Re: [PATCH net v2] net: devmem: fix kernel panic when socket close after module unload

[Jakub Kicinski <kuba@kernel.org>]

On Tue,  6 May 2025 14:08:58 +0000 Taehee Yoo wrote:
> Kernel panic occurs when a devmem TCP socket is closed after NIC module
> is unloaded.
> 
> This is Devmem TCP unregistration scenarios. number is an order.
> (a)socket close    (b)pp destroy    (c)uninstall    result
> 1                  2                3               OK
> 1                  3                2               (d)Impossible
> 2                  1                3               OK
> 3                  1                2               (e)Kernel panic
> 2                  3                1               (d)Impossible
> 3                  2                1               (d)Impossible
> 
> (a) netdev_nl_sock_priv_destroy() is called when devmem TCP socket is
>     closed.
> (b) page_pool_destroy() is called when the interface is down.
> (c) mp_ops->uninstall() is called when an interface is unregistered.
> (d) There is no scenario in mp_ops->uninstall() is called before
>     page_pool_destroy().
>     Because unregister_netdevice_many_notify() closes interfaces first
>     and then calls mp_ops->uninstall().
> (e) netdev_nl_sock_priv_destroy() accesses struct net_device to acquire
>     netdev_lock().
>     But if the interface module has already been removed, net_device
>     pointer is invalid, so it causes kernel panic.
> 
> In summary, there are only 3 possible scenarios.
>  A. sk close -> pp destroy -> uninstall.
>  B. pp destroy -> sk close -> uninstall.
>  C. pp destroy -> uninstall -> sk close.
> 
> Case C is a kernel panic scenario.
> 
> In order to fix this problem, It makes mp_dmabuf_devmem_uninstall() set
> binding->dev to NULL.
> It indicates an bound net_device was unregistered.
> 
> It makes netdev_nl_sock_priv_destroy() do not acquire netdev_lock()
> if binding->dev is NULL.
> 
> It inverts socket/netdev lock order like below:
>     netdev_lock();
>     mutex_lock(&priv->lock);
>     mutex_unlock(&priv->lock);
>     netdev_unlock();
> 
> Because of inversion of locking ordering, mp_dmabuf_devmem_uninstall()
> acquires socket lock from now on.
> 
> Tests:
> Scenario A:
>     ./ncdevmem -s 192.168.1.4 -c 192.168.1.2 -f $interface -l -p 8000 \
>         -v 7 -t 1 -q 1 &
>     pid=$!
>     sleep 10
>     kill $pid
>     ip link set $interface down
>     modprobe -rv $module
> 
> Scenario B:
>     ./ncdevmem -s 192.168.1.4 -c 192.168.1.2 -f $interface -l -p 8000 \
>         -v 7 -t 1 -q 1 &
>     pid=$!
>     sleep 10
>     ip link set $interface down
>     kill $pid
>     modprobe -rv $module
> 
> Scenario C:
>     ./ncdevmem -s 192.168.1.4 -c 192.168.1.2 -f $interface -l -p 8000 \
>         -v 7 -t 1 -q 1 &
>     pid=$!
>     sleep 10
>     modprobe -rv $module
>     sleep 5
>     kill $pid
> 
> Splat looks like:
> Oops: general protection fault, probably for non-canonical address 0xdffffc001fffa9f7: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
> KASAN: probably user-memory-access in range [0x00000000fffd4fb8-0x00000000fffd4fbf]
> CPU: 0 UID: 0 PID: 2041 Comm: ncdevmem Tainted: G    B   W           6.15.0-rc1+ #2 PREEMPT(undef)  0947ec89efa0fd68838b78e36aa1617e97ff5d7f
> Tainted: [B]=BAD_PAGE, [W]=WARN
> RIP: 0010:__mutex_lock (./include/linux/sched.h:2244 kernel/locking/mutex.c:400 kernel/locking/mutex.c:443 kernel/locking/mutex.c:605 kernel/locking/mutex.c:746)
> Code: ea 03 80 3c 02 00 0f 85 4f 13 00 00 49 8b 1e 48 83 e3 f8 74 6a 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 34 48 89 fa 48 c1 ea 03 <0f> b6 f
> RSP: 0018:ffff88826f7ef730 EFLAGS: 00010203
> RAX: dffffc0000000000 RBX: 00000000fffd4f88 RCX: ffffffffaa9bc811
> RDX: 000000001fffa9f7 RSI: 0000000000000008 RDI: 00000000fffd4fbc
> RBP: ffff88826f7ef8b0 R08: 0000000000000000 R09: ffffed103e6aa1a4
> R10: 0000000000000007 R11: ffff88826f7ef442 R12: fffffbfff669f65e
> R13: ffff88812a830040 R14: ffff8881f3550d20 R15: 00000000fffd4f88
> FS:  0000000000000000(0000) GS:ffff888866c05000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000563bed0cb288 CR3: 00000001a7c98000 CR4: 00000000007506f0
> PKRU: 55555554
> Call Trace:
> <TASK>
>  ...
>  netdev_nl_sock_priv_destroy (net/core/netdev-genl.c:953 (discriminator 3))
>  genl_release (net/netlink/genetlink.c:653 net/netlink/genetlink.c:694 net/netlink/genetlink.c:705)
>  ...
>  netlink_release (net/netlink/af_netlink.c:737)
>  ...
>  __sock_release (net/socket.c:647)
>  sock_close (net/socket.c:1393)

I'll look at the code later today, but it will need a respin for sure:

net/core/netdev-genl.c: In function ‘netdev_nl_bind_rx_doit’:
net/core/netdev-genl.c:878:61: error: passing argument 3 of ‘net_devmem_bind_dmabuf’ from incompatible pointer type [-Werror=incompatible-pointer-types]
  878 |         binding = net_devmem_bind_dmabuf(netdev, dmabuf_fd, priv, info->extack);
      |                                                             ^~~~
      |                                                             |
      |                                                             struct netdev_nl_sock *
In file included from ../net/core/netdev-genl.c:16:
net/core/devmem.h:133:48: note: expected ‘struct netlink_ext_ack *’ but argument is of type ‘struct netdev_nl_sock *’
  133 |                        struct netlink_ext_ack *extack)
      |                        ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
net/core/netdev-genl.c:878:19: error: too many arguments to function ‘net_devmem_bind_dmabuf’
  878 |         binding = net_devmem_bind_dmabuf(netdev, dmabuf_fd, priv, info->extack);
      |                   ^~~~~~~~~~~~~~~~~~~~~~
In file included from ../net/core/netdev-genl.c:16:
net/core/devmem.h:132:1: note: declared here
  132 | net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
      | ^~~~~~~~~~~~~~~~~~~~~~

This is on the kunit build so guessing some compat was missed.