From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBCEBC56202 for ; Mon, 23 Nov 2020 12:33:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A86B20721 for ; Mon, 23 Nov 2020 12:33:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Oje1MLwt" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730675AbgKWMdu (ORCPT ); Mon, 23 Nov 2020 07:33:50 -0500 Received: from mail.kernel.org ([198.145.29.99]:44924 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731240AbgKWMde (ORCPT ); Mon, 23 Nov 2020 07:33:34 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 153D32065E; Mon, 23 Nov 2020 12:33:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1606134813; bh=PwLfbBqgGzz6Ly0Nf8aQXizElWKPdsHNO1kb7/SjCH8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Oje1MLwtR8CHeJgKThmx4IBADCfRmfk6jqfXNwFVLGeB5KrYsmCpNHnJyxagCoVeN RkpErFXgGYQyS0vBxwiu5HK+PfgD3IM1diKO+YN5ncOQ4nwfQpBVUurVg+rNAujLL0 AZxj2zM6zlKff68fkBq3F+MyxtOGyO5Ov3rgaR+Q= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Alexander Egorenkov , Gerald Schaefer , Andrew Morton , Andrea Arcangeli , Heiko Carstens , Linus Torvalds Subject: [PATCH 4.19 91/91] mm/userfaultfd: do not access vma->vm_mm after calling handle_userfault() Date: Mon, 23 Nov 2020 13:22:51 +0100 Message-Id: <20201123121813.744695905@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201123121809.285416732@linuxfoundation.org> References: <20201123121809.285416732@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Gerald Schaefer commit bfe8cc1db02ab243c62780f17fc57f65bde0afe1 upstream. Alexander reported a syzkaller / KASAN finding on s390, see below for complete output. In do_huge_pmd_anonymous_page(), the pre-allocated pagetable will be freed in some cases. In the case of userfaultfd_missing(), this will happen after calling handle_userfault(), which might have released the mmap_lock. Therefore, the following pte_free(vma->vm_mm, pgtable) will access an unstable vma->vm_mm, which could have been freed or re-used already. For all architectures other than s390 this will go w/o any negative impact, because pte_free() simply frees the page and ignores the passed-in mm. The implementation for SPARC32 would also access mm->page_table_lock for pte_free(), but there is no THP support in SPARC32, so the buggy code path will not be used there. For s390, the mm->context.pgtable_list is being used to maintain the 2K pagetable fragments, and operating on an already freed or even re-used mm could result in various more or less subtle bugs due to list / pagetable corruption. Fix this by calling pte_free() before handle_userfault(), similar to how it is already done in __do_huge_pmd_anonymous_page() for the WRITE / non-huge_zero_page case. Commit 6b251fc96cf2c ("userfaultfd: call handle_userfault() for userfaultfd_missing() faults") actually introduced both, the do_huge_pmd_anonymous_page() and also __do_huge_pmd_anonymous_page() changes wrt to calling handle_userfault(), but only in the latter case it put the pte_free() before calling handle_userfault(). BUG: KASAN: use-after-free in do_huge_pmd_anonymous_page+0xcda/0xd90 mm/huge_memory.c:744 Read of size 8 at addr 00000000962d6988 by task syz-executor.0/9334 CPU: 1 PID: 9334 Comm: syz-executor.0 Not tainted 5.10.0-rc1-syzkaller-07083-g4c9720875573 #0 Hardware name: IBM 3906 M04 701 (KVM/Linux) Call Trace: do_huge_pmd_anonymous_page+0xcda/0xd90 mm/huge_memory.c:744 create_huge_pmd mm/memory.c:4256 [inline] __handle_mm_fault+0xe6e/0x1068 mm/memory.c:4480 handle_mm_fault+0x288/0x748 mm/memory.c:4607 do_exception+0x394/0xae0 arch/s390/mm/fault.c:479 do_dat_exception+0x34/0x80 arch/s390/mm/fault.c:567 pgm_check_handler+0x1da/0x22c arch/s390/kernel/entry.S:706 copy_from_user_mvcos arch/s390/lib/uaccess.c:111 [inline] raw_copy_from_user+0x3a/0x88 arch/s390/lib/uaccess.c:174 _copy_from_user+0x48/0xa8 lib/usercopy.c:16 copy_from_user include/linux/uaccess.h:192 [inline] __do_sys_sigaltstack kernel/signal.c:4064 [inline] __s390x_sys_sigaltstack+0xc8/0x240 kernel/signal.c:4060 system_call+0xe0/0x28c arch/s390/kernel/entry.S:415 Allocated by task 9334: slab_alloc_node mm/slub.c:2891 [inline] slab_alloc mm/slub.c:2899 [inline] kmem_cache_alloc+0x118/0x348 mm/slub.c:2904 vm_area_dup+0x9c/0x2b8 kernel/fork.c:356 __split_vma+0xba/0x560 mm/mmap.c:2742 split_vma+0xca/0x108 mm/mmap.c:2800 mlock_fixup+0x4ae/0x600 mm/mlock.c:550 apply_vma_lock_flags+0x2c6/0x398 mm/mlock.c:619 do_mlock+0x1aa/0x718 mm/mlock.c:711 __do_sys_mlock2 mm/mlock.c:738 [inline] __s390x_sys_mlock2+0x86/0xa8 mm/mlock.c:728 system_call+0xe0/0x28c arch/s390/kernel/entry.S:415 Freed by task 9333: slab_free mm/slub.c:3142 [inline] kmem_cache_free+0x7c/0x4b8 mm/slub.c:3158 __vma_adjust+0x7b2/0x2508 mm/mmap.c:960 vma_merge+0x87e/0xce0 mm/mmap.c:1209 userfaultfd_release+0x412/0x6b8 fs/userfaultfd.c:868 __fput+0x22c/0x7a8 fs/file_table.c:281 task_work_run+0x200/0x320 kernel/task_work.c:151 tracehook_notify_resume include/linux/tracehook.h:188 [inline] do_notify_resume+0x100/0x148 arch/s390/kernel/signal.c:538 system_call+0xe6/0x28c arch/s390/kernel/entry.S:416 The buggy address belongs to the object at 00000000962d6948 which belongs to the cache vm_area_struct of size 200 The buggy address is located 64 bytes inside of 200-byte region [00000000962d6948, 00000000962d6a10) The buggy address belongs to the page: page:00000000313a09fe refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x962d6 flags: 0x3ffff00000000200(slab) raw: 3ffff00000000200 000040000257e080 0000000c0000000c 000000008020ba00 raw: 0000000000000000 000f001e00000000 ffffffff00000001 0000000096959501 page dumped because: kasan: bad access detected page->mem_cgroup:0000000096959501 Memory state around the buggy address: 00000000962d6880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000000962d6900: 00 fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb >00000000962d6980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ 00000000962d6a00: fb fb fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00000000962d6a80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ================================================================== Fixes: 6b251fc96cf2c ("userfaultfd: call handle_userfault() for userfaultfd_missing() faults") Reported-by: Alexander Egorenkov Signed-off-by: Gerald Schaefer Signed-off-by: Andrew Morton Cc: Andrea Arcangeli Cc: Heiko Carstens Cc: [4.3+] Link: https://lkml.kernel.org/r/20201110190329.11920-1-gerald.schaefer@linux.ibm.com Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -694,7 +694,6 @@ vm_fault_t do_huge_pmd_anonymous_page(st transparent_hugepage_use_zero_page()) { pgtable_t pgtable; struct page *zero_page; - bool set; vm_fault_t ret; pgtable = pte_alloc_one(vma->vm_mm, haddr); if (unlikely(!pgtable)) @@ -707,25 +706,25 @@ vm_fault_t do_huge_pmd_anonymous_page(st } vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); ret = 0; - set = false; if (pmd_none(*vmf->pmd)) { ret = check_stable_address_space(vma->vm_mm); if (ret) { spin_unlock(vmf->ptl); + pte_free(vma->vm_mm, pgtable); } else if (userfaultfd_missing(vma)) { spin_unlock(vmf->ptl); + pte_free(vma->vm_mm, pgtable); ret = handle_userfault(vmf, VM_UFFD_MISSING); VM_BUG_ON(ret & VM_FAULT_FALLBACK); } else { set_huge_zero_page(pgtable, vma->vm_mm, vma, haddr, vmf->pmd, zero_page); spin_unlock(vmf->ptl); - set = true; } - } else + } else { spin_unlock(vmf->ptl); - if (!set) pte_free(vma->vm_mm, pgtable); + } return ret; } gfp = alloc_hugepage_direct_gfpmask(vma);