Description

In the Linux kernel, the following vulnerability has been resolved: batman-adv: Drop unmanaged ELP metric worker The ELP worker needs to calculate new metric values for all neighbors "reachable" over an interface. Some of the used metric sources require locks which might need to sleep. This sleep is incompatible with the RCU list iterator used for the recorded neighbors. The initial approach to work around of this problem was to queue another work item per neighbor and then run this in a new context. Even when this solved the RCU vs might_sleep() conflict, it has a major problems: Nothing was stopping the work item in case it is not needed anymore - for example because one of the related interfaces was removed or the batman-adv module was unloaded - resulting in potential invalid memory accesses. Directly canceling the metric worker also has various problems: * cancel_work_sync for a to-be-deactivated interface is called with rtnl_lock held. But the code in the ELP metric worker also tries to use rtnl_lock() - which will never return in this case. This also means that cancel_work_sync would never return because it is waiting for the worker to finish. * iterating over the neighbor list for the to-be-deactivated interface is currently done using the RCU specific methods. Which means that it is possible to miss items when iterating over it without the associated spinlock - a behaviour which is acceptable for a periodic metric check but not for a cleanup routine (which must "stop" all still running workers) The better approch is to get rid of the per interface neighbor metric worker and handle everything in the interface worker. The original problems are solved by: * creating a list of neighbors which require new metric information inside the RCU protected context, gathering the metric according to the new list outside the RCU protected context * only use rcu_trylock inside metric gathering code to avoid a deadlock when the cancel_delayed_work_sync is called in the interface removal code (which is called with the rtnl_lock held)

Affected Products 9

References 10

• git.kernel.org https://git.kernel.org/stable/c/0fdc3c166ac17b26014313fa2b93696354511b24
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• git.kernel.org https://git.kernel.org/stable/c/1c334629176c2d644befc31a20d4bf75542f7631
  Patch
• git.kernel.org https://git.kernel.org/stable/c/3c0e0aecb78cb2a2ca1dc701982d08fedb088dc6
  Patch
• git.kernel.org https://git.kernel.org/stable/c/781a06fd265a8151f7601122d9c2e985663828ff
  Patch
• git.kernel.org https://git.kernel.org/stable/c/8c8ecc98f5c65947b0070a24bac11e12e47cc65d
  Patch
• git.kernel.org https://git.kernel.org/stable/c/a0019971f340ae02ba54cf1861f72da7e03e6b66
  Patch
• git.kernel.org https://git.kernel.org/stable/c/a7aa2317285806640c844acd4cd2cd768e395264
  Patch
• git.kernel.org https://git.kernel.org/stable/c/af264c2a9adc37f4bdf88ca7f3affa15d8c7de9e
  Patch
• lists.debian.org https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
• lists.debian.org https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html

Remediation

• git.kernel.org https://git.kernel.org/stable/c/0fdc3c166ac17b26014313fa2b93696354511b24
  Patch
• git.kernel.org https://git.kernel.org/stable/c/1c334629176c2d644befc31a20d4bf75542f7631
  Patch
• git.kernel.org https://git.kernel.org/stable/c/3c0e0aecb78cb2a2ca1dc701982d08fedb088dc6
  Patch
• git.kernel.org https://git.kernel.org/stable/c/781a06fd265a8151f7601122d9c2e985663828ff
  Patch
• git.kernel.org https://git.kernel.org/stable/c/8c8ecc98f5c65947b0070a24bac11e12e47cc65d
  Patch
• git.kernel.org https://git.kernel.org/stable/c/a0019971f340ae02ba54cf1861f72da7e03e6b66
  Patch
• git.kernel.org https://git.kernel.org/stable/c/a7aa2317285806640c844acd4cd2cd768e395264
  Patch
• git.kernel.org https://git.kernel.org/stable/c/af264c2a9adc37f4bdf88ca7f3affa15d8c7de9e
  Patch