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-rw-r--r--mm/mremap.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/mm/mremap.c b/mm/mremap.c
index 3f23715d3c69..7395564daa6c 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -384,6 +384,19 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
if (!vma || vma->vm_start > addr)
return ERR_PTR(-EFAULT);
+ /*
+ * !old_len is a special case where an attempt is made to 'duplicate'
+ * a mapping. This makes no sense for private mappings as it will
+ * instead create a fresh/new mapping unrelated to the original. This
+ * is contrary to the basic idea of mremap which creates new mappings
+ * based on the original. There are no known use cases for this
+ * behavior. As a result, fail such attempts.
+ */
+ if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
+ pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap. This is not supported.\n", current->comm, current->pid);
+ return ERR_PTR(-EINVAL);
+ }
+
if (is_vm_hugetlb_page(vma))
return ERR_PTR(-EINVAL);