From: Tom Parkin <tparkin@katalix.com>
To: lyl2019@mail.ustc.edu.cn
Cc: paulus@samba.org, davem@davemloft.net, linux-ppp@vger.kernel.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [BUG] net/ppp: A use after free in ppp_unregister_channe
Date: Fri, 12 Mar 2021 10:12:58 +0000 [thread overview]
Message-ID: <20210312101258.GA4951@katalix.com> (raw)
In-Reply-To: <6057386d.ca12.1782148389e.Coremail.lyl2019@mail.ustc.edu.cn>
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Thanks for the report!
On Thu, Mar 11, 2021 at 20:34:44 +0800, lyl2019@mail.ustc.edu.cn wrote:
> File: drivers/net/ppp/ppp_generic.c
>
> In ppp_unregister_channel, pch could be freed in ppp_unbridge_channels()
> but after that pch is still in use. Inside the function ppp_unbridge_channels,
> if "pchbb == pch" is true and then pch will be freed.
Do you have a way to reproduce a use-after-free scenario?
From static analysis I'm not sure how pch would be freed in
ppp_unbridge_channels when called via. ppp_unregister_channel.
In theory (at least!) the caller of ppp_register_net_channel holds
a reference on struct channel which ppp_unregister_channel drops.
Each channel in a bridged pair holds a reference on the other.
Hence on return from ppp_unbridge_channels, the channel should not have
been freed (in this code path) because the ppp_register_net_channel
reference has not yet been dropped.
Maybe there is an issue with the reference counting or a race of some
sort?
> I checked the commit history and found that this problem is introduced from
> 4cf476ced45d7 ("ppp: add PPPIOCBRIDGECHAN and PPPIOCUNBRIDGECHAN ioctls").
>
> I have no idea about how to generate a suitable patch, sorry.
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next prev parent reply other threads:[~2021-03-12 10:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-11 12:34 lyl2019
2021-03-12 10:12 ` Tom Parkin [this message]
2021-03-12 14:47 ` lyl2019
2021-03-15 9:57 ` Tom Parkin
2021-03-15 12:18 ` Guillaume Nault
2021-03-15 16:58 ` Tom Parkin
2021-03-15 12:04 ` Guillaume Nault
2021-03-15 11:50 ` Guillaume Nault
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