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Mike Rapoport (Microsoft)
85668fda93
Patch series "userfaultfd: verify VMA state across UFFDIO_COPY retry", v2. ... and two more small fixes. This patch (of 3): mfill_copy_folio_retry() drops the VMA lock for copy_from_user() and reacquires it afterwards. The destination VMA can be replaced during that window. The existing check compares vma_uffd_ops() before and after the retry, but if a shmem VMA with MAP_SHARED is replaced with a shmem VMA with MAP_PRIVATE (or vice versa) the replacement goes undetected. The change from MAP_PRIVATE to MAP_SHARED will treat the folio allocated with shmem_alloc_folio() as anonymous and this will cause BUG() when mfill_atomic_install_pte() will try to folio_add_new_anon_rmap(). The change from MAP_SHARED to MAP_PRIVATE allows injection of folios into the page cache of the original VMA. There is no need to change for hugetlb because it never uses mfill_copy_folio_retry(). Introduce helpers for more comprehensive comparison of VMA state: - mfill_retry_state_save() to save the relevant VMA state into a struct mfill_retry_state (original uffd_ops, relevant VMA flags, vm_file and pgoff) before dropping the lock - mfill_retry_state_changed() to compare the saved state with the state of the VMA acquired after retaking the locks - mfill_retry_state_put() to release vm_file pinning. Use DEFINE_FREE() cleanup to wrap mfill_retry_state_put() to avoid complicating error handling paths in mfill_copy_folio_retry(). Link: https://lore.kernel.org/20260527184751.4147364-1-rppt@kernel.org Link: https://lore.kernel.org/20260527184751.4147364-2-rppt@kernel.org Fixes:292411fda2("mm/userfaultfd: detect VMA type change after copy retry in mfill_copy_folio_retry()") Fixes:6ab703034f("userfaultfd: mfill_atomic(): remove retry logic") Co-developed-by: Michael Bommarito <michael.bommarito@gmail.com> Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Suggested-by: Peter Xu <peterx@redhat.com> Co-developed-by: David Carlier <devnexen@gmail.com> Signed-off-by: David Carlier <devnexen@gmail.com> Reviewed-by: Lorenzo Stoakes <ljs@kernel.org> Cc: David Hildenbrand <david@kernel.org> Cc: Liam R. Howlett <liam@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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