Commit 958f32ce authored by Liu Shixin's avatar Liu Shixin Committed by Andrew Morton
Browse files

mm: hugetlb: fix UAF in hugetlb_handle_userfault 

The vma_lock and hugetlb_fault_mutex are dropped before handling userfault
and reacquire them again after handle_userfault(), but reacquire the
vma_lock could lead to UAF[1,2] due to the following race,

hugetlb_fault
  hugetlb_no_page
    /*unlock vma_lock */
    hugetlb_handle_userfault
      handle_userfault
        /* unlock mm->mmap_lock*/
                                           vm_mmap_pgoff
                                             do_mmap
                                               mmap_region
                                                 munmap_vma_range
                                                   /* clean old vma */
        /* lock vma_lock again  <--- UAF */
    /* unlock vma_lock */

Since the vma_lock will unlock immediately after
hugetlb_handle_userfault(), let's drop the unneeded lock and unlock in
hugetlb_handle_userfault() to fix the issue.

[1] https://lore.kernel.org/linux-mm/000000000000d5e00a05e834962e@google.com/
[2] https://lore.kernel.org/linux-mm/20220921014457.1668-1-liuzixian4@huawei.com/
Link: https://lkml.kernel.org/r/20220923042113.137273-1-liushixin2@huawei.com


Fixes: 1a1aad8a ("userfaultfd: hugetlbfs: add userfaultfd hugetlb hook")
Signed-off-by: default avatarLiu Shixin <liushixin2@huawei.com>
Signed-off-by: default avatarKefeng Wang <wangkefeng.wang@huawei.com>
Reported-by: default avatar <syzbot+193f9cee8638750b23cf@syzkaller.appspotmail.com>
Reported-by: default avatarLiu Zixian <liuzixian4@huawei.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: <stable@vger.kernel.org>	[4.14+]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent c1b8fdae

mm/hugetlb.c

+17 −20
Original line number Diff line number Diff line
@@ -5489,7 +5489,6 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma, 
						  unsigned long addr,

						  unsigned long reason)

{

	vm_fault_t ret;

	u32 hash;

	struct vm_fault vmf = {

		.vma = vma,
@@ -5507,18 +5506,14 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma, 
	};



	/*

	 * vma_lock and hugetlb_fault_mutex must be

	 * dropped before handling userfault.  Reacquire

	 * after handling fault to make calling code simpler.

	 * vma_lock and hugetlb_fault_mutex must be dropped before handling

	 * userfault. Also mmap_lock could be dropped due to handling

	 * userfault, any vma operation should be careful from here.

	 */

	hugetlb_vma_unlock_read(vma);

	hash = hugetlb_fault_mutex_hash(mapping, idx);

	mutex_unlock(&hugetlb_fault_mutex_table[hash]);

	ret = handle_userfault(&vmf, reason);

	mutex_lock(&hugetlb_fault_mutex_table[hash]);

	hugetlb_vma_lock_read(vma);



	return ret;

	return handle_userfault(&vmf, reason);

}



static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
@@ -5536,6 +5531,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, 
	spinlock_t *ptl;

	unsigned long haddr = address & huge_page_mask(h);

	bool new_page, new_pagecache_page = false;

	u32 hash = hugetlb_fault_mutex_hash(mapping, idx);



	/*

	 * Currently, we are forced to kill the process in the event the
@@ -5546,7 +5542,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, 
	if (is_vma_resv_set(vma, HPAGE_RESV_UNMAPPED)) {

		pr_warn_ratelimited("PID %d killed due to inadequate hugepage pool\n",

			   current->pid);

		return ret;

		goto out;

	}



	/*
@@ -5560,12 +5556,10 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, 
		if (idx >= size)

			goto out;

		/* Check for page in userfault range */

		if (userfaultfd_missing(vma)) {

			ret = hugetlb_handle_userfault(vma, mapping, idx,

		if (userfaultfd_missing(vma))

			return hugetlb_handle_userfault(vma, mapping, idx,

						       flags, haddr, address,

						       VM_UFFD_MISSING);

			goto out;

		}



		page = alloc_huge_page(vma, haddr, 0);

		if (IS_ERR(page)) {
@@ -5631,10 +5625,9 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, 
		if (userfaultfd_minor(vma)) {

			unlock_page(page);

			put_page(page);

			ret = hugetlb_handle_userfault(vma, mapping, idx,

			return hugetlb_handle_userfault(vma, mapping, idx,

						       flags, haddr, address,

						       VM_UFFD_MINOR);

			goto out;

		}

	}
@@ -5692,6 +5685,8 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, 


	unlock_page(page);

out:

	hugetlb_vma_unlock_read(vma);

	mutex_unlock(&hugetlb_fault_mutex_table[hash]);

	return ret;



backout:
@@ -5789,11 +5784,13 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, 


	entry = huge_ptep_get(ptep);

	/* PTE markers should be handled the same way as none pte */

	if (huge_pte_none_mostly(entry)) {

		ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep,

	if (huge_pte_none_mostly(entry))

		/*

		 * hugetlb_no_page will drop vma lock and hugetlb fault

		 * mutex internally, which make us return immediately.

		 */

		return hugetlb_no_page(mm, vma, mapping, idx, address, ptep,

				      entry, flags);

		goto out_mutex;

	}



	ret = 0;