mremap will create a 'duplicate' mapping if old_size == 0 is
specified. Such duplicate mappings make no sense for private
mappings. If duplication is attempted for a private mapping,
mremap creates a separate private mapping unrelated to the
original mapping and makes no modifications to the original.
This is contrary to the purpose of mremap which should return
a mapping which is in some way related to the original.
Therefore, return EINVAL in the case where if an attempt is
made to duplicate a private mapping. Also, print a warning
message (once) if such an attempt is made.
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/mremap.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/mm/mremap.c b/mm/mremap.c
index cd8a1b1..949f6a7 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -383,6 +383,15 @@ 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 a mapping is 'duplicated'.
+ * Do not allow this for private mappings.
+ */
+ 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);
--
2.7.5
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