| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2025-21767: clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context |
| |
| The following bug report happened with a PREEMPT_RT kernel: |
| |
| BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48 |
| in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2012, name: kwatchdog |
| preempt_count: 1, expected: 0 |
| RCU nest depth: 0, expected: 0 |
| get_random_u32+0x4f/0x110 |
| clocksource_verify_choose_cpus+0xab/0x1a0 |
| clocksource_verify_percpu.part.0+0x6b/0x330 |
| clocksource_watchdog_kthread+0x193/0x1a0 |
| |
| It is due to the fact that clocksource_verify_choose_cpus() is invoked with |
| preemption disabled. This function invokes get_random_u32() to obtain |
| random numbers for choosing CPUs. The batched_entropy_32 local lock and/or |
| the base_crng.lock spinlock in driver/char/random.c will be acquired during |
| the call. In PREEMPT_RT kernel, they are both sleeping locks and so cannot |
| be acquired in atomic context. |
| |
| Fix this problem by using migrate_disable() to allow smp_processor_id() to |
| be reliably used without introducing atomic context. preempt_disable() is |
| then called after clocksource_verify_choose_cpus() but before the |
| clocksource measurement is being run to avoid introducing unexpected |
| latency. |
| |
| The Linux kernel CVE team has assigned CVE-2025-21767 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.10.50 with commit d9b40ebd448e437ffbc65f013836f98252279a82 and fixed in 5.10.235 with commit d9c217fadfcff7a8df58567517d1e4253f3fd243 |
| Issue introduced in 5.14 with commit 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and fixed in 5.15.179 with commit 60f54f0d4ea530950549a8263e6fdd70a40490a4 |
| Issue introduced in 5.14 with commit 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and fixed in 6.1.129 with commit 852805b6cbdb69c298a8fc9fbe79994c95106e04 |
| Issue introduced in 5.14 with commit 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and fixed in 6.6.79 with commit 8783ceeee797d9aa9cfe150690fb9d0bac8cc459 |
| Issue introduced in 5.14 with commit 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and fixed in 6.12.16 with commit cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa |
| Issue introduced in 5.14 with commit 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and fixed in 6.13.4 with commit 0fb534187d2355f6c8f995321e76d1ccd1262ac1 |
| Issue introduced in 5.14 with commit 7560c02bdffb7c52d1457fa551b9e745d4b9e754 and fixed in 6.14 with commit 6bb05a33337b2c842373857b63de5c9bf1ae2a09 |
| Issue introduced in 5.12.17 with commit 193e14e68e907b2a7a936a7726accbaa4df25a4d |
| Issue introduced in 5.13.2 with commit 155d3c5d24ee13cafa6236b49fc02b240a511d59 |
| |
| 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-2025-21767 |
| 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: |
| kernel/time/clocksource.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/d9c217fadfcff7a8df58567517d1e4253f3fd243 |
| https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4 |
| https://git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04 |
| https://git.kernel.org/stable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459 |
| https://git.kernel.org/stable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa |
| https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1 |
| https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09 |
