Re: [PATCH] hyper-v: Check for ring buffer in hv_get_bytes_to_read/write

[Mohammed Gamal <mgamal@redhat.com>]

On Wed, 2019-03-13 at 21:12 +0000, Stephen Hemminger wrote:
> What test are you running?

I am running iperf3 with the following arguments:
iperf3 -u -c ${iperf3 server address} -b 0 -P8 -t 3600

while changing the interface parameters in parallel with the following
script:

cat ./test.sh
#!/bin/bash
device="eth1"
i=0
while [ "$i" -lt 1000 ]
do
    ethtool -L $device combined 1
    ethtool -L $device combined 2
    let "i++"
    echo $i
done

> 
> -----Original Message-----
> From: Mohammed Gamal <mgamal@redhat.com> 
> Sent: Wednesday, March 13, 2019 3:25 AM
> To: Haiyang Zhang <haiyangz@microsoft.com>; Michael Kelley <mikelley@
> microsoft.com>; linux-hyperv@vger.kernel.org; kimbrownkd <kimbrownkd@
> gmail.com>
> Cc: Sasha Levin <Alexander.Levin@microsoft.com>; Dexuan Cui <decui@mi
> crosoft.com>; Stephen Hemminger <sthemmin@microsoft.com>; Long Li <lo
> ngli@microsoft.com>; KY Srinivasan <kys@microsoft.com>; vkuznets <vku
> znets@redhat.com>; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH] hyper-v: Check for ring buffer in
> hv_get_bytes_to_read/write
> 
> On Tue, 2019-03-12 at 18:02 +0000, Haiyang Zhang wrote:
> >  
> >  
> > > -----Original Message-----
> > > From: Mohammed Gamal <mgamal@redhat.com>
> > > Sent: Thursday, March 7, 2019 1:32 PM
> > > To: Michael Kelley <mikelley@microsoft.com>; linux-hyperv@vger.ke
> > > rn
> > 
> > el.org;
> > > kimbrownkd <kimbrownkd@gmail.com>
> > > Cc: Sasha Levin <Alexander.Levin@microsoft.com>; Dexuan Cui
> > > <decui@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>
> > > ;
> > > Long Li <longli@microsoft.com>; KY Srinivasan <kys@microsoft.com>
> > > ;
> > 
> > Haiyang
> > > Zhang <haiyangz@microsoft.com>; vkuznets <vkuznets@redhat.com>;
> > 
> > linux-
> > > kernel@vger.kernel.org
> > > Subject: Re: [PATCH] hyper-v: Check for ring buffer in
> > > hv_get_bytes_to_read/write
> > > 
> > > On Thu, 2019-03-07 at 17:33 +0000, Michael Kelley wrote:
> > > > From: Mohammed Gamal <mgamal@redhat.com> Sent: Thursday, March
> > > > 7,
> > > > 2019 8:36 AM
> > > > > 
> > > > > This patch adds a check for the presence of the ring buffer
> > > > > in
> > > > > hv_get_bytes_to_read/write() to avoid possible NULL pointer
> > > > > dereferences.
> > > > > If the ring buffer is not yet allocated, return 0 bytes to be
> > > > > read/written.
