From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752145AbdCDPAA (ORCPT ); Sat, 4 Mar 2017 10:00:00 -0500 Received: from mail-vk0-f50.google.com ([209.85.213.50]:35295 "EHLO mail-vk0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751814AbdCDO76 (ORCPT ); Sat, 4 Mar 2017 09:59:58 -0500 MIME-Version: 1.0 From: Dmitry Vyukov Date: Sat, 4 Mar 2017 15:59:36 +0100 Message-ID: Subject: fs: use-after-free in path_lookupat To: Al Viro , "linux-fsdevel@vger.kernel.org" , LKML Cc: syzkaller Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, I am getting the following use-after-free reports while running syzkaller fuzzer on 86292b33d4b79ee03e2f43ea0381ef85f077c760 (but also happened on 6dc39c50e4aeb769c8ae06edf2b1a732f3490913 and c82be9d2244aacea9851c86f4fb74694c99cd874). ================================================================== BUG: KASAN: use-after-free in perf_trace_lock_acquire+0x9cf/0xa00 include/trace/events/lock.h:12 at addr ffff88008477c930 Read of size 8 by task syz-executor3/878 CPU: 1 PID: 878 Comm: syz-executor3 Not tainted 4.10.0+ #276 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __asan_report_load8_noabort+0x29/0x30 mm/kasan/report.c:331 perf_trace_lock_acquire+0x9cf/0xa00 include/trace/events/lock.h:12 trace_lock_acquire include/trace/events/lock.h:12 [inline] lock_acquire+0x473/0x630 kernel/locking/lockdep.c:3752 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline] _raw_spin_lock+0x33/0x50 kernel/locking/spinlock.c:151 spin_lock include/linux/spinlock.h:299 [inline] lockref_get_not_dead+0x19/0x80 lib/lockref.c:179 legitimize_path.isra.36+0x7d/0x1a0 fs/namei.c:640 unlazy_walk+0xf2/0x4b0 fs/namei.c:692 complete_walk+0xb2/0x1f0 fs/namei.c:805 path_lookupat+0x1c1/0x400 fs/namei.c:2275 filename_lookup+0x282/0x540 fs/namei.c:2301 user_path_at_empty+0x40/0x50 fs/namei.c:2555 user_path_at include/linux/namei.h:55 [inline] SYSC_name_to_handle_at fs/fhandle.c:106 [inline] SyS_name_to_handle_at+0xff/0x720 fs/fhandle.c:92 entry_SYSCALL_64_fastpath+0x1f/0xc2 RIP: 0033:0x4458d9 RSP: 002b:00007f2162048b58 EFLAGS: 00000286 ORIG_RAX: 000000000000012f RAX: ffffffffffffffda RBX: 0000000000000053 RCX: 00000000004458d9 RDX: 0000000020002ff3 RSI: 0000000020002ffa RDI: 0000000000000053 RBP: 00000000006e11b0 R08: 0000000000001000 R09: 0000000000000000 R10: 0000000020002000 R11: 0000000000000286 R12: 0000000000708000 R13: 0000000000000005 R14: 0000000000708020 R15: 00007f2162049700 Object at ffff88008477c880, in cache dentry size: 288 Allocated: PID = 878 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:544 kmem_cache_alloc+0x102/0x6e0 mm/slab.c:3571 __d_alloc+0xb3/0xbb0 fs/dcache.c:1571 d_alloc_pseudo+0x1d/0x30 fs/dcache.c:1692 __shmem_file_setup+0x20c/0x5a0 mm/shmem.c:4156 shmem_file_setup mm/shmem.c:4211 [inline] SYSC_memfd_create mm/shmem.c:3671 [inline] SyS_memfd_create+0x172/0x2c0 mm/shmem.c:3629 entry_SYSCALL_64_fastpath+0x1f/0xc2 Freed: PID = 887 kmem_cache_free+0x71/0x240 mm/slab.c:3773 __d_free fs/dcache.c:265 [inline] dentry_free+0xd5/0x150 fs/dcache.c:314 __dentry_kill+0x471/0x6d0 fs/dcache.c:552 dentry_kill fs/dcache.c:579 [inline] dput.part.26+0x5ce/0x7c0 fs/dcache.c:791 dput+0x1f/0x30 fs/dcache.c:753 __fput+0x527/0x7f0 fs/file_table.c:226 ____fput+0x15/0x20 fs/file_table.c:244 task_work_run+0x18a/0x260 kernel/task_work.c:116 tracehook_notify_resume include/linux/tracehook.h:191 [inline] exit_to_usermode_loop+0x23b/0x2a0 arch/x86/entry/common.c:160 prepare_exit_to_usermode arch/x86/entry/common.c:190 [inline] syscall_return_slowpath+0x4d3/0x570 arch/x86/entry/common.c:259 entry_SYSCALL_64_fastpath+0xc0/0xc2 Memory state around the buggy address: ffff88008477c800: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc ffff88008477c880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff88008477c900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88008477c980: fb fb fb fb fc fc fc fc fc fc fc fc fb fb fb fb ffff88008477ca00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== Here are 3 more, but they look essentially the same: https://gist.githubusercontent.com/dvyukov/9c50026c9a82f46cfedf871a48b14b63/raw/9a5d03f10e6eeac3e2113a808463796f9e2921a3/gistfile1.txt This is barely reproducible on large syzkaller programs. Here are 3 of them. They look very close, so they are probably mutations of the same program: https://gist.githubusercontent.com/dvyukov/f0e9ce7798c6003b8bae4ddb925f10f6/raw/faddf1609c0bfe8cf0465e62204050a95a98323f/gistfile1.txt Running these programs as: ./syz-execprog -repeat=0 -procs=24 -sandbox=namespace prog reproduces the crash sometimes after a minute, sometimes after half an hour. Because of that I can't minimize the reproducer. However, from the crashes it's clear that involved syscalls are memfd_create and name_to_handle_at and all programs contain: r4 = memfd_create(&(0x7f0000013000)="2f6465762f6877726e6700", 0x0) name_to_handle_at(r4, &(0x7f0000003000-0x6)="2e2f62757300", &(0x7f0000003000-0xd)={0xc, 0x0, "cd21"}, &(0x7f0000002000)=0x0, 0x1000) What's strange is that dirfd passed to name_to_handle_at is memfd handle (sic). And path lookup somehow does not fail early on this. Does it make any sense? But I don't know if the crash is specific to these calls, or maybe it's just a common race in lookup code that happens to happen on this program. Any ideas how such crash can happen?