linux-kernel - Re: [BUG] net: xfrm: possible null-pointer dereferences in xfrm

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Message-ID: <20190729080341.GJ2879@gauss3.secunet.de>
Date:   Mon, 29 Jul 2019 10:03:41 +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: [BUG] net: xfrm: possible null-pointer dereferences in
 xfrm_policy()

On Mon, Jul 29, 2019 at 11:43:49AM +0800, Jia-Ju Bai wrote:
> In xfrm_policy(), the while loop on lines 3802-3830 ends when dst->xfrm is
> NULL.

We don't have a xfrm_policy() function, and as said already the
line numbers does not help much as long as you don't say which
tree/branch this is and which commit is the head commit.

> Then, dst->xfrm is used on line 3840:
>     xfrm_state_mtu(dst->xfrm, mtu);
>         if (x->km.state != XFRM_STATE_VALID...)
>         aead = x->data;
> 
> Thus, possible null-pointer dereferences may occur.

I guess you refer to xfrm_bundle_ok(). The dst pointer
is reoaded after the loop, so the dereferenced pointer
is not the one that had NULL at dst->xfrm.

> 
> These bugs are found by a static analysis tool STCheck written by us.
> 
> I do not know how to correctly fix these bugs, so I only report them.

I'd suggest you to manually review the reports of your
tool and to fix the tool accordingly.