Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

bonding: restore bond's IFF_SLAVE flag if a non-eth dev enslave fails

syzbot reported a warning[1] where the bond device itself is a slave and we try to enslave a non-ethernet device as the first slave which fails but then in the error path when ether_setup() restores the bond device it also clears all flags. In my previous fix[2] I restored the IFF_MASTER flag, but I didn't consider the case that the bond device itself might also be a slave with IFF_SLAVE set, so we need to restore that flag as well. Use the bond_ether_setup helper which does the right thing and restores the bond's flags properly.

Steps to reproduce using a nlmon dev: $ ip l add nlmon0 type nlmon $ ip l add bond1 type bond $ ip l add bond2 type bond $ ip l set bond1 master bond2 $ ip l set dev nlmon0 master bond1 $ ip -d l sh dev bond1 22: bond1: <BROADCAST,MULTICAST,MASTER> mtu 1500 qdisc noqueue master bond2 state DOWN mode DEFAULT group default qlen 1000 (now bond1's IFF_SLAVE flag is gone and we'll hit a warning[3] if we try to delete it)

[1] https://syzkaller.appspot.com/bug?id=391c7b1f6522182899efba27d891f1743e8eb3ef [2] commit 7d5cd2ce5292 ("bonding: correctly handle bonding type change on enslave failure") [3] example warning: [ 27.008664] bond1: (slave nlmon0): The slave device specified does not support setting the MAC address [ 27.008692] bond1: (slave nlmon0): Error -95 calling set_mac_address [ 32.464639]…