Re: [PATCH v2 1/3] win32: add qemu_close_socket_osfhandle()

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Mar 20, 2023 at 05:46:01PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Mon, Mar 20, 2023 at 5:42 PM Daniel P. Berrangé <berrange@redhat.com>
> wrote:
> 
> > On Mon, Mar 20, 2023 at 05:36:41PM +0400, marcandre.lureau@redhat.com
> > wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > Close the given file descriptor, but returns the underlying SOCKET.
> > >
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >  include/sysemu/os-win32.h | 15 ++++++--
> > >  util/oslib-win32.c        | 75 +++++++++++++++++++++------------------
> > >  2 files changed, 53 insertions(+), 37 deletions(-)
> > >
> > > diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
> > > index e2849f88ab..15c296e0eb 100644
> > > --- a/include/sysemu/os-win32.h
> > > +++ b/include/sysemu/os-win32.h
> > > @@ -171,10 +171,21 @@ bool qemu_socket_select(int sockfd, WSAEVENT
> > hEventObject,
> > >
> > >  bool qemu_socket_unselect(int sockfd, Error **errp);
> > >
> > > -/* We wrap all the sockets functions so that we can
> > > - * set errno based on WSAGetLastError()
> > > +/* We wrap all the sockets functions so that we can set errno based on
> > > + * WSAGetLastError(), and use file-descriptors instead of SOCKET.
> > >   */
> > >
> > > +/*
> > > + * qemu_close_socket_osfhandle:
> > > + * @fd: a file descriptor associated with a SOCKET
> > > + *
> > > + * Close only the C run-time file descriptor, leave the SOCKET opened.
> > > + *
> > > + * Returns zero on success. On error, -1 is returned, and errno is set
> > to
> > > + * indicate the error.
> > > + */
> > > +int qemu_close_socket_osfhandle(int fd);
> > > +
> > >  #undef close
> > >  #define close qemu_close_wrap
> > >  int qemu_close_wrap(int fd);
> > > diff --git a/util/oslib-win32.c b/util/oslib-win32.c
> > > index 16f8a67f7e..a98638729a 100644
> > > --- a/util/oslib-win32.c
> > > +++ b/util/oslib-win32.c
> > > @@ -479,40 +479,27 @@ int qemu_bind_wrap(int sockfd, const struct
> > sockaddr *addr,
> > >      return ret;
> > >  }
> > >
> > > -
> > >  #undef close
> > > -int qemu_close_wrap(int fd)
> > > +int qemu_close_socket_osfhandle(int fd)
> > >  {
> > > -    int ret;
> > > +    SOCKET s = _get_osfhandle(fd);
> > >      DWORD flags = 0;
> > > -    SOCKET s = INVALID_SOCKET;
> > > -
> > > -    if (fd_is_socket(fd)) {
> > > -        s = _get_osfhandle(fd);
> > > -
> > > -        /*
> > > -         * If we were to just call _close on the descriptor, it would
> > close the
> > > -         * HANDLE, but it wouldn't free any of the resources associated
> > to the
> > > -         * SOCKET, and we can't call _close after calling closesocket,
> > because
> > > -         * closesocket has already closed the HANDLE, and _close would
> > attempt to
> > > -         * close the HANDLE again, resulting in a double free. We can
> > however
> > > -         * protect the HANDLE from actually being closed long enough to
> > close the
> > > -         * file descriptor, then close the socket itself.
> > > -         */
> > > -        if (!GetHandleInformation((HANDLE)s, &flags)) {
> > > -            errno = EACCES;
> > > -            return -1;
> > > -        }
> > >
> > > -        if (!SetHandleInformation((HANDLE)s,
> > HANDLE_FLAG_PROTECT_FROM_CLOSE, HANDLE_FLAG_PROTECT_FROM_CLOSE)) {
> > > -            errno = EACCES;
> > > -            return -1;
> > > -        }
> > > +    /*
> > > +     * If we were to just call _close on the descriptor, it would close
> > the
> > > +     * HANDLE, but it wouldn't free any of the resources associated to
> > the
> > > +     * SOCKET, and we can't call _close after calling closesocket,
> > because
> > > +     * closesocket has already closed the HANDLE, and _close would
> > attempt to
> > > +     * close the HANDLE again, resulting in a double free. We can
> > however
> > > +     * protect the HANDLE from actually being closed long enough to
> > close the
> > > +     * file descriptor, then close the socket itself.
> > > +     */
> > > +    if (!GetHandleInformation((HANDLE)s, &flags)) {
> > > +        errno = EACCES;
> > > +        return -1;
> > >      }
> > >
> > > -    ret = close(fd);
> > > -
> > > -    if (s != INVALID_SOCKET && !SetHandleInformation((HANDLE)s, flags,
> > flags)) {
> > > +    if (!SetHandleInformation((HANDLE)s,
> > HANDLE_FLAG_PROTECT_FROM_CLOSE, HANDLE_FLAG_PROTECT_FROM_CLOSE)) {
> > >          errno = EACCES;
> > >          return -1;
> > >      }
> > > @@ -521,15 +508,33 @@ int qemu_close_wrap(int fd)
> > >       * close() returns EBADF since we PROTECT_FROM_CLOSE the underlying
> > handle,
> > >       * but the FD is actually freed
> > >       */
> > > -    if (ret < 0 && (s == INVALID_SOCKET || errno != EBADF)) {
> > > -        return ret;
> > > +    if (close(fd) < 0 && errno != EBADF) {
> > > +        return -1;
> > >      }
> > >
> > > -    if (s != INVALID_SOCKET) {
> > > -        ret = closesocket(s);
> > > -        if (ret < 0) {
> > > -            errno = socket_error();
> > > -        }
> > > +    if (!SetHandleInformation((HANDLE)s, flags, flags)) {
> > > +        errno = EACCES;
> > > +        return -1;
> > > +    }
> > > +
> > > +    return 0;
> > > +}
> > > +
> > > +int qemu_close_wrap(int fd)
> > > +{
> > > +    SOCKET s = INVALID_SOCKET;
> > > +    int ret = -1;
> > > +
> > > +    if (!fd_is_socket(fd)) {
> > > +        return close(fd);
> > > +    }
> > > +
> > > +    s = _get_osfhandle(fd);
> > > +    qemu_close_socket_osfhandle(fd);
> > > +
> > > +    ret = closesocket(s);
> > > +    if (ret < 0) {
> > > +        errno = socket_error();
> > >      }
> >
> > Shouldn't the closesocket() and return check be wrapped in
> >
> >    if (s != INVALID_SOCKET) { .... }
> >
> >
> We shouldn't get there since fd_is_socket().

Oh right, yes,  fd_is_socket() will evaluate false if the 'fd' is
invalid. eg qemu_clsoe_wrap(-1)

> > as the old code had that conditional invokation of closesocket() ?
> >
> 
> The v1 code could actually leak a SOCKET. This version should be a bit
> better, if the FD is already closed for example, we still close the SOCKET.
> 
> Open to ideas to improve it.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

With regards,
Daniel
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