| 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-2025-21664: dm thin: make get_first_thin use rcu-safe list first function |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| dm thin: make get_first_thin use rcu-safe list first function |
| |
| The documentation in rculist.h explains the absence of list_empty_rcu() |
| and cautions programmers against relying on a list_empty() -> |
| list_first() sequence in RCU safe code. This is because each of these |
| functions performs its own READ_ONCE() of the list head. This can lead |
| to a situation where the list_empty() sees a valid list entry, but the |
| subsequent list_first() sees a different view of list head state after a |
| modification. |
| |
| In the case of dm-thin, this author had a production box crash from a GP |
| fault in the process_deferred_bios path. This function saw a valid list |
| head in get_first_thin() but when it subsequently dereferenced that and |
| turned it into a thin_c, it got the inside of the struct pool, since the |
| list was now empty and referring to itself. The kernel on which this |
| occurred printed both a warning about a refcount_t being saturated, and |
| a UBSAN error for an out-of-bounds cpuid access in the queued spinlock, |
| prior to the fault itself. When the resulting kdump was examined, it |
| was possible to see another thread patiently waiting in thin_dtr's |
| synchronize_rcu. |
| |
| The thin_dtr call managed to pull the thin_c out of the active thins |
| list (and have it be the last entry in the active_thins list) at just |
| the wrong moment which lead to this crash. |
| |
| Fortunately, the fix here is straight forward. Switch get_first_thin() |
| function to use list_first_or_null_rcu() which performs just a single |
| READ_ONCE() and returns NULL if the list is already empty. |
| |
| This was run against the devicemapper test suite's thin-provisioning |
| suites for delete and suspend and no regressions were observed. |
| |
| The Linux kernel CVE team has assigned CVE-2025-21664 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 3.15 with commit b10ebd34cccae1b431caf1be54919aede2be7cbe and fixed in 5.4.290 with commit ec037fe8c0d0f6140e3d8a49c7b29cb5582160b8 |
| Issue introduced in 3.15 with commit b10ebd34cccae1b431caf1be54919aede2be7cbe and fixed in 5.10.234 with commit cd30a3960433ec2db94b3689752fa3c5df44d649 |
| Issue introduced in 3.15 with commit b10ebd34cccae1b431caf1be54919aede2be7cbe and fixed in 5.15.177 with commit 802666a40c71a23542c43a3f87e3a2d0f4e8fe45 |
| Issue introduced in 3.15 with commit b10ebd34cccae1b431caf1be54919aede2be7cbe and fixed in 6.1.125 with commit 12771050b6d059eea096993bf2001da9da9fddff |
| Issue introduced in 3.15 with commit b10ebd34cccae1b431caf1be54919aede2be7cbe and fixed in 6.6.72 with commit 6b305e98de0d225ccebfb225730a9f560d28ecb0 |
| Issue introduced in 3.15 with commit b10ebd34cccae1b431caf1be54919aede2be7cbe and fixed in 6.12.10 with commit cbd0d5ecfa390ac29c5380200147d09c381b2ac6 |
| Issue introduced in 3.15 with commit b10ebd34cccae1b431caf1be54919aede2be7cbe and fixed in 6.13 with commit 80f130bfad1dab93b95683fc39b87235682b8f72 |
| |
| 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-2025-21664 |
| 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: |
| drivers/md/dm-thin.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/ec037fe8c0d0f6140e3d8a49c7b29cb5582160b8 |
| https://git.kernel.org/stable/c/cd30a3960433ec2db94b3689752fa3c5df44d649 |
| https://git.kernel.org/stable/c/802666a40c71a23542c43a3f87e3a2d0f4e8fe45 |
| https://git.kernel.org/stable/c/12771050b6d059eea096993bf2001da9da9fddff |
| https://git.kernel.org/stable/c/6b305e98de0d225ccebfb225730a9f560d28ecb0 |
| https://git.kernel.org/stable/c/cbd0d5ecfa390ac29c5380200147d09c381b2ac6 |
| https://git.kernel.org/stable/c/80f130bfad1dab93b95683fc39b87235682b8f72 |
