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mm: hugetlb: fix UAF in hugetlb_handle_userfault

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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: 1a1aad8a9b ("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>
This commit is contained in:
Liu Shixin 2022-09-23 12:21:13 +08:00 committed by Andrew Morton
parent c1b8fdae62
commit 958f32ce83
1 changed files with 17 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
mm/hugetlb.c
View File

@ -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;