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/
Reported-by: syzbot+193f9cee8638750b23cf@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Liu Zixian <liuzixian4@xxxxxxxxxx>
Fixes: 1a1aad8a9b7b ("userfaultfd: hugetlbfs: add userfaultfd hugetlb hook")
CC: stable@xxxxxxxxxxxxxxx # 4.14+
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/hugetlb.c | 29 +++++++++++++++--------------
1 file changed, 15 insertions(+), 14 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c42c76447e10..c57c165bfbbc 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4337,6 +4337,7 @@ 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 = 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 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;
}
/*
@@ -4365,7 +4366,6 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
* Check for page in userfault range
*/
if (userfaultfd_missing(vma)) {
- u32 hash;
struct vm_fault vmf = {
.vma = vma,
.address = haddr,
@@ -4380,17 +4380,14 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
};
/*
- * 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 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
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_struct *mm, struct vm_area_struct *vma,
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;
--
2.25.1
