Jiri Pirko [off-list ref] wrote:

Mon, Sep 16, 2019 at 03:47:54PM CEST, ap420073@gmail.com wrote:

quoted

The IFF_BONDING means bonding master or bonding slave device.
->ndo_add_slave() sets IFF_BONDING flag and ->ndo_del_slave() unsets
IFF_BONDING flag.

bond0<--bond1

Both bond0 and bond1 are bonding device and these should keep having
IFF_BONDING flag until they are removed.
But bond1 would lose IFF_BONDING at ->ndo_del_slave() because that routine
do not check whether the slave device is the bonding type or not.
This patch adds the interface type check routine before removing
IFF_BONDING flag.

Test commands:
   ip link add bond0 type bond
   ip link add bond1 type bond
   ip link set bond1 master bond0
   ip link set bond1 nomaster
   ip link del bond1 type bond
   ip link add bond1 type bond

Interesting. I wonder why bond-in-bond is not forbidden...

	I think mostly because nesting wasn't originally forbidden, and
there are apparently users of it out in the wild, judging from the
number of times I see configurations or queries about an active-backup
bond with two 802.3ad bonding slaves.  That particular configuration
doesn't have any advantage (802.3ad will internally manage that
situation), but I don't see that we can now forbid nesting bonds without
potentially breaking existing user space configurations.

	-J

---
	-Jay Vosburgh, jay.vosburgh@canonical.com