linux-kernel - Re: [PATCH] kref: Avoid null pointer dereference after WARN

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Message-ID: <20170627070626.GH29909@kroah.com>
Date:   Tue, 27 Jun 2017 09:06:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Daniel Micay <danielmicay@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kref: Avoid null pointer dereference after WARN

On Mon, Jun 26, 2017 at 08:52:15PM -0700, Kees Cook wrote:
> From: Daniel Micay <danielmicay@...il.com>
> 
> The WARN_ON() checking for a NULL release pointer should be a BUG()
> since continuing with a NULL release pointer will lead to a NULL
> pointer dereference anyway.
> 
> The kref_put() case is extracted from PaX, and Kees Cook noted it should
> be extended to the other two cases.
> 
> Signed-off-by: Daniel Micay <danielmicay@...il.com>
> [kees: clarify commit log]
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  include/linux/kref.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/kref.h b/include/linux/kref.h
> index f4156f88f557..82a2c225eae3 100644
> --- a/include/linux/kref.h
> +++ b/include/linux/kref.h
> @@ -66,7 +66,7 @@ static inline void kref_get(struct kref *kref)
>   */
>  static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
>  {
> -	WARN_ON(release == NULL);
> +	BUG_ON(release == NULL);

I remember one complaint was that WARN_ON was "huge" and this bloated
the kernel code a lot.  But then that got fixed up.  Is BUG_ON going to
cause the same complaint again?

thanks,

greg k-h