From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752500AbdCELQU (ORCPT ); Sun, 5 Mar 2017 06:16:20 -0500 Received: from mail-vk0-f41.google.com ([209.85.213.41]:36409 "EHLO mail-vk0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752398AbdCELQS (ORCPT ); Sun, 5 Mar 2017 06:16:18 -0500 MIME-Version: 1.0 In-Reply-To: <20170304193910.GG29622@ZenIV.linux.org.uk> References: <20170304193910.GG29622@ZenIV.linux.org.uk> From: Dmitry Vyukov Date: Sun, 5 Mar 2017 12:15:56 +0100 Message-ID: Subject: Re: fs: use-after-free in path_lookupat To: Al Viro Cc: "linux-fsdevel@vger.kernel.org" , LKML , 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 On Sat, Mar 4, 2017 at 8:39 PM, Al Viro wrote: > On Sat, Mar 04, 2017 at 03:59:36PM +0100, Dmitry Vyukov wrote: > >> I am getting the following use-after-free reports while running >> syzkaller fuzzer on 86292b33d4b79ee03e2f43ea0381ef85f077c760 (but also >> happened on 6dc39c50e4aeb769c8ae06edf2b1a732f3490913 and >> c82be9d2244aacea9851c86f4fb74694c99cd874). > > IOW, it's not fs/namei.c patches from this window... > >> unlazy_walk+0xf2/0x4b0 fs/namei.c:692 > > Could you post disassembly (e.g. from objdump -d) of your unlazy_walk()? > For the kernel the trace is from... > >> 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? > > It doesn't, but is that the triggering call of name_to_handle_at(), or do you > have it called elsewhere? > > FWIW, no LOOKUP_ROOT in filename_lookup() flags + NULL root + dfd not > equal to AT_FDCWD + non-empty name should've ended up in > if (!d_can_lookup(dentry)) { > fdput(f); > return ERR_PTR(-ENOTDIR); > } > in path_init() and it shouldn't have progressed any further. And in case > of name_to_handle_at() we have user_path_at(dfd, name, lookup_flags, &path), > i.e. user_path_at_empty(dfd, name, lookup_flags, &path, NULL), i.e. > filename_lookup(dfd, getname_flags(name, lookup_flags, NULL), lookup_flags, > &path, NULL). IOW, filename_lookup() is called with root equal to NULL, > dfd and name coming straight from userland and lookup_flags containing > nothing beyond LOOKUP_EMPTY and LOOKUP_FOLLOW... I probably messed something. Here is a new report on 0710f3ff91ecc4a715db6e4d0690472b13c4dac6. Line numbers seem to match now. BUG: KASAN: use-after-free in debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline] at addr ffff880059c2ace4 BUG: KASAN: use-after-free in do_raw_spin_lock+0x1bb/0x1f0 kernel/locking/spinlock_debug.c:112 at addr ffff880059c2ace4 Read of size 4 by task syz-executor/21853 CPU: 0 PID: 21853 Comm: syz-executor Not tainted 4.10.0+ #293 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x2fb/0x3fd lib/dump_stack.c:52 kasan_object_err+0x1c/0x90 mm/kasan/report.c:166 print_address_description mm/kasan/report.c:208 [inline] kasan_report_error mm/kasan/report.c:292 [inline] kasan_report.part.2+0x1b0/0x460 mm/kasan/report.c:314 kasan_report mm/kasan/report.c:334 [inline] __asan_report_load4_noabort+0x29/0x30 mm/kasan/report.c:334 debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline] do_raw_spin_lock+0x1bb/0x1f0 kernel/locking/spinlock_debug.c:112 __raw_spin_lock include/linux/spinlock_api_smp.h:143 [inline] _raw_spin_lock+0x3b/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:00007f462e243b58 EFLAGS: 00000286 ORIG_RAX: 000000000000012f RAX: ffffffffffffffda RBX: 0000000000000051 RCX: 00000000004458d9 RDX: 0000000020002ff3 RSI: 0000000020002ffa RDI: 0000000000000051 RBP: 00000000006e11b0 R08: 0000000000001000 R09: 0000000000000000 R10: 0000000020002000 R11: 0000000000000286 R12: 0000000000708000 R13: 0000000020000000 R14: 0000000000013000 R15: 0000000000000003 Object at ffff880059c2ac60, in cache dentry size: 288 Allocated: PID = 21878 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack+0x43/0xd0 mm/kasan/kasan.c:513 set_track mm/kasan/kasan.c:525 [inline] kasan_kmalloc+0xaa/0xd0 mm/kasan/kasan.c:616 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:555 kmem_cache_alloc+0x102/0x6e0 mm/slab.c:3572 __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:4157 shmem_file_setup mm/shmem.c:4212 [inline] SYSC_memfd_create mm/shmem.c:3672 [inline] SyS_memfd_create+0x172/0x2c0 mm/shmem.c:3630 entry_SYSCALL_64_fastpath+0x1f/0xc2 Freed: PID = 21878 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack+0x43/0xd0 mm/kasan/kasan.c:513 set_track mm/kasan/kasan.c:525 [inline] kasan_slab_free+0x6f/0xb0 mm/kasan/kasan.c:589 __cache_free mm/slab.c:3514 [inline] kmem_cache_free+0x71/0x240 mm/slab.c:3774 __d_free fs/dcache.c:265 [inline] dentry_free+0xd5/0x160 fs/dcache.c:314 __dentry_kill+0x471/0x6d0 fs/dcache.c:552 dentry_kill fs/dcache.c:579 [inline] dput.part.25+0x5ce/0x7c0 fs/dcache.c:791 dput+0x1f/0x30 fs/dcache.c:753 __fput+0x538/0x800 fs/file_table.c:227 ____fput+0x15/0x20 fs/file_table.c:245 task_work_run+0x197/0x260 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:161 prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline] syscall_return_slowpath+0x4d3/0x570 arch/x86/entry/common.c:260 entry_SYSCALL_64_fastpath+0xc0/0xc2 Memory state around the buggy address: ffff880059c2ab80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff880059c2ac00: 00 00 00 00 fc fc fc fc fc fc fc fc fb fb fb fb >ffff880059c2ac80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff880059c2ad00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff880059c2ad80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00 ==================================================================