netdev - Re: [PATCH ipsec] xfrm: policy: avoid warning splat when merging nodes

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Message-ID: <20190821064130.GN2879@gauss3.secunet.de>
Date:   Wed, 21 Aug 2019 08:41:30 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Florian Westphal <fw@...len.de>
CC:     <netdev@...r.kernel.org>, <syzkaller-bugs@...glegroups.com>,
        <syzbot+8cc27ace5f6972910b31@...kaller.appspotmail.com>
Subject: Re: [PATCH ipsec] xfrm: policy: avoid warning splat when merging
 nodes

On Mon, Aug 12, 2019 at 10:32:13AM +0200, Florian Westphal wrote:
> syzbot reported a splat:
>  xfrm_policy_inexact_list_reinsert+0x625/0x6e0 net/xfrm/xfrm_policy.c:877
>  CPU: 1 PID: 6756 Comm: syz-executor.1 Not tainted 5.3.0-rc2+ #57
>  Call Trace:
>   xfrm_policy_inexact_node_reinsert net/xfrm/xfrm_policy.c:922 [inline]
>   xfrm_policy_inexact_node_merge net/xfrm/xfrm_policy.c:958 [inline]
>   xfrm_policy_inexact_insert_node+0x537/0xb50 net/xfrm/xfrm_policy.c:1023
>   xfrm_policy_inexact_alloc_chain+0x62b/0xbd0 net/xfrm/xfrm_policy.c:1139
>   xfrm_policy_inexact_insert+0xe8/0x1540 net/xfrm/xfrm_policy.c:1182
>   xfrm_policy_insert+0xdf/0xce0 net/xfrm/xfrm_policy.c:1574
>   xfrm_add_policy+0x4cf/0x9b0 net/xfrm/xfrm_user.c:1670
>   xfrm_user_rcv_msg+0x46b/0x720 net/xfrm/xfrm_user.c:2676
>   netlink_rcv_skb+0x1f0/0x460 net/netlink/af_netlink.c:2477
>   xfrm_netlink_rcv+0x74/0x90 net/xfrm/xfrm_user.c:2684
>   netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
>   netlink_unicast+0x809/0x9a0 net/netlink/af_netlink.c:1328
>   netlink_sendmsg+0xa70/0xd30 net/netlink/af_netlink.c:1917
>   sock_sendmsg_nosec net/socket.c:637 [inline]
>   sock_sendmsg net/socket.c:657 [inline]
> 
> There is no reproducer, however, the warning can be reproduced
> by adding rules with ever smaller prefixes.
> 
> The sanity check ("does the policy match the node") uses the prefix value
> of the node before its updated to the smaller value.
> 
> To fix this, update the prefix earlier.  The bug has no impact on tree
> correctness, this is only to prevent a false warning.
> 
> Reported-by: syzbot+8cc27ace5f6972910b31@...kaller.appspotmail.com
> Signed-off-by: Florian Westphal <fw@...len.de>

Applied, thanks Florian!