netdev - Re: [PATCH] xfrm: policy: Fix possible user after free in __xfrm_policy

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Date:   Thu, 28 Feb 2019 12:12:01 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Yue Haibing <yuehaibing@...wei.com>
Cc:     steffen.klassert@...unet.com, davem@...emloft.net,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Fan Du <fan.du@...driver.com>
Subject: Re: [PATCH] xfrm: policy: Fix possible user after free in
 __xfrm_policy_unlink

On Thu, Feb 28, 2019 at 11:16:23AM +0800, Yue Haibing wrote:
> 
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index 8d1a898..b27eb742 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -316,6 +316,8 @@ static void xfrm_policy_timer(struct timer_list *t)
>  		goto out;
>  
>  	dir = xfrm_policy_id2dir(xp->index);
> +	if (dir >= XFRM_POLICY_MAX * 2)
> +		dir = dir & XFRM_POLICY_MAX;

This is still wrong.  We shouldn't be allowing bogus policies
to be in the system at all.

I have digged deeper and the problem was introduced by:

commit e682adf021be796940be6cc10c07be7f7398c220
Author: Fan Du <fan.du@...driver.com>
Date:   Thu Nov 7 17:47:48 2013 +0800

    xfrm: Try to honor policy index if it's supplied by user

Where the check for the user-supplied index is simply wrong in
verify_newpolicy_info.  So please fix it there.

Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt