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Re: [PATCH] vhost-user-scsi: avoid unlink(NULL) with fd passing


From: Peter Maydell
Subject: Re: [PATCH] vhost-user-scsi: avoid unlink(NULL) with fd passing
Date: Thu, 12 May 2022 16:57:13 +0100

On Wed, 27 Apr 2022 at 11:04, Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> Commit 747421e949fc1eb3ba66b5fcccdb7ba051918241 ("Implements Backend
> Program conventions for vhost-user-scsi") introduced fd-passing support
> as part of implementing the vhost-user backend program conventions.
>
> When fd passing is used the UNIX domain socket path is NULL and we must
> not call unlink(2).
>
> Fixes: Coverity CID 1488353
> Fixes: 747421e949fc1eb3ba66b5fcccdb7ba051918241 ("Implements Backend Program 
> conventions for vhost-user-scsi")
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  contrib/vhost-user-scsi/vhost-user-scsi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/contrib/vhost-user-scsi/vhost-user-scsi.c 
> b/contrib/vhost-user-scsi/vhost-user-scsi.c
> index b2c0f98253..08335d4b2b 100644
> --- a/contrib/vhost-user-scsi/vhost-user-scsi.c
> +++ b/contrib/vhost-user-scsi/vhost-user-scsi.c
> @@ -433,7 +433,9 @@ out:
>      if (vdev_scsi) {
>          g_main_loop_unref(vdev_scsi->loop);
>          g_free(vdev_scsi);
> -        unlink(opt_socket_path);
> +        if (opt_socket_path) {
> +            unlink(opt_socket_path);
> +        }
>      }

Shouldn't this check-and-unlink be one level up, outside the
"if (vdev_scsi)" ? There are error exit paths which get us to
the 'out:' label where we have called unix_sock_new() but
not yet done the g_new0() of vdev_scsi(). The only thing
that needs to be guarded by "if (vdev_scsi)" is the
g_main_loop_unref() (the g_free of vdev_scsi itself could
be inside or outside, since g_free(NULL) is a nop).

thanks
-- PMM



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