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 @@ -5482,7 +5482,6 @@ 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, @@ -5500,18 +5499,14 @@ 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, @@ -5529,6 +5524,7 @@ 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 @@ -5539,7 +5535,7 @@ 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; }
/* @@ -5556,12 +5552,10 @@ 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)) { @@ -5621,10 +5615,9 @@ 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; } }
@@ -5682,6 +5675,8 @@ retry:
unlock_page(page); out: + mutex_unlock(&hugetlb_fault_mutex_table[hash]); + i_mmap_unlock_read(mapping); return ret;
backout: @@ -5780,11 +5775,13 @@ 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;