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Message-ID: <2025022708-CVE-2025-21823-9027@gregkh> Date: Thu, 27 Feb 2025 12:05:10 -0800 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: CVE-2025-21823: batman-adv: Drop unmanaged ELP metric worker 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) The Linux kernel CVE team has assigned CVE-2025-21823 to this issue. Affected and fixed versions =========================== Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.1.129 with commit 781a06fd265a8151f7601122d9c2e985663828ff Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.6.79 with commit a7aa2317285806640c844acd4cd2cd768e395264 Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.12.16 with commit 0fdc3c166ac17b26014313fa2b93696354511b24 Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.13.4 with commit af264c2a9adc37f4bdf88ca7f3affa15d8c7de9e Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.14-rc3 with commit 8c8ecc98f5c65947b0070a24bac11e12e47cc65d 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-2025-21823 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/batman-adv/bat_v.c net/batman-adv/bat_v_elp.c net/batman-adv/bat_v_elp.h net/batman-adv/types.h 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/781a06fd265a8151f7601122d9c2e985663828ff https://git.kernel.org/stable/c/a7aa2317285806640c844acd4cd2cd768e395264 https://git.kernel.org/stable/c/0fdc3c166ac17b26014313fa2b93696354511b24 https://git.kernel.org/stable/c/af264c2a9adc37f4bdf88ca7f3affa15d8c7de9e https://git.kernel.org/stable/c/8c8ecc98f5c65947b0070a24bac11e12e47cc65d
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