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From: Guillaume Nault <gnault@redhat.com>
To: Tom Parkin <tparkin@katalix.com>
Cc: lyl2019@mail.ustc.edu.cn, 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: Mon, 15 Mar 2021 12:04:07 +0000	[thread overview]
Message-ID: <20210315120407.GB4296@linux.home> (raw)
In-Reply-To: <20210312101258.GA4951@katalix.com>

On Fri, Mar 12, 2021 at 10:12:58AM +0000, Tom Parkin wrote:
> 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.

Agreed: ppp_unregister_channel() is going to drop a refcount from pch
in any case. So holding a refcount on pch is a hard requirement for any
caller of ppp_unregister_channel(), regardless of the channel bridging
code.

To lyl2019: Note that this refcount is (unsurprisingly) held by calling
ppp_register_net_channel().

  parent reply	other threads:[~2021-03-15 12:04 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
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 [this message]
2021-03-15 11:50 ` Guillaume Nault

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