On Mon, Dec 07, 2020 at 17:22:28 +0100, Guillaume Nault wrote: > On Fri, Dec 04, 2020 at 04:36:55PM +0000, Tom Parkin wrote: > > + case PPPIOCBRIDGECHAN: > > + if (get_user(unit, p)) > > + break; > > + err = -ENXIO; > > + pn = ppp_pernet(current->nsproxy->net_ns); > > + spin_lock_bh(&pn->all_channels_lock); > > + pchb = ppp_find_channel(pn, unit); > > + /* Hold a reference to prevent pchb being freed while > > + * we establish the bridge. > > + */ > > + if (pchb) > > + refcount_inc(&pchb->file.refcnt); > > The !pchb case isn't handled. With this code, if ppp_find_channel() > returns NULL, ppp_bridge_channels() will crash when trying to lock > pchb->upl.
Bleh :-( Apologies for this. I have stepped up my tests for "unhappy" code paths, and I'll try to run syzkaller at a v4 prior to re-submitting. > > + spin_unlock_bh(&pn->all_channels_lock); > > + err = ppp_bridge_channels(pch, pchb); > > + /* Drop earlier refcount now bridge establishment is > > complete */ > > + if (refcount_dec_and_test(&pchb->file.refcnt)) > > + ppp_destroy_channel(pchb); > > + break; > > + > > The rest looks good to me. Thanks!
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