| From bippy-7c5fe7eed585 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-2025-21896: fuse: revert back to __readahead_folio() for readahead |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| fuse: revert back to __readahead_folio() for readahead |
| |
| In commit 3eab9d7bc2f4 ("fuse: convert readahead to use folios"), the |
| logic was converted to using the new folio readahead code, which drops |
| the reference on the folio once it is locked, using an inferred |
| reference on the folio. Previously we held a reference on the folio for |
| the entire duration of the readpages call. |
| |
| This is fine, however for the case for splice pipe responses where we |
| will remove the old folio and splice in the new folio (see |
| fuse_try_move_page()), we assume that there is a reference held on the |
| folio for ap->folios, which is no longer the case. |
| |
| To fix this, revert back to __readahead_folio() which allows us to hold |
| the reference on the folio for the duration of readpages until either we |
| drop the reference ourselves in fuse_readpages_end() or the reference is |
| dropped after it's replaced in the page cache in the splice case. |
| This will fix the UAF bug that was reported. |
| |
| The Linux kernel CVE team has assigned CVE-2025-21896 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.13 with commit 3eab9d7bc2f4ae7f3f9c9c7852ff61600df79856 and fixed in 6.13.6 with commit 60db11f1b7fba4a66b117ea998d965818784a98d |
| Issue introduced in 6.13 with commit 3eab9d7bc2f4ae7f3f9c9c7852ff61600df79856 and fixed in 6.14 with commit 0c67c37e1710b2a8f61c8a02db95a51fe577e2c1 |
| |
| 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-2025-21896 |
| 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: |
| fs/fuse/dev.c |
| fs/fuse/file.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/60db11f1b7fba4a66b117ea998d965818784a98d |
| https://git.kernel.org/stable/c/0c67c37e1710b2a8f61c8a02db95a51fe577e2c1 |
