CVE-2026-80838vxlan: keep the last remote linked during FDB flush

Official description

In the Linux kernel, the following vulnerability has been resolved: vxlan: keep the last remote linked during FDB flush A non-nexthop FDB entry is expected to have at least one remote while it remains reachable through the FDB hash table. A filtered bulk flush violates this invariant when every remote matches: It unlinks the last remote in vxlan_fdb_dst_destroy() and only afterwards tells vxlan_flush() to destroy the parent FDB entry. An RCU reader can find the parent during this interval. first_remote_rcu() then applies list_entry_rcu() to the empty list head, producing an invalid remote pointer that the receive learning path can read from and write to. When a matching remote is the sole remaining remote, leave it linked and ask the caller to destroy the entire FDB entry. vxlan_fdb_destroy() keeps the remote attached while sending the deletion notification and removing the parent from the lookup structures.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2a7c2f00843225d5f037676bca649321f3d024c7
• https://git.kernel.org/stable/c/a8820c8a7718327e96849782033e7c85a0f6bcfe
• https://git.kernel.org/stable/c/8ba68fd6cdd1e3c92b92f25c7e48bf7bd51a183c
• https://git.kernel.org/stable/c/4bbc76ee1b21d3bd045d6d819b2bacd30a6372ab
• https://git.kernel.org/stable/c/d5d4a7b538b52db63927773a8905fcd9f78a42e2