netdev - Re: [PATCH net-next] bonding/main: fix NULL dereference in bond_select_active

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Date:   Mon, 1 Jul 2019 21:31:57 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        John Sperbeck <jsperbeck@...gle.com>,
        Jarod Wilson <jarod@...hat.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH net-next] bonding/main: fix NULL dereference in bond_select_active_slave()

On Mon, Jul 1, 2019 at 9:15 PM Jay Vosburgh <jay.vosburgh@...onical.com> wrote:
>
> Eric Dumazet <edumazet@...gle.com> wrote:
>
> >A bonding master can be up while best_slave is NULL.
> >
> >[12105.636318] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
> >[12105.638204] mlx4_en: eth1: Linkstate event 1 -> 1
> >[12105.648984] IP: bond_select_active_slave+0x125/0x250
> >[12105.653977] PGD 0 P4D 0
> >[12105.656572] Oops: 0000 [#1] SMP PTI
> >[12105.660487] gsmi: Log Shutdown Reason 0x03
> >[12105.664620] Modules linked in: kvm_intel loop act_mirred uhaul vfat fat stg_standard_ftl stg_megablocks stg_idt stg_hdi stg elephant_dev_num stg_idt_eeprom w1_therm wire i2c_mux_pca954x i2c_mux mlx4_i2c i2c_usb cdc_acm ehci_pci ehci_hcd i2c_iimc mlx4_en mlx4_ib ib_uverbs ib_core mlx4_core [last unloaded: kvm_intel]
> >[12105.685686] mlx4_core 0000:03:00.0: dispatching link up event for port 2
> >[12105.685700] mlx4_en: eth2: Linkstate event 2 -> 1
> >[12105.685700] mlx4_en: eth2: Link Up (linkstate)
> >[12105.724452] Workqueue: bond0 bond_mii_monitor
> >[12105.728854] RIP: 0010:bond_select_active_slave+0x125/0x250
> >[12105.734355] RSP: 0018:ffffaf146a81fd88 EFLAGS: 00010246
> >[12105.739637] RAX: 0000000000000003 RBX: ffff8c62b03c6900 RCX: 0000000000000000
> >[12105.746838] RDX: 0000000000000000 RSI: ffffaf146a81fd08 RDI: ffff8c62b03c6000
> >[12105.754054] RBP: ffffaf146a81fdb8 R08: 0000000000000001 R09: ffff8c517d387600
> >[12105.761299] R10: 00000000001075d9 R11: ffffffffaceba92f R12: 0000000000000000
> >[12105.768553] R13: ffff8c8240ae4800 R14: 0000000000000000 R15: 0000000000000000
> >[12105.775748] FS:  0000000000000000(0000) GS:ffff8c62bfa40000(0000) knlGS:0000000000000000
> >[12105.783892] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >[12105.789716] CR2: 0000000000000000 CR3: 0000000d0520e001 CR4: 00000000001626f0
> >[12105.796976] Call Trace:
> >[12105.799446]  [<ffffffffac31d387>] bond_mii_monitor+0x497/0x6f0
> >[12105.805317]  [<ffffffffabd42643>] process_one_work+0x143/0x370
> >[12105.811225]  [<ffffffffabd42c7a>] worker_thread+0x4a/0x360
> >[12105.816761]  [<ffffffffabd48bc5>] kthread+0x105/0x140
> >[12105.821865]  [<ffffffffabd42c30>] ? rescuer_thread+0x380/0x380
> >[12105.827757]  [<ffffffffabd48ac0>] ? kthread_associate_blkcg+0xc0/0xc0
> >[12105.834266]  [<ffffffffac600241>] ret_from_fork+0x51/0x60
> >
> >Fixes: e2a7420df2e0 ("bonding/main: convert to using slave printk macros")
> >Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> >Reported-by: John Sperbeck <jsperbeck@...gle.com>
> >Cc: Jarod Wilson <jarod@...hat.com>
> >CC: Jay Vosburgh <j.vosburgh@...il.com>
> >CC: Veaceslav Falico <vfalico@...il.com>
> >CC: Andy Gospodarek <andy@...yhouse.net>
> >---
> > drivers/net/bonding/bond_main.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> >index a30595955a37a485b9e045a31969313f8336b668..84168455aded96dfd85b310841dee2a0d917b580 100644
> >--- a/drivers/net/bonding/bond_main.c
> >+++ b/drivers/net/bonding/bond_main.c
> >@@ -937,7 +937,7 @@ void bond_select_active_slave(struct bonding *bond)
> >                       return;
> >
> >               if (netif_carrier_ok(bond->dev))
> >-                      slave_info(bond->dev, best_slave->dev, "active interface up!\n");
> >+                      netdev_info(bond->dev, "active interface up!\n");
> >               else
> >                       netdev_info(bond->dev, "now running without any active interface!\n");
> >       }
>
>         What is the bonding mode and options in the failure case?

I am not sure.

Basically I only have crash dumps at this point (no idea how to repro the bug)

I guess that is :

Bonding Mode: IEEE 802.3ad Dynamic link aggregation
Transmit Hash Policy: encap3+4 (4)
Use Carrier: 1
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0
MAC address: 00:1a:11:c0:65:40
Active Members: eth1 eth2


>
>         I see that the fix is fine in the sense that it returns to the
> original status quo for the message.
>
>         However, the code path seems odd; if best_slave is NULL, that
> means that bond_find_best_slave() saw all slaves as down, but if
> netif_carrier_ok is true, then bond_set_carrier() did not.