kernel/drivers/usb/gadget/function/u_ncm.h, branch linux-rolling-stable

usb: gadget: f_ncm: Fix net_device lifecycle with device_move

2026-03-19T15:15:06Z

commit ec35c1969650e7cb6c8a91020e568ed46e3551b0 upstream. The network device outlived its parent gadget device during disconnection, resulting in dangling sysfs links and null pointer dereference problems. A prior attempt to solve this by removing SET_NETDEV_DEV entirely [1] was reverted due to power management ordering concerns and a NO-CARRIER regression. A subsequent attempt to defer net_device allocation to bind [2] broke 1:1 mapping between function instance and network device, making it impossible for configfs to report the resolved interface name. This results in a regression where the DHCP server fails on pmOS. Use device_move to reparent the net_device between the gadget device and /sys/devices/virtual/ across bind/unbind cycles. This preserves the network interface across USB reconnection, allowing the DHCP server to retain their binding. Introduce gether_attach_gadget()/gether_detach_gadget() helpers and use __free(detach_gadget) macro to undo attachment on bind failure. The bind_count ensures device_move executes only on the first bind. [1] https://lore.kernel.org/lkml/f2a4f9847617a0929d62025748384092e5f35cce.camel@crapouillou.net/ [2] https://lore.kernel.org/linux-usb/795ea759-7eaf-4f78-81f4-01ffbf2d7961@ixit.cz/ Fixes: 40d133d7f542 ("usb: gadget: f_ncm: convert to new function interface with backward compatibility") Cc: stable Signed-off-by: Kuen-Han Tsai Link: https://patch.msgid.link/20260309-f-ncm-revert-v2-7-ea2afbc7d9b2@google.com Signed-off-by: Greg Kroah-Hartman

Revert "usb: gadget: f_ncm: align net_device lifecycle with bind/unbind"

2026-03-19T15:15:06Z

commit 37893bc5de2460c543ec1aa8250c37a305234054 upstream. This reverts commit 56a512a9b4107079f68701e7d55da8507eb963d9. This commit is being reverted as part of a series-wide revert. By deferring the net_device allocation to the bind() phase, a single function instance will spawn multiple network devices if it is symlinked to multiple USB configurations. This causes regressions for userspace tools (like the postmarketOS DHCP daemon) that rely on reading the interface name (e.g., "usb0") from configfs. Currently, configfs returns the template "usb%d", causing the userspace network setup to fail. Crucially, because this patch breaks the 1:1 mapping between the function instance and the network device, this naming issue cannot simply be patched. Configfs only exposes a single 'ifname' attribute per instance, making it impossible to accurately report the actual interface name when multiple underlying network devices can exist for that single instance. All configurations tied to the same function instance are meant to share a single network device. Revert this change to restore the 1:1 mapping by allocating the network device at the instance level (alloc_inst). Reported-by: David Heidelberg Closes: https://lore.kernel.org/linux-usb/70b558ea-a12e-4170-9b8e-c951131249af@ixit.cz/ Fixes: 56a512a9b410 ("usb: gadget: f_ncm: align net_device lifecycle with bind/unbind") Cc: stable Signed-off-by: Kuen-Han Tsai Link: https://patch.msgid.link/20260309-f-ncm-revert-v2-3-ea2afbc7d9b2@google.com Signed-off-by: Greg Kroah-Hartman

Revert "usb: gadget: f_ncm: Fix atomic context locking issue"

2026-03-19T15:15:06Z

commit 11199720fac2debbe718aec11e026ab3330dc80d upstream. This reverts commit 0d6c8144ca4d93253de952a5ea0028c19ed7ab68. This commit is being reverted as part of a series-wide revert. By deferring the net_device allocation to the bind() phase, a single function instance will spawn multiple network devices if it is symlinked to multiple USB configurations. This causes regressions for userspace tools (like the postmarketOS DHCP daemon) that rely on reading the interface name (e.g., "usb0") from configfs. Currently, configfs returns the template "usb%d", causing the userspace network setup to fail. Crucially, because this patch breaks the 1:1 mapping between the function instance and the network device, this naming issue cannot simply be patched. Configfs only exposes a single 'ifname' attribute per instance, making it impossible to accurately report the actual interface name when multiple underlying network devices can exist for that single instance. All configurations tied to the same function instance are meant to share a single network device. Revert this change to restore the 1:1 mapping by allocating the network device at the instance level (alloc_inst). Reported-by: David Heidelberg Closes: https://lore.kernel.org/linux-usb/70b558ea-a12e-4170-9b8e-c951131249af@ixit.cz/ Fixes: 56a512a9b410 ("usb: gadget: f_ncm: align net_device lifecycle with bind/unbind") Cc: stable Signed-off-by: Kuen-Han Tsai Link: https://patch.msgid.link/20260309-f-ncm-revert-v2-1-ea2afbc7d9b2@google.com Signed-off-by: Greg Kroah-Hartman

