linux-kernel - Re: [PATCH] selinux: Handle NULL return from selinux_inode in inode_security

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Message-ID: <CAEjxPJ4ewk2E0NjYa=B3GA9jh2+rDbipnhRuWUcJLAUcxG2LtA@mail.gmail.com>
Date: Thu, 16 Jan 2025 15:37:58 -0500
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Ingyu Jang <ingyujang25@...il.com>
Cc: Paul Moore <paul@...l-moore.com>, Ondrej Mosnacek <omosnace@...hat.com>, selinux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selinux: Handle NULL return from selinux_inode in inode_security_rcu

On Thu, Jan 16, 2025 at 2:55 PM Ingyu Jang <ingyujang25@...il.com> wrote:
>
> The 'selinux_inode' function may return NULL if 'inode->i_security' is
> uninitialized or if 'inode->i_security' is NULL.
> Previously, this scenario was not explicitly handled in
> 'inode_security_rcu', which might lead to NULL Pointer dereference.
>
> This patch modifies 'inode_security_rcu' to call 'selinux_inode' and
> check its return value.
> If 'selinux_inode' returns NULL, '-EACCES' is returned to ensure
> consistent error handling.
>
> Furthermore, analysis confirmed that all current usages of
> 'inode_security_rcu' check the return value using 'IS_ERR', ensuring
> compatibility with this change.
>
> Signed-off-by: Ingyu Jang <ingyujang25@...il.com>

Do you have an actual example where this is currently possible if
SELinux is enabled?
It shouldn't be possible, so that would be a kernel bug that should be fixed.

> ---
>  security/selinux/hooks.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 171dd7fceac5..61c9191bafbe 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -310,11 +310,17 @@ static struct inode_security_struct *inode_security_novalidate(struct inode *ino
>  static struct inode_security_struct *inode_security_rcu(struct inode *inode, bool rcu)
>  {
>         int error;
> +       struct inode_security_struct *isec;
>
>         error = __inode_security_revalidate(inode, NULL, !rcu);
>         if (error)
>                 return ERR_PTR(error);
> -       return selinux_inode(inode);
> +
> +       isec = selinux_inode(inode);
> +       if (!isec)
> +               return ERR_PTR(-EACCES);
> +
> +       return isec;
>  }
>
>  /*
> --
> 2.34.1
>