CVE-2021-47371: In the Linux kernel, the following vulnerability has been resolved: nexthop: Fix memory leaks in nexthop notification chain listeners syzkaller discovered…

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

nexthop: Fix memory leaks in nexthop notification chain listeners

syzkaller discovered memory leaks [1] that can be reduced to the
following commands:

# ip nexthop add id 1 blackhole
# devlink dev reload pci/0000:06:00.0

As part of the reload flow, mlxsw will unregister its netdevs and then
unregister from the nexthop notification chain. Before unregistering
from the notification chain, mlxsw will receive delete notifications for
nexthop objects using netdevs registered by mlxsw or their uppers. mlxsw
will not receive notifications for nexthops using netdevs that are not
dismantled as part of the reload flow. For example, the blackhole
nexthop above that internally uses the loopback netdev as its nexthop
device.

One way to fix this problem is to have listeners flush their nexthop
tables after unregistering from the notification chain. This is
error-prone as evident by this patch and also not symmetric with the
registration path where a listener receives a dump of all the existing
nexthops.

Therefore, fix this problem by replaying delete notifications for the
listener being unregistered. This is symmetric to the registration path
and also consistent with the netdev notification chain.

The above means that unregister_nexthop_notifier(), like
register_nexthop_notifier(), will have to take RTNL in order to iterate
over the existing nexthops and that any callers of the function cannot
hold RTNL. This is true for mlxsw and netdevsim, but not for the VXLAN
driver. To avoid a deadlock, change the latter to unregister its nexthop
listener without holding RTNL, making it symmetric to the registration
path.

[1]
unreferenced object 0xffff88806173d600 (size 512):
comm "syz-executor.0", pid 1290, jiffies 4295583142 (age 143.507s)
hex dump (first 32 bytes):
41 9d 1e 60 80 88 ff ff 08 d6 73 61 80 88 ff ff A..`......sa....
08 d6 73 61 80 88 ff ff 01 00 00 00 00 00 00 00 ..sa............
backtrace:
[] kmemlea

Affected

CVSS provenance