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

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

[Oleg Nesterov]

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.

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)
-- 
1.5.5.1

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

[Andy Lutomirski]

On Tue, Aug 6, 2013 at 10:38 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> 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.
>
> 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)
> --
> 1.5.5.1
>
>

Reviewed-by: Andy Lutomirski <luto@amacapital.net>


-- 
Andy Lutomirski
AMA Capital Management, LLC

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

[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)