Re: [Qemu-trivial] [Qemu-devel] [PATCH v2] qemu-sockets: do not test path with access() before unlinking

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> Using access() is a time-of-check/time-of-use race condition.  It is
> okay to use them to provide better error messages, but that is pretty
> much it.
>
> This is not one such case; on the other hand, access() *will* skip
> unlink() for a non-existent path, so ignore ENOENT return values from
> the unlink() system call.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  util/qemu-sockets.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
> index 9142917..de9145a 100644
> --- a/util/qemu-sockets.c
> +++ b/util/qemu-sockets.c
> @@ -751,8 +751,7 @@ int unix_listen_opts(QemuOpts *opts, Error **errp)
>          qemu_opt_set(opts, "path", un.sun_path, &error_abort);
>      }
>  
> -    if ((access(un.sun_path, F_OK) == 0) &&
> -        unlink(un.sun_path) < 0) {
> +    if (unlink(un.sun_path) < 0 && errno != ENOENT) {
>          error_setg_errno(errp, errno,
>                           "Failed to unlink socket %s", un.sun_path);
>          goto err;

Reviewed-by: Markus Armbruster <armbru@redhat.com>