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

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Date:	Tue, 06 Aug 2013 13:56:41 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	security@...nel.org, oss-security@...ts.openwall.com,
	Petr Matousek <pmatouse@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] userns: unshare_userns(&cred) should not populate cred on failure

Oleg Nesterov <oleg@...hat.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@...ssion.com>

> Cc: stable@...r.kernel.org
> Signed-off-by: Oleg Nesterov <oleg@...hat.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)
--
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