Re: [PATCH net] net: annotate data race around dev->flags in __dev_change_flags

[Eric Dumazet]

On Mon, Jul 29, 2024 at 6:34 PM Jeongjun Park <aha310510@xxxxxxxxx> wrote:
>
> According to KCSAN report, there is a read/write race between
> __dev_change_flags and netif_is_bond_master for dev->flags.
>
> Thereforce, __dev_change_flags() needs protection.
>
> <syzbot>
> BUG: KCSAN: data-race in __dev_change_flags / is_upper_ndev_bond_master_filter
>
> read-write to 0xffff888112d970b0 of 4 bytes by task 4888 on cpu 0:
>  __dev_change_flags+0x9a/0x410 net/core/dev.c:8755
>  rtnl_configure_link net/core/rtnetlink.c:3321 [inline]
>  rtnl_newlink_create net/core/rtnetlink.c:3518 [inline]
>  __rtnl_newlink net/core/rtnetlink.c:3730 [inline]
>  rtnl_newlink+0x121e/0x1690 net/core/rtnetlink.c:3743
>  rtnetlink_rcv_msg+0x85e/0x910 net/core/rtnetlink.c:6635
>  netlink_rcv_skb+0x12c/0x230 net/netlink/af_netlink.c:2564
>  rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:6653
>  netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
>  netlink_unicast+0x58d/0x660 net/netlink/af_netlink.c:1361
>  netlink_sendmsg+0x5ca/0x6e0 net/netlink/af_netlink.c:1905
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg+0x140/0x180 net/socket.c:745
>  ____sys_sendmsg+0x312/0x410 net/socket.c:2585
>  ___sys_sendmsg net/socket.c:2639 [inline]
>  __sys_sendmsg+0x1e9/0x280 net/socket.c:2668
>  __do_sys_sendmsg net/socket.c:2677 [inline]
>  __se_sys_sendmsg net/socket.c:2675 [inline]
>  __x64_sys_sendmsg+0x46/0x50 net/socket.c:2675
>  x64_sys_call+0xb25/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:47
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> read to 0xffff888112d970b0 of 4 bytes by task 11 on cpu 1:
>  netif_is_bond_master include/linux/netdevice.h:5020 [inline]
>  is_upper_ndev_bond_master_filter+0x2b/0xb0 drivers/infiniband/core/roce_gid_mgmt.c:275
>  ib_enum_roce_netdev+0x124/0x1d0 drivers/infiniband/core/device.c:2310
>  ib_enum_all_roce_netdevs+0x8a/0x100 drivers/infiniband/core/device.c:2337
>  netdevice_event_work_handler+0x15b/0x3c0 drivers/infiniband/core/roce_gid_mgmt.c:626
>  process_one_work kernel/workqueue.c:3248 [inline]
>  process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3329
>  worker_thread+0x526/0x720 kernel/workqueue.c:3409
>  kthread+0x1d1/0x210 kernel/kthread.c:389
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> value changed: 0x00001002 -> 0x00000202
>
> Reported-by: syzbot+113b65786d8662e21ff7@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
> ---
>  net/core/dev.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 6ea1d20676fb..3b9626cdfd9a 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -8799,7 +8799,7 @@ EXPORT_SYMBOL(dev_get_flags);
>  int __dev_change_flags(struct net_device *dev, unsigned int flags,
>                        struct netlink_ext_ack *extack)
>  {
> -       unsigned int old_flags = dev->flags;
> +       unsigned int old_flags = READ_ONCE(dev->flags);
>         int ret;
>
>         ASSERT_RTNL();
> @@ -8808,12 +8808,13 @@ int __dev_change_flags(struct net_device *dev, unsigned int flags,
>          *      Set the flags on our device.
>          */
>
> -       dev->flags = (flags & (IFF_DEBUG | IFF_NOTRAILERS | IFF_NOARP |
> -                              IFF_DYNAMIC | IFF_MULTICAST | IFF_PORTSEL |
> -                              IFF_AUTOMEDIA)) |
> -                    (dev->flags & (IFF_UP | IFF_VOLATILE | IFF_PROMISC |
> -                                   IFF_ALLMULTI));
> +       unsigned int new_flags = (flags & (IFF_DEBUG | IFF_NOTRAILERS | IFF_NOARP |
> +                                          IFF_DYNAMIC | IFF_MULTICAST | IFF_PORTSEL |
> +                                          IFF_AUTOMEDIA)) |
> +                                (READ_ONCE(dev->flags) & (IFF_UP | IFF_VOLATILE | IFF_PROMISC |
> +                                               IFF_ALLMULTI));
>
> +       WRITE_ONCE(dev->flags, new_flags);
>         /*
>          *      Load in the correct multicast list now the flags have changed.
>          */
> @@ -8839,12 +8840,12 @@ int __dev_change_flags(struct net_device *dev, unsigned int flags,
>
>         if ((flags ^ dev->gflags) & IFF_PROMISC) {
>                 int inc = (flags & IFF_PROMISC) ? 1 : -1;
> -               unsigned int old_flags = dev->flags;
> +               unsigned int old_flags = READ_ONCE(dev->flags);
>
>                 dev->gflags ^= IFF_PROMISC;
>
>                 if (__dev_set_promiscuity(dev, inc, false) >= 0)
> -                       if (dev->flags != old_flags)
> +                       if (READ_ONCE(dev->flags) != old_flags)
>                                 dev_set_rx_mode(dev);
>         }
>

These READ_ONCE() in RTNL protected regions are not necessary, because
dev->flags can not be changed by another thread.