Thanks for the report! On Thu, Mar 11, 2021 at 20:34:44 +0800, lyl2019@xxxxxxxxxxxxxxxx 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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