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Date:   Mon, 29 Jul 2019 10:03:41 +0200
From:   Steffen Klassert <steffen.klassert@secunet.com>
To:     Jia-Ju Bai <baijiaju1990@gmail.com>
CC:     <herbert@gondor.apana.org.au>, <davem@davemloft.net>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] net: xfrm: possible null-pointer dereferences in
 xfrm_policy()
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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.