nommu: pass NULL argument to vma_iter_prealloc()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nommu: pass NULL argument to vma_iter_prealloc() When deleting a vma entry from a maple tree, it has to pass NULL to vma_iter_prealloc() in order to calculate internal state of the tree, but it passed a wrong argument. As a result, nommu kernels crashed upon accessing a vma iterator, such as acct_collect() reading the size of vma entries after do_munmap(). This commit fixes this issue by passing a right argument to the preallocation call.

References

• https://git.kernel.org/stable/c/8bbf0ab631cdf1dade6745f137cff98751e6ced7
• https://git.kernel.org/stable/c/aceaf33b7666b72dfb86e0aa977be81e3bcbc727
• https://git.kernel.org/stable/c/247d720b2c5d22f7281437fd6054a138256986ba