[CRIU] [PATCH v2 2/2] unix: don't drop the path on unix sockets if they don't exist

[Pavel Emelyanov]

> @@ -962,8 +959,53 @@ static int bind_unix_sk(int sk, struct unix_sk_info *ui)
>  		ret = bind(sk, (struct sockaddr *)&addr,
>  				sizeof(addr.sun_family) + ui->ue->name.len);
>  		if (ret < 0) {
> -			pr_perror("Can't bind socket");
> -			goto done;
> +			if (ui->ue->has_deleted && ui->ue->deleted && errno == EADDRINUSE) {
> +				char temp[PATH_MAX];
> +
> +				pr_info("found duplicate unix socket bound at %s\n", addr.sun_path);
> +
> +				ret = snprintf(temp, sizeof(temp), "%s-%s-%d", addr.sun_path, "criu-temp", getpid());
> +				/* this shouldn't happen, since sun_addr is only 108 chars long */
> +				if (ret < 0 || ret >= sizeof(temp)) {
> +					pr_err("snprintf of %s failed?\n", addr.sun_path);
> +					goto done;
> +				}
> +
> +				ret = rename(addr.sun_path, temp);
> +				if (ret < 0) {
> +					pr_perror("couldn't move socket for binding");
> +					goto done;
> +				}
> +
> +				ret = bind(sk, (struct sockaddr *)&addr,
> +						sizeof(addr.sun_family) + ui->ue->name.len);
> +				if (ret < 0) {
> +					pr_perror("Can't bind socket after move");
> +					goto done;
> +				}
> +
> +				ret = unlink(addr.sun_path);

This unlink seems redundant, the rename below should unlink it.

> +				if (ret < 0) {
> +					pr_perror("Can't unlink socket after bind");
> +					goto done;
> +				}
> +
> +				ret = rename(temp, addr.sun_path);
> +				if (ret < 0) {
> +					pr_perror("couldn't move socket back");
> +					goto done;
> +				}
> +
> +				/* we've handled the deleted-ness of this
> +				 * socket and we don't want to delete it later
> +				 * since it's not /this/ socket.
> +				 */
> +				ui->ue->deleted = false;
> +
> +			} else {
> +				pr_perror("Can't bind socket");
> +				goto done;
> +			}
>  		}
>  
>  		if (*ui->name && ui->ue->file_perms) {
> @@ -1225,6 +1267,11 @@ out:
>  	if (restore_socket_opts(sk, ui->ue->opts))
>  		return -1;
>  
> +	if (ui->ue->deleted && unlink((char *)ui->ue->name.data) < 0) {

I worry that we do this move/bind/unlink/move logic in bind_unix_sk(), which is
called in several places, but remove the deleted name only here. Is this safe?

> +		pr_perror("failed to unlink %s\n", ui->ue->name.data);
> +		return -1;
> +	}
> +
>  	return sk;
>  }
>  
> diff --git a/images/sk-unix.proto b/images/sk-unix.proto
> index aa2bcf7..75ec3bf 100644
> --- a/images/sk-unix.proto
> +++ b/images/sk-unix.proto
> @@ -45,4 +45,5 @@ message unix_sk_entry {
>  	 * Relative socket name may have prefix.
>  	 */
>  	optional string			name_dir	= 14;
> +	optional bool			deleted		= 15;
>  }
>