Re: [PATCH 2/2] migration: Fix error handling after dup in file migration

[Peter Xu]

On Tue, Mar 12, 2024 at 09:57:58AM +0000, Daniel P. Berrangé wrote:
> On Mon, Mar 11, 2024 at 08:33:35PM -0300, Fabiano Rosas wrote:
> > The file migration code was allowing a possible -1 from a failed call
> > to dup() to propagate into the new QIOFileChannel::fd before checking
> > for validity. Coverity doesn't like that, possibly due to the the
> > lseek(-1, ...) call that would ensue before returning from the channel
> > creation routine.
> > 
> > Use the newly introduced qio_channel_file_dupfd() to properly check
> > the return of dup() before proceeding.
> > 
> > Fixes: CID 1539961
> > Fixes: CID 1539965
> > Fixes: CID 1539960
> > Fixes: 2dd7ee7a51 ("migration/multifd: Add incoming QIOChannelFile support")
> > Fixes: decdc76772 ("migration/multifd: Add mapped-ram support to fd: URI")
> > Reported-by: Peter Maydell <peter.maydell@linaro.org>
> > Signed-off-by: Fabiano Rosas <farosas@suse.de>
> > ---
> >  migration/fd.c   |  9 ++++-----
> >  migration/file.c | 14 +++++++-------
> >  2 files changed, 11 insertions(+), 12 deletions(-)
> > 
> > diff --git a/migration/fd.c b/migration/fd.c
> > index d4ae72d132..4e2a63a73d 100644
> > --- a/migration/fd.c
> > +++ b/migration/fd.c
> > @@ -80,6 +80,7 @@ static gboolean fd_accept_incoming_migration(QIOChannel 
> > *ioc,
> >  void fd_start_incoming_migration(const char *fdname, Error **errp)
> >  {
> >      QIOChannel *ioc;
> > +    QIOChannelFile *fioc;
> >      int fd = monitor_fd_param(monitor_cur(), fdname, errp);
> >      if (fd == -1) {
> >          return;
> > @@ -103,15 +104,13 @@ void fd_start_incoming_migration(const char *fdname, 
> > Error **errp)
> >          int channels = migrate_multifd_channels();
> >  
> >          while (channels--) {
> > -            ioc = QIO_CHANNEL(qio_channel_file_new_fd(dup(fd)));
> > -
> > -            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
> > -                error_setg(errp, "Failed to duplicate fd %d", fd);
> > +            fioc = qio_channel_file_new_dupfd(fd, errp);
> > +            if (!fioc) {
> >                  return;
> >              }
> >  
> >              qio_channel_set_name(ioc, "migration-fd-incoming");
> > -            qio_channel_add_watch_full(ioc, G_IO_IN,
> > +            qio_channel_add_watch_full(QIO_CHANNEL(fioc), G_IO_IN,
> >                                         fd_accept_incoming_migration,
> >                                         NULL, NULL,
> >                                         
> > g_main_context_get_thread_default());
> 
> Nothing is free'ing the already created channels, if this while()
> loop fails on the 2nd or later iterations.
> 
> > diff --git a/migration/file.c b/migration/file.c
> > index 164b079966..d458f48269 100644
> > --- a/migration/file.c
> > +++ b/migration/file.c
> > @@ -58,12 +58,13 @@ bool file_send_channel_create(gpointer opaque, Error 
> > **errp)
> >      int fd = fd_args_get_fd();
> >  
> >      if (fd && fd != -1) {
> > -        ioc = qio_channel_file_new_fd(dup(fd));
> > +        ioc = qio_channel_file_new_dupfd(fd, errp);
> >      } else {
> >          ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, 
> > errp);
> > -        if (!ioc) {
> > -            goto out;
> > -        }
> > +    }
> > +
> > +    if (!ioc) {
> > +        goto out;
> >      }
> >  
> >      multifd_channel_connect(opaque, QIO_CHANNEL(ioc));
> > @@ -147,10 +148,9 @@ void file_start_incoming_migration(FileMigrationArgs 
> > *file_args, Error **errp)
> >                                     NULL, NULL,
> >                                     g_main_context_get_thread_default());
> >  
> > -        fioc = qio_channel_file_new_fd(dup(fioc->fd));
> > +        fioc = qio_channel_file_new_dupfd(fioc->fd, errp);
> >  
> > -        if (!fioc || fioc->fd == -1) {
> > -            error_setg(errp, "Error creating migration incoming channel");
> > +        if (!fioc) {
> >              break;
> >          }
> >      } while (++i < channels);
> 
> Again, nothing is free'ing when the loops fails on 2nd or later
> iterations.

For this one, I think it constantly leak one IOC even if no failure
triggers..

> 
> So a weak
> 
>   Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> 
> on the basis that it fixes the bugs that it claims to fix, but there
> are more bugs that still need fixing here.

For the other issue, Fabiano - I think there's one easy way to workaround
and avoid bothering with "how to remove a registered IO watch" is we create
the IOCs in a loop first, register the IO watches only if all succeeded.

I'll queue the series first to fix the reported issue.

Thanks,

-- 
Peter Xu