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[2a01:cb05:8918:ce00:dd1a:5a4f:9908:f2d5]) by smtp.gmail.com with ESMTPSA id m8sm15033298wmc.27.2020.12.07.08.22.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Dec 2020 08:22:30 -0800 (PST) Date: Mon, 7 Dec 2020 17:22:28 +0100 From: Guillaume Nault To: Tom Parkin Cc: netdev@vger.kernel.org, jchapman@katalix.com Subject: Re: [PATCH v3 net-next 1/2] ppp: add PPPIOCBRIDGECHAN and PPPIOCUNBRIDGECHAN ioctls Message-ID: <20201207162228.GA28888@linux.home> References: <20201204163656.1623-1-tparkin@katalix.com> <20201204163656.1623-2-tparkin@katalix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201204163656.1623-2-tparkin@katalix.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Dec 04, 2020 at 04:36:55PM +0000, Tom Parkin wrote: > +static int ppp_unbridge_channels(struct channel *pch) > +{ > + struct channel *pchb, *pchbb; > + > + write_lock_bh(&pch->upl); > + pchb = rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl)); > + if (!pchb) { > + write_unlock_bh(&pch->upl); > + return -EINVAL; > + } > + RCU_INIT_POINTER(pch->bridge, NULL); > + write_unlock_bh(&pch->upl); > + > + write_lock_bh(&pchb->upl); > + pchbb = rcu_dereference_protected(pchb->bridge, lockdep_is_held(&pchb->upl)); > + if (pchbb == pch) > + RCU_INIT_POINTER(pchb->bridge, NULL); > + write_unlock_bh(&pchb->upl); > + > + synchronize_rcu(); > + > + if (pchbb == pch) > + if (refcount_dec_and_test(&pch->file.refcnt)) > + ppp_destroy_channel(pch); Since a respin is needed (see below), maybe add a comment explaining why we need to verify that pchbb == pch. > + if (refcount_dec_and_test(&pchb->file.refcnt)) > + ppp_destroy_channel(pchb); > + > + return 0; > +} > + > static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) > { > struct ppp_file *pf; > @@ -641,8 +714,9 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) > } > > if (pf->kind == CHANNEL) { > - struct channel *pch; > + struct channel *pch, *pchb; > struct ppp_channel *chan; > + struct ppp_net *pn; > > pch = PF_TO_CHANNEL(pf); > > @@ -657,6 +731,29 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) > err = ppp_disconnect_channel(pch); > break; > > + 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. > + 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.