linux-kernel - Re: [PATCH] net: key: af_key: Fix possible null-pointer dereferences in pfkey_send_policy

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Message-ID: <20190726094514.GD14601@gauss3.secunet.de>
Date:   Fri, 26 Jul 2019 11:45:14 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
CC:     <herbert@...dor.apana.org.au>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: key: af_key: Fix possible null-pointer dereferences
 in pfkey_send_policy_notify()

On Wed, Jul 24, 2019 at 05:35:09PM +0800, Jia-Ju Bai wrote:
> In pfkey_send_policy_notify(), there is an if statement on line 3081 to
> check whether xp is NULL:
>     if (xp && xp->type != XFRM_POLICY_TYPE_MAIN)
> 
> When xp is NULL, it is used by key_notify_policy() on line 3090:
>     key_notify_policy(xp, ...)
>         pfkey_xfrm_policy2msg_prep(xp) -- line 2211
>             pfkey_xfrm_policy2msg_size(xp) -- line 2046
>                 for (i=0; i<xp->xfrm_nr; i++) -- line 2026
>                 t = xp->xfrm_vec + i; -- line 2027
>     key_notify_policy(xp, ...)
>         xp_net(xp) -- line 2231
>             return read_pnet(&xp->xp_net); -- line 534

Please don't quote random code lines, explain the
problem instead.

> 
> Thus, possible null-pointer dereferences may occur.
> 
> To fix these bugs, xp is checked before calling key_notify_policy().
> 
> These bugs are found by a static analysis tool STCheck written by us.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  net/key/af_key.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/key/af_key.c b/net/key/af_key.c
> index b67ed3a8486c..ced54144d5fd 100644
> --- a/net/key/af_key.c
> +++ b/net/key/af_key.c
> @@ -3087,6 +3087,8 @@ static int pfkey_send_policy_notify(struct xfrm_policy *xp, int dir, const struc
>  	case XFRM_MSG_DELPOLICY:
>  	case XFRM_MSG_NEWPOLICY:
>  	case XFRM_MSG_UPDPOLICY:
> +		if (!xp)
> +			break;

I think this can not happen. Who sends one of these notifications
without a pointer to the policy?