The memory mapping of a process may change between #PF event and the call
to mcopy_atomic that comes to resolve the page fault. In such case, there
will be no VMA covering the range passed to mcopy_atomic or the VMA will
not have userfaultfd context.
To allow uffd monitor to distinguish those case from other errors, let's
return -ENOENT instead of -EINVAL.
Note, that despite availability of UFFD_EVENT_UNMAP there still might be
race between the processing of UFFD_EVENT_UNMAP and outstanding
mcopy_atomic in case of non-cooperative uffd usage.
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
mm/userfaultfd.c | 42 ++++++++++++++++++++++--------------------
1 file changed, 22 insertions(+), 20 deletions(-)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index a0817cc..b861cf9 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -195,11 +195,18 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
* retry, dst_vma will be set to NULL and we must lookup again.
*/
if (!dst_vma) {
- err = -EINVAL;
+ err = -ENOENT;
dst_vma = find_vma(dst_mm, dst_start);
if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
goto out_unlock;
+ /*
+ * Only allow __mcopy_atomic_hugetlb on userfaultfd
+ * registered ranges.
+ */
+ if (!dst_vma->vm_userfaultfd_ctx.ctx)
+ goto out_unlock;
+ err = -EINVAL;
if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
goto out_unlock;
@@ -219,12 +226,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
goto out_unlock;
/*
- * Only allow __mcopy_atomic_hugetlb on userfaultfd registered ranges.
- */
- if (!dst_vma->vm_userfaultfd_ctx.ctx)
- goto out_unlock;
-
- /*
* Ensure the dst_vma has a anon_vma.
*/
err = -ENOMEM;
@@ -368,10 +369,23 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
* Make sure the vma is not shared, that the dst range is
* both valid and fully within a single existing vma.
*/
- err = -EINVAL;
+ err = -ENOENT;
dst_vma = find_vma(dst_mm, dst_start);
if (!dst_vma)
goto out_unlock;
+ /*
+ * Be strict and only allow __mcopy_atomic on userfaultfd
+ * registered ranges to prevent userland errors going
+ * unnoticed. As far as the VM consistency is concerned, it
+ * would be perfectly safe to remove this check, but there's
+ * no useful usage for __mcopy_atomic ouside of userfaultfd
+ * registered ranges. This is after all why these are ioctls
+ * belonging to the userfaultfd and not syscalls.
+ */
+ if (!dst_vma->vm_userfaultfd_ctx.ctx)
+ goto out_unlock;
+
+ err = -EINVAL;
if (!vma_is_shmem(dst_vma) && dst_vma->vm_flags & VM_SHARED)
goto out_unlock;
if (dst_start < dst_vma->vm_start ||
@@ -385,18 +399,6 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
return __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
src_start, len, zeropage);
- /*
- * Be strict and only allow __mcopy_atomic on userfaultfd
- * registered ranges to prevent userland errors going
- * unnoticed. As far as the VM consistency is concerned, it
- * would be perfectly safe to remove this check, but there's
- * no useful usage for __mcopy_atomic ouside of userfaultfd
- * registered ranges. This is after all why these are ioctls
- * belonging to the userfaultfd and not syscalls.
- */
- if (!dst_vma->vm_userfaultfd_ctx.ctx)
- goto out_unlock;
-
if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
goto out_unlock;
--
1.9.1
--
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