From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:39100 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751141AbdK0IeA (ORCPT ); Mon, 27 Nov 2017 03:34:00 -0500 Subject: Patch "x86/mm: fix use-after-free of vma during userfaultfd fault" has been added to the 4.9-stable tree To: vbabka@suse.cz, aarcange@redhat.com, bot+6a5269ce759a7bb12754ed9622076dc93f65a1f6@syzkaller.appspotmail.com, dvyukov@google.com, ebiggers3@gmail.com, gregkh@linuxfoundation.org, kirill@shutemov.name, torvalds@linux-foundation.org Cc: , From: Date: Mon, 27 Nov 2017 09:34:04 +0100 Message-ID: <15117716446578@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled x86/mm: fix use-after-free of vma during userfaultfd fault to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-mm-fix-use-after-free-of-vma-during-userfaultfd-fault.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From cb0631fd3cf9e989cd48293fe631cbc402aec9a9 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Wed, 1 Nov 2017 08:21:25 +0100 Subject: x86/mm: fix use-after-free of vma during userfaultfd fault From: Vlastimil Babka commit cb0631fd3cf9e989cd48293fe631cbc402aec9a9 upstream. Syzkaller with KASAN has reported a use-after-free of vma->vm_flags in __do_page_fault() with the following reproducer: mmap(&(0x7f0000000000/0xfff000)=nil, 0xfff000, 0x3, 0x32, 0xffffffffffffffff, 0x0) mmap(&(0x7f0000011000/0x3000)=nil, 0x3000, 0x1, 0x32, 0xffffffffffffffff, 0x0) r0 = userfaultfd(0x0) ioctl$UFFDIO_API(r0, 0xc018aa3f, &(0x7f0000002000-0x18)={0xaa, 0x0, 0x0}) ioctl$UFFDIO_REGISTER(r0, 0xc020aa00, &(0x7f0000019000)={{&(0x7f0000012000/0x2000)=nil, 0x2000}, 0x1, 0x0}) r1 = gettid() syz_open_dev$evdev(&(0x7f0000013000-0x12)="2f6465762f696e7075742f6576656e742300", 0x0, 0x0) tkill(r1, 0x7) The vma should be pinned by mmap_sem, but handle_userfault() might (in a return to userspace scenario) release it and then acquire again, so when we return to __do_page_fault() (with other result than VM_FAULT_RETRY), the vma might be gone. Specifically, per Andrea the scenario is "A return to userland to repeat the page fault later with a VM_FAULT_NOPAGE retval (potentially after handling any pending signal during the return to userland). The return to userland is identified whenever FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in vmf->flags" However, since commit a3c4fb7c9c2e ("x86/mm: Fix fault error path using unsafe vma pointer") there is a vma_pkey() read of vma->vm_flags after that point, which can thus become use-after-free. Fix this by moving the read before calling handle_mm_fault(). Reported-by: syzbot Reported-by: Dmitry Vyukov Suggested-by: Kirill A. Shutemov Fixes: 3c4fb7c9c2e ("x86/mm: Fix fault error path using unsafe vma pointer") Reviewed-by: Andrea Arcangeli Signed-off-by: Vlastimil Babka Signed-off-by: Linus Torvalds Cc: Eric Biggers Signed-off-by: Greg Kroah-Hartman --- arch/x86/mm/fault.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1393,7 +1393,17 @@ good_area: * make sure we exit gracefully rather than endlessly redo * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked. + * + * Note that handle_userfault() may also release and reacquire mmap_sem + * (and not return with VM_FAULT_RETRY), when returning to userland to + * repeat the page fault later with a VM_FAULT_NOPAGE retval + * (potentially after handling any pending signal during the return to + * userland). The return to userland is identified whenever + * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags. + * Thus we have to be careful about not touching vma after handling the + * fault, so we read the pkey beforehand. */ + pkey = vma_pkey(vma); fault = handle_mm_fault(vma, address, flags); major |= fault & VM_FAULT_MAJOR; @@ -1420,7 +1430,6 @@ good_area: return; } - pkey = vma_pkey(vma); up_read(&mm->mmap_sem); if (unlikely(fault & VM_FAULT_ERROR)) { mm_fault_error(regs, error_code, address, &pkey, fault); Patches currently in stable-queue which might be from vbabka@suse.cz are queue-4.9/x86-mm-fix-use-after-free-of-vma-during-userfaultfd-fault.patch