[PATCH 5.19 699/717] mm: hugetlb: fix UAF in hugetlb_handle_userfault

Greg Kroah-Hartman
2022-10-22T08:46:14Z

From: Liu Shixin <liushixin2@huawei.com>

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>
---
mm/hugetlb.c | 37 +++++++++++++++++--------------------
1 file changed, 17 insertions(+), 20 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5467,7 +5467,6 @@ static inline vm_fault_t hugetlb_handle_
unsigned long addr,
unsigned long reason)
{
- vm_fault_t ret;
u32 hash;
struct vm_fault vmf = {
.vma = vma,
@@ -5485,18 +5484,14 @@ static inline vm_fault_t hugetlb_handle_
};

/*
- * 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,
@@ -5514,6 +5509,7 @@ static vm_fault_t hugetlb_no_page(struct
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
@@ -5524,7 +5520,7 @@ static vm_fault_t hugetlb_no_page(struct
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;
}

/*
@@ -5541,12 +5537,10 @@ 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, address,
VM_UFFD_MISSING);
- goto out;
- }

page = alloc_huge_page(vma, haddr, 0);
if (IS_ERR(page)) {
@@ -5606,10 +5600,9 @@ 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, address,
VM_UFFD_MINOR);
- goto out;
}
}

@@ -5667,6 +5660,8 @@ retry:

unlock_page(page);
out:
+ mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+ i_mmap_unlock_read(mapping);
return ret;

backout:
@@ -5765,11 +5760,13 @@ vm_fault_t hugetlb_fault(struct mm_struc

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;