From: Lokesh Gidra lokeshgidra@google.com
In mfill_atomic_hugetlb(), mmap_changing isn't being checked again if we drop mmap_lock and reacquire it. When the lock is not held, mmap_changing could have been incremented. This is also inconsistent with the behavior in mfill_atomic().
Link: https://lkml.kernel.org/r/20240117223729.1444522-1-lokeshgidra@google.com Fixes: df2cc96e77011 ("userfaultfd: prevent non-cooperative events vs mcopy_atomic races") Signed-off-by: Lokesh Gidra lokeshgidra@google.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Mike Rapoport rppt@kernel.org Cc: Axel Rasmussen axelrasmussen@google.com Cc: Brian Geffon bgeffon@google.com Cc: David Hildenbrand david@redhat.com Cc: Jann Horn jannh@google.com Cc: Kalesh Singh kaleshsingh@google.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Nicolas Geoffray ngeoffray@google.com Cc: Peter Xu peterx@redhat.com Cc: Suren Baghdasaryan surenb@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit 67695f18d55924b2013534ef3bdc363bc9e14605) Signed-off-by: Mike Rapoport (IBM) rppt@kernel.org --- mm/userfaultfd.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 6fa66e2111ea..e8758304a9f3 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -177,6 +177,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, unsigned long dst_start, unsigned long src_start, unsigned long len, + bool *mmap_changing, bool zeropage) { int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED; @@ -308,6 +309,15 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, goto out; } down_read(&dst_mm->mmap_sem); + /* + * If memory mappings are changing because of non-cooperative + * operation (e.g. mremap) running in parallel, bail out and + * request the user to retry later + */ + if (mmap_changing && READ_ONCE(*mmap_changing)) { + err = -EAGAIN; + break; + }
dst_vma = NULL; goto retry; @@ -389,6 +399,7 @@ extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, unsigned long dst_start, unsigned long src_start, unsigned long len, + bool *mmap_changing, bool zeropage); #endif /* CONFIG_HUGETLB_PAGE */
@@ -506,7 +517,8 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm, */ if (is_vm_hugetlb_page(dst_vma)) return __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start, - src_start, len, zeropage); + src_start, len, mmap_changing, + zeropage);
if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) goto out_unlock;