Re: io_uring NULL pointer dereference on Linux v5.4-rc1

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, Oct 09, 2019 at 05:27:44AM -0600, Jens Axboe wrote:
> On 10/9/19 3:23 AM, Stefan Hajnoczi wrote:
> > I hit this NULL pointer dereference when running qemu-iotests 052 (raw)
> > on both ext4 and XFS on dm-thin/luks.  The kernel is Linux v5.4-rc1 but
> > I haven't found any obvious fixes in Jens' tree, so it's likely that
> > this bug is still present:
> > 
> > BUG: kernel NULL pointer dereference, address: 0000000000000102
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not-present page
> > PGD 0 P4D 0
> > Oops: 0000 [#1] SMP PTI
> > CPU: 2 PID: 6656 Comm: qemu-io Not tainted 5.4.0-rc1 #1
> > Hardware name: LENOVO 20BTS1N70V/20BTS1N70V, BIOS N14ET37W (1.15 ) 09/06/2016
> > RIP: 0010:__queue_work+0x1f/0x3b0
> > Code: eb df 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 57 49 89 f7 41 56 41 89 fe 41 55 41 89 fd 41 54 55 48 89 d5 53 48 83 ec 10 <f6> 86 02 01 00 00 01 0f 85 bc 02 00 00 49 bc eb 83 b5 80 46 86 c8
> > RSP: 0018:ffffbef4884bbd58 EFLAGS: 00010082
> > RAX: 0000000000000246 RBX: 0000000000000246 RCX: 0000000000000000
> > RDX: ffff9903901f4460 RSI: 0000000000000000 RDI: 0000000000000040
> > RBP: ffff9903901f4460 R08: ffff9903901fb040 R09: ffff990398614700
> > R10: 0000000000000030 R11: 0000000000000000 R12: 0000000000000000
> > R13: 0000000000000040 R14: 0000000000000040 R15: 0000000000000000
> > FS:  00007f7d2a4e4a80(0000) GS:ffff9903a5a80000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000000102 CR3: 0000000203da8004 CR4: 00000000003606e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >   ? __io_queue_sqe+0xa1/0x200
> >   queue_work_on+0x36/0x40
> >   __io_queue_sqe+0x16e/0x200
> >   io_ring_submit+0xd2/0x230
> >   ? percpu_ref_resurrect+0x46/0x70
> >   ? __io_uring_register+0x207/0xa30
> >   ? __schedule+0x286/0x700
> >   __x64_sys_io_uring_enter+0x1a3/0x280
> >   ? __x64_sys_io_uring_register+0x64/0xb0
> >   do_syscall_64+0x5b/0x180
> >   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > RIP: 0033:0x7f7d3439f1fd
> > Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 5b 8c 0c 00 f7 d8 64 89 01 48
> > RSP: 002b:00007f7d2918d408 EFLAGS: 00000216 ORIG_RAX: 00000000000001aa
> > RAX: ffffffffffffffda RBX: 00007f7d2918d4f0 RCX: 00007f7d3439f1fd
> > RDX: 0000000000000000 RSI: 0000000000000001 RDI: 000000000000000a
> > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000008
> > R10: 0000000000000000 R11: 0000000000000216 R12: 00005616e3c32ab8
> > R13: 00005616e3c32b78 R14: 00005616e3c32ab0 R15: 0000000000000001
> > Modules linked in: fuse ccm xt_CHECKSUM xt_MASQUERADE tun bridge stp llc nf_conntrack_netbios_ns nf_conntrack_broadcast xt_CT ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat iptable_mangle iptable_raw iptable_security nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables sunrpc vfat fat intel_rapl_msr rmi_smbus iwlmvm rmi_core intel_rapl_common x86_pkg_temp_thermal intel_powerclamp coretemp mac80211 snd_hda_codec_realtek snd_hda_codec_generic snd_hda_codec_hdmi kvm_intel snd_hda_intel kvm snd_intel_nhlt snd_hda_codec snd_usb_audio irqbypass uvcvideo snd_hda_core snd_usbmidi_lib snd_rawmidi iTCO_wdt snd_hwdep libarc4 intel_cstate cdc_ether intel_uncore videobuf2_vmalloc iwlwifi mei_wdt mei_hdcp iTCO_vendor_support snd_seq videobuf2_memops usbnet videobuf2_v4l2 snd_seq_device
> >   intel_rapl_perf pcspkr videobuf2_common joydev wmi_bmof snd_pcm cfg80211 r8152 videodev intel_pch_thermal i2c_i801 mii mc thinkpad_acpi snd_timer mei_me ledtrig_audio snd lpc_ich mei soundcore rfkill binfmt_misc xfs dm_thin_pool dm_persistent_data dm_bio_prison libcrc32c dm_crypt i915 i2c_algo_bit drm_kms_helper drm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel serio_raw wmi video
