The patch titled
Subject: mm: hugetlb: fix UAF in hugetlb_handle_userfault
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-hugetlb-fix-uaf-in-hugetlb_handle_userfault.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-fix-uaf-in-hugetlb_handle_userfault.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Liu Shixin <liushixin2@xxxxxxxxxx>
Subject: mm: hugetlb: fix UAF in hugetlb_handle_userfault
Date: Sat, 24 Sep 2022 11:49:05 +0800
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/20220924034905.2694686-1-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>
---
--- a/mm/hugetlb.c~mm-hugetlb-fix-uaf-in-hugetlb_handle_userfault
+++ a/mm/hugetlb.c
@@ -5478,7 +5478,6 @@ 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,
@@ -5496,18 +5495,14 @@ 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,
@@ -5525,6 +5520,7 @@ 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
@@ -5535,7 +5531,7 @@ 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;
}
/*
@@ -5552,12 +5548,10 @@ 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)) {
@@ -5617,10 +5611,9 @@ 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;
}
}
@@ -5678,6 +5671,8 @@ retry:
unlock_page(page);
out:
+ mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+ i_mmap_unlock_read(mapping);
return ret;
backout:
@@ -5776,11 +5771,13 @@ 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;
_
Patches currently in -mm which might be from liushixin2@xxxxxxxxxx are
mm-hugetlb-fix-uaf-in-hugetlb_handle_userfault.patch
mm-shuffle-convert-module_param_call-to-module_param_cb.patch
mm-kfence-convert-to-define_seq_attribute.patch
mm-huge_memory-prevent-thp_zero_page_alloc-increased-twice.patch
mm-memcontrol-use-kstrtobool-for-swapaccount-param-parsing.patch
