From: Tom Parkin <email@example.com> To: firstname.lastname@example.org Cc: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com 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.firstname.lastname@example.org> [-- Attachment #1: Type: text/plain, Size: 1239 bytes --] Thanks for the report! On Thu, Mar 11, 2021 at 20:34:44 +0800, email@example.com 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. [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 488 bytes --]
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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