CVE-2026-64537: bridge: cfm: reject invalid CCM interval at configuration time

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

bridge: cfm: reject invalid CCM interval at configuration time

ccm_tx_work_expired() re-arms itself via queue_delayed_work() using
the configured exp_interval converted by interval_to_us(). When
exp_interval is BR_CFM_CCM_INTERVAL_NONE or out of range,
interval_to_us() returns 0, causing the worker to fire immediately in
a tight loop that allocates skbs until OOM.

Fix this by validating exp_interval at configuration time:

 - Constrain IFLA_BRIDGE_CFM_CC_CONFIG_EXP_INTERVAL to the valid range
   [BR_CFM_CCM_INTERVAL_3_3_MS, BR_CFM_CCM_INTERVAL_10_MIN] in the
   netlink policy so userspace cannot set an invalid value.

 - Reject starting CCM TX in br_cfm_cc_ccm_tx() when exp_interval has
   not yet been configured (defaults to 0 from kzalloc).

The Linux kernel CVE team has assigned CVE-2026-64537 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.11 with commit 2be665c3940d367e0a2a8128eb4985ce323f99a3 and fixed in 5.15.212 with commit 2870056a78961e0fecd652362ee9d3fcfd24a8a6
	Issue introduced in 5.11 with commit 2be665c3940d367e0a2a8128eb4985ce323f99a3 and fixed in 6.1.178 with commit f0f5eb59a97ece0d85de8cfa95dc18c609302a8b
	Issue introduced in 5.11 with commit 2be665c3940d367e0a2a8128eb4985ce323f99a3 and fixed in 6.6.145 with commit 53788b134519e995699ea3721969c96a08d64575
	Issue introduced in 5.11 with commit 2be665c3940d367e0a2a8128eb4985ce323f99a3 and fixed in 6.12.97 with commit b42aeb58317f12024734759ff745856b53948873
	Issue introduced in 5.11 with commit 2be665c3940d367e0a2a8128eb4985ce323f99a3 and fixed in 6.18.40 with commit a090880c1f544589427e5b7050c40fb211ccecb4
	Issue introduced in 5.11 with commit 2be665c3940d367e0a2a8128eb4985ce323f99a3 and fixed in 7.1.5 with commit 865643640b5b5c4579b32d7a55ac9ad648362eaa
	Issue introduced in 5.11 with commit 2be665c3940d367e0a2a8128eb4985ce323f99a3 and fixed in 7.2-rc1 with commit f3e02edd8322b31b8e6517faa6ba053bf29d1e26

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64537
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/bridge/br_cfm.c
	net/bridge/br_cfm_netlink.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/2870056a78961e0fecd652362ee9d3fcfd24a8a6
	https://git.kernel.org/stable/c/f0f5eb59a97ece0d85de8cfa95dc18c609302a8b
	https://git.kernel.org/stable/c/53788b134519e995699ea3721969c96a08d64575
	https://git.kernel.org/stable/c/b42aeb58317f12024734759ff745856b53948873
	https://git.kernel.org/stable/c/a090880c1f544589427e5b7050c40fb211ccecb4
	https://git.kernel.org/stable/c/865643640b5b5c4579b32d7a55ac9ad648362eaa
	https://git.kernel.org/stable/c/f3e02edd8322b31b8e6517faa6ba053bf29d1e26