Messages in this thread | | | Date | Fri, 12 Mar 2021 10:12:58 +0000 | From | Tom Parkin <> | Subject | Re: [BUG] net/ppp: A use after free in ppp_unregister_channe |
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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. [unhandled content-type:application/pgp-signature] | |