CVE-2023-53843

Summary

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

net: openvswitch: reject negative ifindex

Recent changes in net-next (commit 759ab1edb56c ("net: store netdevs in an xarray")) refactored the handling of pre-assigned ifindexes and let syzbot surface a latent problem in ovs. ovs does not validate ifindex, making it possible to create netdev ports with negative ifindex values. It's easy to repro with YNL:

$ ./cli.py –spec netlink/specs/ovs_datapath.yaml
–do new
–json '{"upcall-pid": 1, "name":"my-dp"}' $ ./cli.py –spec netlink/specs/ovs_vport.yaml
–do new
–json '{"upcall-pid": "00000001", "name": "some-port0", "dp-ifindex":3,"ifindex":4294901760,"type":2}'

$ ip link show -65536: some-port0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000 link/ether 7a:48:21:ad:0b:fb brd ff:ff:ff:ff:ff:ff …

Validate the inputs. Now the second command correctly returns:

$ ./cli.py –spec netlink/specs/ovs_vport.yaml
–do new
–json '{"upcall-pid": "00000001", "name": "some-port0", "dp-ifindex":3,"ifindex":4294901760,"type":2}'

lib.ynl.NlError: Netlink error: Numerical result out of range nl_len = 108 (92) nl_flags = 0x300 nl_type = 2 error: -34 extack: {'msg': 'integer out of range', 'unknown': [[type:4 len:36] b'\x0c\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0c\x00\x03\x00\xff\xff\xff\x7f\x00\x00\x00\x00\x08\x00\x01\x00\x08\x00\x00\x00'], 'bad-attr': '.ifindex'}

Accept 0 since it used to be silently ignored.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/c965a58376146dcfdda186819462e8eb3aadef3a
• https://git.kernel.org/stable/c/881faff9e548a7ddfb11595be7c1c649217d27db
• https://git.kernel.org/stable/c/a552bfa16bab4ce901ee721346a28c4e483f4066

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