From: Jann Horn jannh@google.com

stable inclusion from stable-v6.6.51 commit 4a594acc12d5954cdc71d4450a386748bf3d136a category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAU9P2 CVE: CVE-2024-46838

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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commit 4828d207dc5161dc7ddf9a4f6dcfd80c7dd7d20a upstream.

Since khugepaged was changed to allow retracting page tables in file mappings without holding the mmap lock, these BUG_ON()s are wrong - get rid of them.

We could also remove the preceding "if (unlikely(...))" block, but then we could reach pte_offset_map_lock() with transhuge pages not just for file mappings but also for anonymous mappings - which would probably be fine but I think is not necessarily expected.

Link: https://lkml.kernel.org/r/20240813-uffd-thp-flip-fix-v2-2-5efa61078a41@googl... Fixes: 1d65b771bc08 ("mm/khugepaged: retract_page_tables() without mmap or vma lock") Signed-off-by: Jann Horn jannh@google.com Reviewed-by: Qi Zheng zhengqi.arch@bytedance.com Acked-by: David Hildenbrand david@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Pavel Emelyanov xemul@virtuozzo.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Conflicts: mm/userfaultfd.c [ Context conflict with userswap feature. ] Signed-off-by: Liu Shixin liushixin2@huawei.com --- mm/userfaultfd.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index b7562e6847b2..2c71a269a52c 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -724,9 +724,10 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm, err = -EFAULT; break; } - - BUG_ON(pmd_none(*dst_pmd)); - BUG_ON(pmd_trans_huge(*dst_pmd)); + /* + * For shmem mappings, khugepaged is allowed to remove page + * tables under us; pte_offset_map_lock() will deal with that. + */

#ifdef CONFIG_USERSWAP if (static_branch_unlikely(&userswap_enabled) &&