mm anon rmap: in mremap, set the new vma's position before anon_vma_clone()

anon_vma_clone() expects new_vma->vm_{start,end,pgoff} to be correctly set
so that the new vma can be indexed on the anon interval tree.

copy_vma() was failing to do that, which broke mremap().
Signed-off-by: NMichel Lespinasse <walken@google.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Tested-by: NSasha Levin <levinsasha928@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -2419,16 +2419,16 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 		new_vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 		if (new_vma) {
 			*new_vma = *vma;
+			new_vma->vm_start = addr;
+			new_vma->vm_end = addr + len;
+			new_vma->vm_pgoff = pgoff;
 			pol = mpol_dup(vma_policy(vma));
 			if (IS_ERR(pol))
 				goto out_free_vma;
+			vma_set_policy(new_vma, pol);
 			INIT_LIST_HEAD(&new_vma->anon_vma_chain);
 			if (anon_vma_clone(new_vma, vma))
 				goto out_free_mempol;
-			vma_set_policy(new_vma, pol);
-			new_vma->vm_start = addr;
-			new_vma->vm_end = addr + len;
-			new_vma->vm_pgoff = pgoff;
 			if (new_vma->vm_file)
 				get_file(new_vma->vm_file);
 			if (new_vma->vm_ops && new_vma->vm_ops->open)