Re: [PATCH] tools/xenstored: Don't crash xenstored when Live-Update is cancelled

[Juergen Gross <jgross@xxxxxxxx>]

On 17.06.21 19:38, Julien Grall wrote:
> From: Julien GralL <jgrall@xxxxxxxxxx>
>
> As Live-Update is asynchronous, it is possible to receive a request to
> cancel it (either on the same connection or from a different one).
>
> Currently, this will crash xenstored because do_lu_start() assumes
> lu_status will be valid. This is not the case when Live-Update has been
> cancelled. This will result to dereference a NULL pointer and
> crash Xenstored.
>
> Rework do_lu_start() to check if lu_status is NULL and return an
> error in this case.
>
> Fixes: af216a99fb ("tools/xenstore: add the basic framework for doing the live 
> update")
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
>
> ----
>
> This is currently based on top of:
>
> https://lore.kernel.org/xen-devel/20210616144324.31652-1-julien@xxxxxxx
>
> This can be re-ordered if necessary.
> ---
>   tools/xenstore/xenstored_control.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/tools/xenstore/xenstored_control.c 
> b/tools/xenstore/xenstored_control.c
> index a045f102a420..37a3d39f20b5 100644
> --- a/tools/xenstore/xenstored_control.c
> +++ b/tools/xenstore/xenstored_control.c
> @@ -696,7 +696,18 @@ static bool do_lu_start(struct delayed_request *req)
>         time_t now = time(NULL);
>         const char *ret;
>         struct buffered_data *saved_in;
> -       struct connection *conn = lu_status->conn;
> +       struct connection *conn = req->data;
> +
> +       /*
> +        * Cancellation may have been requested asynchronously. In this
> +        * case, lu_status will be NULL.
> +        */
> +       if (!lu_status) {
> +               ret = "Cancellation was requested";
> +               conn = req->data;
This will set conn to the same value it already has.


Other than that:

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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