Stephen Hemminger
2017-Apr-07 17:37 UTC
[Bridge] [PATCH net] bridge: netlink: register netdevice before executing changelink
On Fri, 7 Apr 2017 18:43:06 +0300 Nikolay Aleksandrov <nikolay at cumulusnetworks.com> wrote:> On 07/04/17 18:36, Stephen Hemminger wrote: > > On Fri, 7 Apr 2017 18:27:37 +0300 > > Nikolay Aleksandrov <nikolay at cumulusnetworks.com> wrote: > > > >> On 07/04/17 18:22, Stephen Hemminger wrote: > >>> On Fri, 7 Apr 2017 17:19:48 +0300 > >>> Nikolay Aleksandrov <nikolay at cumulusnetworks.com> wrote: > >>> > >>>> On 07/04/17 17:10, Stephen Hemminger wrote: > >>>>> On Fri, 7 Apr 2017 15:49:15 +0300 > >>>>> <idosch at mellanox.com> wrote: > >>>>> > >>>>>> From: Ido Schimmel <idosch at mellanox.com> > >>>>>> > >>>>>> Peter reported a kernel oops when executing the following command: > >>>>>> > >>>>>> $ ip link add name test type bridge vlan_default_pvid 1 > >>>>>> > >>>>>> [13634.939408] BUG: unable to handle kernel NULL pointer dereference at > >>>>>> 0000000000000190 > >>>>>> [13634.939436] IP: __vlan_add+0x73/0x5f0 > >>>>>> [...] > >>>>>> [13634.939783] Call Trace: > >>>>>> [13634.939791] ? pcpu_next_unpop+0x3b/0x50 > >>>>>> [13634.939801] ? pcpu_alloc+0x3d2/0x680 > >>>>>> [13634.939810] ? br_vlan_add+0x135/0x1b0 > >>>>>> [13634.939820] ? __br_vlan_set_default_pvid.part.28+0x204/0x2b0 > >>>>>> [13634.939834] ? br_changelink+0x120/0x4e0 > >>>>>> [13634.939844] ? br_dev_newlink+0x50/0x70 > >>>>>> [13634.939854] ? rtnl_newlink+0x5f5/0x8a0 > >>>>>> [13634.939864] ? rtnl_newlink+0x176/0x8a0 > >>>>>> [13634.939874] ? mem_cgroup_commit_charge+0x7c/0x4e0 > >>>>>> [13634.939886] ? rtnetlink_rcv_msg+0xe1/0x220 > >>>>>> [13634.939896] ? lookup_fast+0x52/0x370 > >>>>>> [13634.939905] ? rtnl_newlink+0x8a0/0x8a0 > >>>>>> [13634.939915] ? netlink_rcv_skb+0xa1/0xc0 > >>>>>> [13634.939925] ? rtnetlink_rcv+0x24/0x30 > >>>>>> [13634.939934] ? netlink_unicast+0x177/0x220 > >>>>>> [13634.939944] ? netlink_sendmsg+0x2fe/0x3b0 > >>>>>> [13634.939954] ? _copy_from_user+0x39/0x40 > >>>>>> [13634.939964] ? sock_sendmsg+0x30/0x40 > >>>>>> [13634.940159] ? ___sys_sendmsg+0x29d/0x2b0 > >>>>>> [13634.940326] ? __alloc_pages_nodemask+0xdf/0x230 > >>>>>> [13634.940478] ? mem_cgroup_commit_charge+0x7c/0x4e0 > >>>>>> [13634.940592] ? mem_cgroup_try_charge+0x76/0x1a0 > >>>>>> [13634.940701] ? __handle_mm_fault+0xdb9/0x10b0 > >>>>>> [13634.940809] ? __sys_sendmsg+0x51/0x90 > >>>>>> [13634.940917] ? entry_SYSCALL_64_fastpath+0x1e/0xad > >>>>>> > >>>>>> The problem is that the bridge's VLAN group is created after setting the > >>>>>> default PVID, when registering the netdevice and executing its > >>>>>> ndo_init(). > >>>>>> > >>>>>> Fix this by changing the order of both operations, so that > >>>>>> br_changelink() is only processed after the netdevice is registered, > >>>>>> when the VLAN group is already initialized. > >>>>>> > >>>>>> The changelink() call is done on a best-effort basis since unregistering > >>>>>> the netdevice upon failure won't perform a proper cleanup due to a > >>>>>> missing ndo_uninit(), which I'll try to add for net-next. > >>>>>> > >>>>>> Fixes: b6677449dff6 ("bridge: netlink: call br_changelink() during br_dev_newlink()") > >>>>>> Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com> > >>>>>> Signed-off-by: Ido Schimmel <idosch at mellanox.com> > >>>>>> Reported-by: Peter V. Saveliev <peter at svinota.eu> > >>>>>> --- > >>>>>> Please consider this for 4.4.y, 4.9.y and 4.10.y as well. > >>>>> > >>>>> Although this patch fixes the OOPS it breaks all the error handling > >>>>> of br_changelink. If bad attributes are passed to newlink, you leave a > >>>>> broken partially configured bridge device. The code needs to cleanup > >>>>> and return the correct errno. > >>>>> > >>>> > >>>> The cleanup would require adding ndo_uninit() and a much bigger churn > >>>> which doesn't seem okay for -net, it will be targetted at net-next. > >>>> The bridge can always be reconfigured as all of the options can be set > >>>> during runtime, so anything can be fixed, thus the best-effort changelink. > >>>> > >>>> If it is not desirable for -net then maybe we should just revert the > >>>> patch there altogether and make it again correctly with cleanup and so > >>>> on in net-next. > >>>> > >>>> > >>>> > >>> > >>> Why not just add pointer validation in the PVID attribute parsing. > >>> > >> > >> We cannot have the changelink() before the register for many reasons, > >> first the vlan config will not be applied so all of the vlan options > >> won't get set even though they're passed, then the changelink() can > >> cause more trouble via the STP calls (f.e. br_stp_start) which can use > >> br->dev->ifindex (= 0 at that point), also can use br->dev->name (still > >> haven't passed validation and is uninitialized, i.e. > >> dev_get_valid_name() hasn't been called and we can have format > >> specifiers in it), multicast code also has some codepaths that will > >> cause various timers to get started... > >> > >> Moving changelink() after the register is much safer. > >> > > > > Then just fix error handling. Why not call unregister? > > > > Right, because there's no ndo_uninit() and this will not cleanup the > bridge properly. That's the plan for net-next, reorg the code and add > ndo_uninit() for that reason. > > From Ido's commit message above: > "The changelink() call is done on a best-effort basis since > unregistering the netdevice upon failure won't perform a proper cleanup > due to a missing ndo_uninit(), which I'll try to add for net-next."Fix it right now. The patch you propose is too half baked.
Ido Schimmel
2017-Apr-07 18:16 UTC
[Bridge] [PATCH net] bridge: netlink: register netdevice before executing changelink
On Fri, Apr 07, 2017 at 01:37:53PM -0400, Stephen Hemminger wrote:> Fix it right now. The patch you propose is too half baked.Given this patch needs to be back ported to three different stable kernels I tried to keep the amount of changes to a minimum while fixing the bug. I'll work on the ndo_uninit() patch and submit it. Then people can decide which course of action they're more comfortable with.