Re: [PATCH 1/1] userns: unshare_userns(&cred) should not populate cred on failure

[ebiederm () xmission com (Eric W. Biederman)]

Oleg Nesterov <oleg () redhat com> writes:

> unshare_userns(new_cred) does *new_cred = prepare_creds() before
> create_user_ns() which can fail. However, the caller expects that
> it doesn't need to take care of new_cred if unshare_userns() fails.
>
> We could change the single caller, sys_unshare(), but I think it
> would be more clean to avoid the side effects on failure, so with
> this patch unshare_userns() does put_cred() itself and initializes
> *new_cred only if create_user_ns() succeeeds.

Doh!

Reviewed-by: "Eric W. Biederman" <ebiederm () xmission com>

> Cc: stable () vger kernel org
> Signed-off-by: Oleg Nesterov <oleg () redhat com>
> ---
>  kernel/user_namespace.c |   13 +++++++++----
>  1 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index d8c30db..6e50a44 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -105,16 +105,21 @@ int create_user_ns(struct cred *new)
>  int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
>  {
>       struct cred *cred;
> +     int err = -ENOMEM;
>  
>       if (!(unshare_flags & CLONE_NEWUSER))
>               return 0;
>  
>       cred = prepare_creds();
> -     if (!cred)
> -             return -ENOMEM;
> +     if (cred) {
> +             err = create_user_ns(cred);
> +             if (err)
> +                     put_cred(cred);
> +             else
> +                     *new_cred = cred;
> +     }
>  
> -     *new_cred = cred;
> -     return create_user_ns(cred);
> +     return err;
>  }
>  
>  void free_user_ns(struct user_namespace *ns)