rmap: fix anon_vma_fork() memory leak

Fix a memory leak in anon_vma_fork(), where we fail to tear down the
anon_vmas attached to the new VMA in case setting up the new anon_vma
fails.

This bug also has the potential to leave behind anon_vma_chain structs
with pointers to invalid memory.
Reported-by: NMinchan Kim <minchan.kim@gmail.com>
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/rmap.c

@@ -232,6 +232,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
  out_error_free_anon_vma:
 	anon_vma_free(anon_vma);
  out_error:
+	unlink_anon_vmas(vma);
 	return -ENOMEM;
 }