> > > > > 
> > > > > The root cause is that code that accesses the ring buffer
> > 
> > including
> > > > > hv_get_bytes_to_read/write() could be vulnerable to the race
> > > > > condition discussed in
> > > > > https://nam06.safelinks.protection.outlook.com/?url=https%3A%
> > > > > 2F
> > 
> > %2Flk
> > > > > 
> > > 
> > > ml.org%2Flkml%2F2018%2F10%2F18%2F779&amp;data=02%7C01%7Chaiyangz
> > > %40m
> > > > > 
> > > 
> > > icrosoft.com%7C73af013c14034bb0b1ad08d6a32b419c%7C72f988bf86f141a
> > > f9
> > > 1
> > > > > 
> > > 
> > > ab2d7cd011db47%7C1%7C0%7C636875803518430021&amp;sdata=b51Xc5GUN
> > > nHX0K
> > > > > 08LrH3ShTyFcRZ4mYHUATd%2BDpvYDw%3D&amp;reserved=0>;
> > > > > 
> > > > > This race is being addressed by the patch series by Kimberly
> > 
> > Brown
> > > > > in
> > > > > https://nam06.safelinks.protection.outlook.com/?url=https%3A%
> > > > > 2F
> > 
> > %2Flk
> > > > > 
> > > 
> > > ml.org%2Flkml%2F2019%2F2%2F21%2F1236&amp;data=02%7C01%7Chaiyangz
> > > %40m
> > > > > 
> > > 
> > > icrosoft.com%7C73af013c14034bb0b1ad08d6a32b419c%7C72f988bf86f141a
> > > f9
> > > 1
> > > > > 
> > > 
> > > ab2d7cd011db47%7C1%7C0%7C636875803518430021&amp;sdata=js1ff15Gbk7
> > > 0MD
> > > > > A2hkMZExxvAAbDuKDhfBvc5ZrckzM%3D&amp;reserved=0 which is not
> > > 
> > > final
> > > > > yet
> > > > > 
> > > > > Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> > > > 
> > > > Could you elaborate on the code paths where
> > > > hv_get_bytes_to_read/write() could be called when the ring
> > > > buffer
> > > > isn't yet allocated?  My sense is that Kim Brown's patch will
> > 
> > address
> > > > all of the code paths that involved sysfs access from outside
> > > > the
> > > > driver.  And within a driver, the ring buffer should never be
> > 
> > accessed
> > > > unless it is already allocated.  Is there another code path
> > > > we're
> > 
> > not
> > > > aware of?  I'm wondering if these changes are really needed
> > > > once
> > 
> > Kim
> > > > Brown's patch is finished.
> > > > 
> > > > Michael
> > > 
> > > I've seen one instance of the race in the netvsc driver when
> > 
> > running traffic
> > > through it with iperf3 while continuously changing the channel
> > 
> > settings.
> > > 
> > > The following code path deallocates the ring buffer:
> > > netvsc_set_channels() -> netvsc_detach() ->
> > > rndis_filter_device_remove() -> netvsc_device_remove() ->
> > 
> > vmbus_close()
> > > -> vmbus_free_ring() -> hv_ringbuffer_cleanup().
> > > 
> > > netvsc_send_pkt() -> hv_get_bytes_to_write() might get called
> > 
> > concurrently
> > > after vmbus_close() and before vmbus_open() returns and sets up
> > > the
> > 
> > new ring
> > > buffer.
> > > 
> > > The race is fairly hard to reproduce on recent upstream kernels,
> > 
> > but I still
> > > managed to reproduce it.
> > 
> >  
> > Looking at the code from netvsc_detach() –
> >          netif_tx_disable(ndev) is called before
> > rndis_filter_device_remove(hdev, nvdev).
> > So there should be no call to netvsc_send_pkt() after detaching.
> > What’s the crash stack trace?
> >  
> > static int netvsc_detach(struct net_device *ndev,
> >                          struct netvsc_device *nvdev)
> > {
> >         struct net_device_context *ndev_ctx = netdev_priv(ndev);
> >         struct hv_device *hdev = ndev_ctx->device_ctx;
> >         int ret;
> >  
> >         /* Don't try continuing to try and setup sub channels */
> >         if (cancel_work_sync(&nvdev->subchan_work))
> >                 nvdev->num_chn = 1;
> >  
> >         /* If device was up (receiving) then shutdown */
> >         if (netif_running(ndev)) {
> >                 netif_tx_disable(ndev);
> >  
> >                 ret = rndis_filter_close(nvdev);
> >                 if (ret) {
> >                         netdev_err(ndev,
> >                                    "unable to close device (ret
> > %d).\n", ret);
> >                         return ret;
> >                 }
> >  
> >                 ret = netvsc_wait_until_empty(nvdev);
> >                 if (ret) {
> >                         netdev_err(ndev,
> >                                    "Ring buffer not empty after
> > closing rndis\n");
> >                         return ret;
> >                 }
> >         }
> >  
> >         netif_device_detach(ndev);
> >  
> >         rndis_filter_device_remove(hdev, nvdev);
> >  
> >         return 0;
> > }
> >  
> > Thanks,
> > Haiyang
> 
> Here is one stack trace on a 4.18 kernel, the most recent kernel I
> managed to reproduce this bug on. 
