netdev - Re: [PATCH] netlink: Safer deletion of sk_bind

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Message-Id: <20140901.220325.955861172520355423.davem@davemloft.net>
Date:	Mon, 01 Sep 2014 22:03:25 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	HarishJennyKN <harish_kandiga@...tor.com>
Cc:	dborkman@...hat.com, tgraf@...g.ch, ebiederm@...ssion.com,
	darkjames-ws@...kjames.pl, rgb@...hat.com, eric.dumazet@...il.com,
	stephen@...workplumber.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netlink: Safer deletion of sk_bind_node

From: Harish Jenny K N
Date: Mon, 1 Sep 2014 12:38:29 +0530

Firstly, you really need to fix your outgoing email so that your email
address appears in your From: header properly.

> From: Harish Jenny K N <harish_kandiga@...tor.com>
> 
>     Unable to handle kernel NULL pointer dereference at virtual address 00000000
>         (netlink_release+0x0/0x2a0) from [<8034e78c>] (sock_release+0x28/0xa4)
>         (sock_release+0x0/0xa4) from [<8034e830>] (sock_close+0x28/0x34)
>         (sock_close+0x0/0x34) from [<800f3490>] (__fput+0xf0/0x1ec)
>         (__fput+0x0/0x1ec) from [<800f3634>] (____fput+0x10/0x14)
>         (____fput+0x0/0x14) from [<80040a64>] (task_work_run+0xb8/0xd8)
>         (task_work_run+0x0/0xd8) from [<800113a0>] (do_work_pending+0xb0/0xc4)
>         (do_work_pending+0x0/0xc4) from [<8000d960>] (work_pending+0xc/0x20)
>     Call flow of the inline and static functions
>         netlink_release
>         -----netlink_remove
>         ---------__sk_del_bind_node
>         --------------__hlist_del
> 
> Signed-off-by: Harish Jenny K N <harish_kandiga@...tor.com>

This doesn't tell us anything about how this situation can be
arrived at.

When subscriptions changes, we delete the node with the table lock
held if subscriptions goes to zero.  We only try to delete the node
when subscriptions was zero.
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