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[84.238.136.197]) by smtp.gmail.com with ESMTPSA id l9sm1957126lje.57.2020.05.06.13.31.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 May 2020 13:31:18 -0700 (PDT) Subject: Re: [Patch net v2] net: fix a potential recursive NETDEV_FEAT_CHANGE To: Cong Wang , netdev@vger.kernel.org Cc: syzbot+e73ceacfd8560cc8a3ca@syzkaller.appspotmail.com, syzbot+c2fb6f9ddcea95ba49b5@syzkaller.appspotmail.com, Josh Poimboeuf , Jay Vosburgh , Jann Horn References: <20200506194613.18342-1-xiyou.wangcong@gmail.com> From: Nikolay Aleksandrov Message-ID: Date: Wed, 6 May 2020 23:31:16 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200506194613.18342-1-xiyou.wangcong@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 06/05/2020 22:46, Cong Wang wrote: > syzbot managed to trigger a recursive NETDEV_FEAT_CHANGE event > between bonding master and slave. I managed to find a reproducer > for this: > > ip li set bond0 up > ifenslave bond0 eth0 > brctl addbr br0 > ethtool -K eth0 lro off > brctl addif br0 bond0 > ip li set br0 up > > When a NETDEV_FEAT_CHANGE event is triggered on a bonding slave, > it captures this and calls bond_compute_features() to fixup its > master's and other slaves' features. However, when syncing with > its lower devices by netdev_sync_lower_features() this event is > triggered again on slaves when the LRO feature fails to change, > so it goes back and forth recursively until the kernel stack is > exhausted. > > Commit 17b85d29e82c intentionally lets __netdev_update_features() > return -1 for such a failure case, so we have to just rely on > the existing check inside netdev_sync_lower_features() and skip > NETDEV_FEAT_CHANGE event only for this specific failure case. > > Fixes: 17b85d29e82c ("net/core: revert "net: fix __netdev_update_features return.." and add comment") > Reported-by: syzbot+e73ceacfd8560cc8a3ca@syzkaller.appspotmail.com > Reported-by: syzbot+c2fb6f9ddcea95ba49b5@syzkaller.appspotmail.com > Cc: Nikolay Aleksandrov > Cc: Josh Poimboeuf > Cc: Jay Vosburgh > Cc: Jann Horn > Signed-off-by: Cong Wang > --- The patch looks good, but note that __netdev_update_features() used to return -1 before the commit in the Fixes tag above (between 6cb6a27c45ce and 00ee59271777). It only restored that behaviour. > net/core/dev.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/net/core/dev.c b/net/core/dev.c > index 522288177bbd..6d327b7aa813 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -8907,11 +8907,13 @@ static void netdev_sync_lower_features(struct net_device *upper, > netdev_dbg(upper, "Disabling feature %pNF on lower dev %s.\n", > &feature, lower->name); > lower->wanted_features &= ~feature; > - netdev_update_features(lower); > + __netdev_update_features(lower); > > if (unlikely(lower->features & feature)) > netdev_WARN(upper, "failed to disable %pNF on %s!\n", > &feature, lower->name); > + else > + netdev_features_change(lower); > } > } > } >