net: bridge: mdb: restart port group walk after deletion

Overview

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

net: bridge: mdb: restart port group walk after deletion

br_mdb_flush_pgs() keeps a pointer-to-pointer cursor while walking mp->ports. br_multicast_del_pg() can re-enter the same MDB entry through br_multicast_sg_del_exclude_ports() and unlink other port groups. If the cursor points into one of those groups, the next iteration dereferences a stale cursor and can leave mp->ports pointing at freed memory.

A following RTM_GETMDB exposes the dangling pointer:

BUG: KASAN: slab-use-after-free in br_mdb_dump Read of size 8 br_mdb_dump rtnl_mdb_dump rtnl_dumpit netlink_dump

Reset the cursor to mp->ports after every deletion. The deletion removes at least the selected group, so the restarted walk always makes progress.

Affected

• Linux >= a6acb535afb2a3b688a7858f05b61f0433e480d5 < 46ec55855c972504258c371677ac039ba20e5d12
• Linux >= a6acb535afb2a3b688a7858f05b61f0433e480d5 < ab3c4a4c85f2e1e8d04b5c1770dea8412d21c7fe
• Linux >= a6acb535afb2a3b688a7858f05b61f0433e480d5 < fe2a42789c12eb7c5d3a42191e2cc735a6c35ead
• Linux >= a6acb535afb2a3b688a7858f05b61f0433e480d5 < ab1404ac81154a89fb61ac50ae9a04cd8d4834dc
• Linux 6.8

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.