linux-kernel - [PATCH 5.10 380/390] mm: hugetlb: fix UAF in hugetlb_handle

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Message-Id: <20221024113039.156393036@linuxfoundation.org>
Date:   Mon, 24 Oct 2022 13:32:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Liu Shixin <liushixin2@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        syzbot+193f9cee8638750b23cf@...kaller.appspotmail.com,
        Liu Zixian <liuzixian4@...wei.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Muchun Song <songmuchun@...edance.com>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 5.10 380/390] mm: hugetlb: fix UAF in hugetlb_handle_userfault

From: Liu Shixin <liushixin2@...wei.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@...wei.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
Reported-by: syzbot+193f9cee8638750b23cf@...kaller.appspotmail.com
Reported-by: Liu Zixian <liuzixian4@...wei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Muchun Song <songmuchun@...edance.com>
Cc: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc: <stable@...r.kernel.org>	[4.14+]
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/hugetlb.c |   29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4337,6 +4337,7 @@ static vm_fault_t hugetlb_no_page(struct
 	spinlock_t *ptl;
 	unsigned long haddr = address & huge_page_mask(h);
 	bool new_page = false;
+	u32 hash = hugetlb_fault_mutex_hash(mapping, idx);
 
 	/*
 	 * Currently, we are forced to kill the process in the event the
@@ -4346,7 +4347,7 @@ 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;
 	}
 
 	/*
@@ -4365,7 +4366,6 @@ retry:
 		 * Check for page in userfault range
 		 */
 		if (userfaultfd_missing(vma)) {
-			u32 hash;
 			struct vm_fault vmf = {
 				.vma = vma,
 				.address = haddr,
@@ -4380,17 +4380,14 @@ retry:
 			};
 
 			/*
-			 * 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, VM_UFFD_MISSING);
-			i_mmap_lock_read(mapping);
-			mutex_lock(&hugetlb_fault_mutex_table[hash]);
-			goto out;
+			return handle_userfault(&vmf, VM_UFFD_MISSING);
 		}
 
 		page = alloc_huge_page(vma, haddr, 0);
@@ -4497,6 +4494,8 @@ retry:
 
 	unlock_page(page);
 out:
+	mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+	i_mmap_unlock_read(mapping);
 	return ret;
 
 backout:
@@ -4592,10 +4591,12 @@ 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;