CVE-2026-46086

/// Technical description

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

net: bridge: use a stable FDB dst snapshot in RCU readers

Local FDB entries can be rewritten in place by `fdb_delete_local()`, which

updates `f->dst` to another port or to `NULL` while keeping the entry

alive. Several bridge RCU readers inspect `f->dst`, including

`br_fdb_fillbuf()` through the `brforward_read()` sysfs path.

These readers currently load `f->dst` multiple times and can therefore

observe inconsistent values across the check and later dereference.

In `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change

`f->dst` after the NULL check and before the `port_no` dereference,

leading to a NULL-ptr-deref.

Fix this by taking a single `READ_ONCE()` snapshot of `f->dst` in each

affected RCU reader and using that snapshot for the rest of the access

sequence. Also publish the in-place `f->dst` updates in `fdb_delete_local()`

with `WRITE_ONCE()` so the readers and writer use matching access patte

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References