> I haven't managed to reproduce on 5.0.0 yet, but I guess some recent
> changes to the netvsc driver could be masking the problem, as I tried
> backporting those changes to older RHEL 7 kernels and still managed
> to
> reproduce the problem there. I could however be wrong, and any
> pointers
> are still appreciated:
> 
> [  545.308507] BUG: unable to handle kernel NULL pointer dereference
> at
> 0000000000000004
> [  545.308656] PGD 0 P4D 0 
> [  545.308763] Oops: 0000 [#1] SMP PTI
> [  545.308855] CPU: 2 PID: 1800 Comm: iperf3 Kdump: loaded Not
> tainted
> 4.18.0-64.el8.test.x86_64 #1
> [  545.308990] Hardware name: Microsoft Corporation Virtual
> Machine/Virtual Machine, BIOS Hyper-V UEFI Release v1.0 11/26/2012
> [  545.309143] RIP: 0010:netvsc_send+0x2c9/0xce0 [hv_netvsc]
> [  545.309298] Code: 4c 8b b1 c0 00 00 00 4f 8d 2c 64 49 c1 e5 07 4d
> 03
> ae c0 03 00 00 48 8b 84 03 30 01 00 00 4c 89 6c 24 18 48 8b 90 20 01
> 00
> 00 <8b> 72 04 8b 0a 8b 90 38 01 00 00 89 f7 01 f2 29 cf 29 ca 39 ce
>  0f
> [  545.309321] RSP: 0018:ffffb8a305d5b6c0 EFLAGS: 00010282
> [  545.309321] RAX: ffff926928bd7000 RBX: ffff92687dbe0000 RCX:
> ffff92687d5bec00
> [  545.309321] RDX: 0000000000000000 RSI: ffff92691b61c654 RDI:
> 0000000000000000
> [  545.309321] RBP: ffff926915dcde28 R08: ffff926915dcde00 R09:
> 0000000000000000
> [  545.309321] R10: 00000000000db61c R11: 0000000000000f7e R12:
> 0000000000000001
> [  545.309321] R13: ffff926931808180 R14: ffff926931801000 R15:
> 0000000000000000
> [  545.309321] FS:  00007feca6a4b740(0000) GS:ffff926940080000(0000)
> knlGS:0000000000000000
> [  545.309321] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  545.309321] CR2: 0000000000000004 CR3: 00000000dfccc004 CR4:
> 00000000003606e0
> [  545.309321] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [  545.309321] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [  545.309321] Call Trace:
> [  545.309321]  netvsc_start_xmit+0x3c9/0x800 [hv_netvsc]
> [  545.309321]  ? __switch_to_asm+0x34/0x70
> [  545.309321]  ? __switch_to_asm+0x34/0x70
> [  545.309321]  ? ___slab_alloc+0x269/0x4e0
> [  545.309321]  ? __alloc_skb+0x82/0x1c0
> [  545.309321]  ? nft_do_chain+0x3d7/0x3f0 [nf_tables]
> [  545.309321]  ? nft_do_chain+0x3d7/0x3f0 [nf_tables]
> [  545.309321]  ? nft_do_chain+0x3d7/0x3f0 [nf_tables]
> [  545.309321]  ? _cond_resched+0x15/0x30
> [  545.309321]  ? netif_skb_features+0x118/0x280
> [  545.309321]  dev_hard_start_xmit+0xa5/0x210
> [  545.309321]  sch_direct_xmit+0x14f/0x340
> [  545.309321]  __dev_queue_xmit+0x799/0x8f0
> [  545.309321]  ip_finish_output2+0x2e0/0x430
> [  545.309321]  ? ip_finish_output+0x139/0x270
> [  545.309321]  ip_output+0x6c/0xe0
> [  545.309321]  ? ip_append_data.part.50+0xc0/0xc0
