| 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-2023-52935: mm/khugepaged: fix ->anon_vma race |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| mm/khugepaged: fix ->anon_vma race |
| |
| If an ->anon_vma is attached to the VMA, collapse_and_free_pmd() requires |
| it to be locked. |
| |
| Page table traversal is allowed under any one of the mmap lock, the |
| anon_vma lock (if the VMA is associated with an anon_vma), and the |
| mapping lock (if the VMA is associated with a mapping); and so to be |
| able to remove page tables, we must hold all three of them. |
| retract_page_tables() bails out if an ->anon_vma is attached, but does |
| this check before holding the mmap lock (as the comment above the check |
| explains). |
| |
| If we racily merged an existing ->anon_vma (shared with a child |
| process) from a neighboring VMA, subsequent rmap traversals on pages |
| belonging to the child will be able to see the page tables that we are |
| concurrently removing while assuming that nothing else can access them. |
| |
| Repeat the ->anon_vma check once we hold the mmap lock to ensure that |
| there really is no concurrent page table access. |
| |
| Hitting this bug causes a lockdep warning in collapse_and_free_pmd(), |
| in the line "lockdep_assert_held_write(&vma->anon_vma->root->rwsem)". |
| It can also lead to use-after-free access. |
| |
| The Linux kernel CVE team has assigned CVE-2023-52935 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 4.8 with commit f3f0e1d2150b2b99da2cbdfaad000089efe9bf30 and fixed in 6.1.11 with commit acb08187b5a83cdb9ac4112fae9e18cf983b0128 |
| Issue introduced in 4.8 with commit f3f0e1d2150b2b99da2cbdfaad000089efe9bf30 and fixed in 6.2 with commit 023f47a8250c6bdb4aebe744db4bf7f73414028b |
| |
| 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-2023-52935 |
| 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: |
| mm/khugepaged.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/acb08187b5a83cdb9ac4112fae9e18cf983b0128 |
| https://git.kernel.org/stable/c/023f47a8250c6bdb4aebe744db4bf7f73414028b |
