[Bridge] [PATCH net] bridge: netlink: register netdevice before executing changelink

Stephen Hemminger stephen at networkplumber.org
Fri Apr 7 15:22:06 UTC 2017


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.


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