[PATCH 5.15 516/530] mm: hugetlb: fix UAF in hugetlb_handle_userfault

[Greg Kroah-Hartman]

From: Liu Shixin <liushixin2@xxxxxxxxxx>

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@xxxxxxxxxx/
[2] https://lore.kernel.org/linux-mm/20220921014457.1668-1-liuzixian4@xxxxxxxxxx/
Link: https://lkml.kernel.org/r/20220923042113.137273-1-liushixin2@xxxxxxxxxx
Fixes: 1a1aad8a9b7b ("userfaultfd: hugetlbfs: add userfaultfd hugetlb hook")
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Reported-by: syzbot+193f9cee8638750b23cf@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Liu Zixian <liuzixian4@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>	[4.14+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/hugetlb.c |   37 +++++++++++++++++--------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4844,7 +4844,6 @@ static inline vm_fault_t hugetlb_handle_
 						  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_
 	};
 
 	/*
-	 * 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
 	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
 	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_struc
 	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;