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mm: hugetlb: fix UAF in hugetlb_handle_userfault

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commit 958f32ce832ba781ac20e11bb2d12a9352ea28fc upstream.

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: 1a1aad8a9b7b ("userfaultfd: hugetlbfs: add userfaultfd hugetlb hook")
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reported-by: syzbot+193f9cee8638750b23cf@syzkaller.appspotmail.com
Reported-by: Liu Zixian <liuzixian4@huawei.com>
Reviewed-by: Mike 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Liu Shixin 2022-09-23 12:21:13 +08:00 committed by Greg Kroah-Hartman
parent 98aada6e22
commit 0db2efb3bf
1 changed files with 17 additions and 20 deletions
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37
mm/hugetlb.c
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@ -4844,7 +4844,6 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma,
unsigned long haddr,
unsigned long reason)
{
vm_fault_t ret;
u32 hash;
struct vm_fault vmf = {
.vma = vma,
@ -4861,18 +4860,14 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma,
};
/*
* hugetlb_fault_mutex and i_mmap_rwsem 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 will be dropped during handling
* userfault, any vma operation should be careful from here.
*/
hash = hugetlb_fault_mutex_hash(mapping, idx);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
ret = handle_userfault(&vmf, reason);
i_mmap_lock_read(mapping);
mutex_lock(&hugetlb_fault_mutex_table[hash]);
return ret;
return handle_userfault(&vmf, reason);
}
static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
@ -4889,6 +4884,7 @@ 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
@ -4898,7 +4894,7 @@ 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;
}
/*
@ -4915,12 +4911,10 @@ retry:
page = find_lock_page(mapping, idx);
if (!page) {
/* 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,
VM_UFFD_MISSING);
goto out;
}
page = alloc_huge_page(vma, haddr, 0);
if (IS_ERR(page)) {
@ -4980,10 +4974,9 @@ retry:
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,
VM_UFFD_MINOR);
goto out;
}
}
@ -5034,6 +5027,8 @@ retry:
unlock_page(page);
out:
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
return ret;
backout:
@ -5131,10 +5126,12 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
mutex_lock(&hugetlb_fault_mutex_table[hash]);
entry = huge_ptep_get(ptep);
if (huge_pte_none(entry)) {
ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep, flags);
goto out_mutex;
}
if (huge_pte_none(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, flags);
ret = 0;