio_channel_get_peerpid(QIOChannel *ioc,
> +                             unsigned int *pid,
> +                             Error **errp)
> +{
> +    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
> +
> +    if (!klass->io_peerpid) {
> +        error_setg(errp, "Channel does not support peer pid");
> +        return;
> +    }
> +    klass->io_peerpid(ioc, pid, errp);
> +}
>  
>  off_t qio_channel_io_seek(QIOChannel *ioc,
>                            off_t offset,
> -- 
> 2.44.0
> 

With regards,
Daniel
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