On Tue, 2019-03-12 at 18:02 +0000, Haiyang Zhang wrote:
>
>
> > -----Original Message-----
> > From: Mohammed Gamal <mga...@redhat.com>
> > Sent: Thursday, March 7, 2019 1:32 PM
> > To: Michael Kelley <mikel...@microsoft.com>; linux-hyp...@vger.kern
> el.org;
> > kimbrownkd <kimbrow...@gmail.com>
> > Cc: Sasha Levin <alexander.le...@microsoft.com>; Dexuan Cui
> > <de...@microsoft.com>; Stephen Hemminger <sthem...@microsoft.com>;
> > Long Li <lon...@microsoft.com>; KY Srinivasan <k...@microsoft.com>;
> Haiyang
> > Zhang <haiya...@microsoft.com>; vkuznets <vkuzn...@redhat.com>;
> linux-
> > ker...@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 <mga...@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&data=02%7C01%7Chaiyangz
> > %40m
> > > >
> > icrosoft.com%7C73af013c14034bb0b1ad08d6a32b419c%7C72f988bf86f141af9
> > 1
> > > >
> > ab2d7cd011db47%7C1%7C0%7C636875803518430021&sdata=b51Xc5GUN
> > nHX0K
> > > > 08LrH3ShTyFcRZ4mYHUATd%2BDpvYDw%3D&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&data=02%7C01%7Chaiyangz
> > %40m
> > > >
> > icrosoft.com%7C73af013c14034bb0b1ad08d6a32b419c%7C72f988bf86f141af9
> > 1
> > > >
> > ab2d7cd011db47%7C1%7C0%7C636875803518430021&sdata=js1ff15Gbk7
> > 0MD
> > > > A2hkMZExxvAAbDuKDhfBvc5ZrckzM%3D&reserved=0 which is not
> > final
> > > > yet
> > > >
> > > > Signed-off-by: Mohammed Gamal <mga...@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().
