| Message ID | 20200722121439.44328-1-kirill.shutemov@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | khugepaged: Fix null-pointer dereference due to race | expand |
On 22.07.20 14:14, Kirill A. Shutemov wrote: > khugepaged has to drop mmap lock several times while collapsing a page. > The situation can change while the lock is dropped and we need to > re-validate that the VMA is still in place and the PMD is still subject > for collapse. > > But we miss one corner case: while collapsing an anonymous pages the VMA > could be replaced with file VMA. If the file VMA doesn't have any > private pages we get NULL pointer dereference: > > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] > anon_vma_lock_write include/linux/rmap.h:120 [inline] > collapse_huge_page mm/khugepaged.c:1110 [inline] > khugepaged_scan_pmd mm/khugepaged.c:1349 [inline] > khugepaged_scan_mm_slot mm/khugepaged.c:2110 [inline] > khugepaged_do_scan mm/khugepaged.c:2193 [inline] > khugepaged+0x3bba/0x5a10 mm/khugepaged.c:2238 > > The fix is to make sure that the VMA is anonymous in > hugepage_vma_revalidate(). The helper is only used for collapsing > anonymous pages. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > Reported-by: syzbot+ed318e8b790ca72c5ad0@syzkaller.appspotmail.com > --- > mm/khugepaged.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index b043c40a21d4..700f5160f3e4 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -958,6 +958,9 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, > return SCAN_ADDRESS_RANGE; > if (!hugepage_vma_check(vma, vma->vm_flags)) > return SCAN_VMA_CHECK; > + /* Anon VMA expected */ > + if (!vma->anon_vma || vma->vm_ops) > + return SCAN_VMA_CHECK; > return 0; > } > > LGTM Reviewed-by: David Hildenbrand <david@redhat.com>
On Wed, Jul 22, 2020 at 5:14 AM Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote: > > khugepaged has to drop mmap lock several times while collapsing a page. > The situation can change while the lock is dropped and we need to > re-validate that the VMA is still in place and the PMD is still subject > for collapse. > > But we miss one corner case: while collapsing an anonymous pages the VMA > could be replaced with file VMA. If the file VMA doesn't have any > private pages we get NULL pointer dereference: > > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] > anon_vma_lock_write include/linux/rmap.h:120 [inline] > collapse_huge_page mm/khugepaged.c:1110 [inline] > khugepaged_scan_pmd mm/khugepaged.c:1349 [inline] > khugepaged_scan_mm_slot mm/khugepaged.c:2110 [inline] > khugepaged_do_scan mm/khugepaged.c:2193 [inline] > khugepaged+0x3bba/0x5a10 mm/khugepaged.c:2238 > > The fix is to make sure that the VMA is anonymous in > hugepage_vma_revalidate(). The helper is only used for collapsing > anonymous pages. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > Reported-by: syzbot+ed318e8b790ca72c5ad0@syzkaller.appspotmail.com Acked-by: Yang Shi <yang.shi@linux.alibaba.com> I think this is worth backporting to stable as well. > --- > mm/khugepaged.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index b043c40a21d4..700f5160f3e4 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -958,6 +958,9 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, > return SCAN_ADDRESS_RANGE; > if (!hugepage_vma_check(vma, vma->vm_flags)) > return SCAN_VMA_CHECK; > + /* Anon VMA expected */ > + if (!vma->anon_vma || vma->vm_ops) > + return SCAN_VMA_CHECK; > return 0; > } > > -- > 2.26.2 > >
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index b043c40a21d4..700f5160f3e4 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -958,6 +958,9 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, return SCAN_ADDRESS_RANGE; if (!hugepage_vma_check(vma, vma->vm_flags)) return SCAN_VMA_CHECK; + /* Anon VMA expected */ + if (!vma->anon_vma || vma->vm_ops) + return SCAN_VMA_CHECK; return 0; }
khugepaged has to drop mmap lock several times while collapsing a page. The situation can change while the lock is dropped and we need to re-validate that the VMA is still in place and the PMD is still subject for collapse. But we miss one corner case: while collapsing an anonymous pages the VMA could be replaced with file VMA. If the file VMA doesn't have any private pages we get NULL pointer dereference: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] anon_vma_lock_write include/linux/rmap.h:120 [inline] collapse_huge_page mm/khugepaged.c:1110 [inline] khugepaged_scan_pmd mm/khugepaged.c:1349 [inline] khugepaged_scan_mm_slot mm/khugepaged.c:2110 [inline] khugepaged_do_scan mm/khugepaged.c:2193 [inline] khugepaged+0x3bba/0x5a10 mm/khugepaged.c:2238 The fix is to make sure that the VMA is anonymous in hugepage_vma_revalidate(). The helper is only used for collapsing anonymous pages. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Reported-by: syzbot+ed318e8b790ca72c5ad0@syzkaller.appspotmail.com --- mm/khugepaged.c | 3 +++ 1 file changed, 3 insertions(+)