> [  545.309321]  ip_send_skb+0x15/0x40
> [  545.309321]  udp_send_skb.isra.43+0x153/0x340
> [  545.309321]  udp_sendmsg+0xac2/0xd30
> [  545.309321]  ? set_fd_set.part.7+0x40/0x40
> [  545.309321]  ? set_fd_set.part.7+0x40/0x40
> [  545.309321]  ? __check_object_size+0xa3/0x181
> [  545.309321]  ? sock_has_perm+0x78/0xa0
> [  545.309321]  ? core_sys_select+0x242/0x2f0
> [  545.309321]  ? sock_sendmsg+0x36/0x40
> [  545.309321]  ? udp_push_pending_frames+0x60/0x60
> [  545.309321]  sock_sendmsg+0x36/0x40
> [  545.309321]  sock_write_iter+0x8f/0xf0
> [  545.309321]  __vfs_write+0x156/0x1a0
> [  545.309321]  vfs_write+0xa5/0x1a0
> [  545.309321]  ksys_write+0x4f/0xb0
> [  545.309321]  do_syscall_64+0x5b/0x1b0
> [  545.309321]  entry_SYSCALL_64_after_hwframe+0x65/0xca
> [  545.309321] RIP: 0033:0x7feca5fb5348
> [  545.309321] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00
> 00
> 00 f3 0f 1e fa 48 8d 05 d5 63 2d 00 8b 00 85 c0 75 17 b8 01 00 00 00
> 0f
> 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4
> 55
> [  545.309321] RSP: 002b:00007ffc3ff1f108 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000001
> [  545.309321] RAX: ffffffffffffffda RBX: 00000000000005a8 RCX:
> 00007feca5fb5348
> [  545.309321] RDX: 00000000000005a8 RSI: 00007feca6a59000 RDI:
> 0000000000000009
> [  545.309321] RBP: 00007feca6a59000 R08: 0000000000000002 R09:
> 00cd09a3238b4e43
> [  545.309321] R10: 0002961ecea49016 R11: 0000000000000246 R12:
> 0000000000000009
> [  545.309321] R13: 00000000000005a8 R14: 00007ffc3ff1f180 R15:
> 0000563c1e05b260
> [  545.309321] Modules linked in: nft_chain_nat_ipv6
> nf_conntrack_ipv6
> nf_defrag_ipv6 nf_nat_ipv6 nft_chain_route_ipv6 nft_chain_nat_ipv4
> nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat
> nft_chain_route_ipv4 nf_conntrack ip_set nf_tables nfnetlink vfat fat
> sb_edac crct10dif_pclmul crc32_pclmul ghash_clmulni_intel
> intel_rapl_perf sg hv_utils hv_balloon pcspkr joydev xfs libcrc32c
> sd_mod sr_mod cdrom serio_raw hv_storvsc hv_netvsc scsi_transport_fc
> hyperv_fb hyperv_keyboard hid_hyperv crc32c_intel hv_vmbus dm_mirror
> dm_region_hash dm_log dm_mod [last unloaded: nft_compat]
> [  545.309321] CR2: 0000000000000004
> 
> From the stack trace netvsc_send+0x2c9 points to this line:
> 
> static inline u32 hv_get_bytes_to_write(const struct 	hv_ring_
> bu
> ffer_info *rbi)
> {
>         u32 read_loc, write_loc, dsize, write;
> 
>         dsize = rbi->ring_datasize;
>         read_loc = READ_ONCE(rbi->ring_buffer->read_index);  <-------
> --
>         write_loc = rbi->ring_buffer->write_index;
> 
>         write = write_loc >= read_loc ? dsize - (write_loc -
> read_loc) 
>                 read_loc - write_loc;
>         return write;
> }
> 
> which gets called from netvsc_send_pkt().