> > CR2: 0000000000000102
> > ---[ end trace 2ac747acabe218da ]---
> > RIP: 0010:__queue_work+0x1f/0x3b0
> > Code: eb df 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 57 49 89 f7 41 56 41 89 fe 41 55 41 89 fd 41 54 55 48 89 d5 53 48 83 ec 10 <f6> 86 02 01 00 00 01 0f 85 bc 02 00 00 49 bc eb 83 b5 80 46 86 c8
> > RSP: 0018:ffffbef4884bbd58 EFLAGS: 00010082
> > RAX: 0000000000000246 RBX: 0000000000000246 RCX: 0000000000000000
> > RDX: ffff9903901f4460 RSI: 0000000000000000 RDI: 0000000000000040
> > RBP: ffff9903901f4460 R08: ffff9903901fb040 R09: ffff990398614700
> > R10: 0000000000000030 R11: 0000000000000000 R12: 0000000000000000
> > R13: 0000000000000040 R14: 0000000000000040 R15: 0000000000000000
> > FS:  00007f7d2a4e4a80(0000) GS:ffff9903a5a80000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000000102 CR3: 0000000203da8004 CR4: 00000000003606e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > 
> > Unfortunately I don't have time to find the root cause.  What I've
> > figured out so far is:
> > 
> >    bool queue_work_on(int cpu, struct workqueue_struct *wq,
> >                       struct work_struct *work)
> >    {
> >        bool ret = false;
> >        unsigned long flags;
> > 
> >        local_irq_save(flags);
> > 
> >        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
> >                                                       ~~~~~~~~~~~~~~~~~~~~
> > 
> > The address of work is 0x102 so this line causes a page fault when it
> > tries to access the data field (offset 0).
> > 
> > The caller provided the 0x102 pointer so let's see where it comes from:
> > 
> >    static int __io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
> >                              struct sqe_submit *s, bool force_nonblock)
> >    {
> >        ...
> >        if (!io_add_to_prev_work(list, req)) {
> >            if (list)
> >                atomic_inc(&list->cnt);
> >            INIT_WORK(&req->work, io_sq_wq_submit_work);
> >            io_queue_async_work(ctx, req);
> > 	  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > and queue_work() is called here:
> > 
> >    static inline void io_queue_async_work(struct io_ring_ctx *ctx,
> >                                           struct io_kiocb *req)
> >    {
> >        int rw = 0;
> > 
> >        if (req->submit.sqe) {
> >            switch (req->submit.sqe->opcode) {
> >            case IORING_OP_WRITEV:
> >            case IORING_OP_WRITE_FIXED:
> >                rw = !(req->rw.ki_flags & IOCB_DIRECT);
> >                break;
> >            }
> >        }
> > 
> >        queue_work(ctx->sqo_wq[rw], &req->work);
> >        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > I must be missing something though because it seems impossible to get
> > this far if req is NULL.  INIT_WORK() would have Oopsed already.  Also,
> > offsetof(struct io_kiocb, work) is 0xa0 according to pahole(1) so we
> > still haven't reached the 0x102 offset from the Oops report.
> > 
> > Any ideas?
> 
> This is new in 5.4-rc1?

I didn't hit it with 5.3, but I hit other issues so I'm not sure if this
bug exists in older kernels.

> And how are you reproducing it?

  $ git clone -b io_uring https://github.com/stefanha/qemu
  $ cd qemu
  $ ./configure --target-list=x86_64-softmmu
  $ make -j$(nproc)
  $ (cd tests/qemu-iotests && ./check -i io_uring 052)

You can mount the file system of your choice at
tests/qemu-iotests/scratch/ before running the test.

You can view the test case at tests/qemu-iotests/052.

Stefan

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