From 6c21e066f9256ea1df6f88768f6ae1080b7cf509 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Fri, 28 Jul 2023 06:13:21 +0200 Subject: mm/mempolicy: Take VMA lock before replacing policy mbind() calls down into vma_replace_policy() without taking the per-VMA locks, replaces the VMA's vma->vm_policy pointer, and frees the old policy. That's bad; a concurrent page fault might still be using the old policy (in vma_alloc_folio()), resulting in use-after-free. Normally this will manifest as a use-after-free read first, but it can result in memory corruption, including because vma_alloc_folio() can call mpol_cond_put() on the freed policy, which conditionally changes the policy's refcount member. This bug is specific to CONFIG_NUMA, but it does also affect non-NUMA systems as long as the kernel was built with CONFIG_NUMA. Signed-off-by: Jann Horn Reviewed-by: Suren Baghdasaryan Fixes: 5e31275cc997 ("mm: add per-VMA lock and helper functions to control it") Cc: stable@kernel.org Signed-off-by: Linus Torvalds --- mm/mempolicy.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) (limited to 'mm') diff --git a/mm/mempolicy.c b/mm/mempolicy.c index edc25195f5bd..c53f8beeb507 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -384,8 +384,10 @@ void mpol_rebind_mm(struct mm_struct *mm, nodemask_t *new) VMA_ITERATOR(vmi, mm, 0); mmap_write_lock(mm); - for_each_vma(vmi, vma) + for_each_vma(vmi, vma) { + vma_start_write(vma); mpol_rebind_policy(vma->vm_policy, new); + } mmap_write_unlock(mm); } @@ -768,6 +770,8 @@ static int vma_replace_policy(struct vm_area_struct *vma, struct mempolicy *old; struct mempolicy *new; + vma_assert_write_locked(vma); + pr_debug("vma %lx-%lx/%lx vm_ops %p vm_file %p set_policy %p\n", vma->vm_start, vma->vm_end, vma->vm_pgoff, vma->vm_ops, vma->vm_file, @@ -1313,6 +1317,14 @@ static long do_mbind(unsigned long start, unsigned long len, if (err) goto mpol_out; + /* + * Lock the VMAs before scanning for pages to migrate, to ensure we don't + * miss a concurrently inserted page. + */ + vma_iter_init(&vmi, mm, start); + for_each_vma_range(vmi, vma, end) + vma_start_write(vma); + ret = queue_pages_range(mm, start, end, nmask, flags | MPOL_MF_INVERT, &pagelist); @@ -1538,6 +1550,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le break; } + vma_start_write(vma); new->home_node = home_node; err = mbind_range(&vmi, vma, &prev, start, end, new); mpol_put(new); -- cgit v1.2.3-58-ga151