usb: gadget: f_ncm: Fix atomic context locking issue

2026-03-19T15:15:05Z

commit 0d6c8144ca4d93253de952a5ea0028c19ed7ab68 upstream. The ncm_set_alt function was holding a mutex to protect against races with configfs, which invokes the might-sleep function inside an atomic context. Remove the struct net_device pointer from the f_ncm_opts structure to eliminate the contention. The connection state is now managed by a new boolean flag to preserve the use-after-free fix from commit 6334b8e4553c ("usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error"). BUG: sleeping function called from invalid context Call Trace: dump_stack_lvl+0x83/0xc0 dump_stack+0x14/0x16 __might_resched+0x389/0x4c0 __might_sleep+0x8e/0x100 ... __mutex_lock+0x6f/0x1740 ... ncm_set_alt+0x209/0xa40 set_config+0x6b6/0xb40 composite_setup+0x734/0x2b40 ... Fixes: 56a512a9b410 ("usb: gadget: f_ncm: align net_device lifecycle with bind/unbind") Cc: stable@kernel.org Signed-off-by: Kuen-Han Tsai Link: https://patch.msgid.link/20260221-legacy-ncm-v2-2-dfb891d76507@google.com Signed-off-by: Greg Kroah-Hartman

usb: gadget: f_ncm: align net_device lifecycle with bind/unbind

2026-03-12T11:09:26Z

[ Upstream commit 56a512a9b4107079f68701e7d55da8507eb963d9 ] Currently, the net_device is allocated in ncm_alloc_inst() and freed in ncm_free_inst(). This ties the network interface's lifetime to the configuration instance rather than the USB connection (bind/unbind). This decoupling causes issues when the USB gadget is disconnected where the underlying gadget device is removed. The net_device can outlive its parent, leading to dangling sysfs links and NULL pointer dereferences when accessing the freed gadget device. Problem 1: NULL pointer dereference on disconnect Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Call trace: __pi_strlen+0x14/0x150 rtnl_fill_ifinfo+0x6b4/0x708 rtmsg_ifinfo_build_skb+0xd8/0x13c rtmsg_ifinfo+0x50/0xa0 __dev_notify_flags+0x4c/0x1f0 dev_change_flags+0x54/0x70 do_setlink+0x390/0xebc rtnl_newlink+0x7d0/0xac8 rtnetlink_rcv_msg+0x27c/0x410 netlink_rcv_skb+0x134/0x150 rtnetlink_rcv+0x18/0x28 netlink_unicast+0x254/0x3f0 netlink_sendmsg+0x2e0/0x3d4 Problem 2: Dangling sysfs symlinks console:/ # ls -l /sys/class/net/ncm0 lrwxrwxrwx ... /sys/class/net/ncm0 -> /sys/devices/platform/.../gadget.0/net/ncm0 console:/ # ls -l /sys/devices/platform/.../gadget.0/net/ncm0 ls: .../gadget.0/net/ncm0: No such file or directory Move the net_device allocation to ncm_bind() and deallocation to ncm_unbind(). This ensures the network interface exists only when the gadget function is actually bound to a configuration. To support pre-bind configuration (e.g., setting interface name or MAC address via configfs), cache user-provided options in f_ncm_opts using the gether_opts structure. Apply these cached settings to the net_device upon creation in ncm_bind(). Preserve the use-after-free fix from commit 6334b8e4553c ("usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error"). Check opts->net in ncm_set_alt() and ncm_disable() to ensure gether_disconnect() runs only if a connection was established. Fixes: 40d133d7f542 ("usb: gadget: f_ncm: convert to new function interface with backward compatibility") Cc: stable@kernel.org Signed-off-by: Kuen-Han Tsai Link: https://patch.msgid.link/20251230-ncm-refactor-v1-3-793e347bc7a7@google.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin

usb: gadget: ncm: Add support to update wMaxSegmentSize via configfs

2024-01-04T15:01:14Z

The max segment size is currently limited to the ethernet frame length of the kernel which happens to be 1514 at this point in time. However the NCM specification limits it to 64K for sixtenn bit NTB's. For peer to peer connections, increasing the segment size gives better throughput. Add support to configure this value before configfs symlink is created. Also since the NTB Out/In buffer sizes are fixed at 16384 bytes, limit the segment size to an upper cap of 8000 to allow at least a minimum of 2 MTU sized datagrams to be aggregated. Set the default MTU size for the ncm interface during function bind before network interface is registered allowing MTU to be set in parity with wMaxSegmentSize. Update gadget documentation describing the new configfs property. Signed-off-by: Krishna Kurapati Link: https://lore.kernel.org/r/20231221153216.18657-1-quic_kriskura@quicinc.com Signed-off-by: Greg Kroah-Hartman

USB: gadget: Use the correct style for SPDX License Identifier

2020-05-05T07:58:49Z

This patch corrects the SPDX License Identifier style in header files related to USB peripheral controller drivers. For C header files Documentation/process/license-rules.rst mandates C-like comments (opposed to C source files where C++ style should be used). Changes made by using a script provided by Joe Perches here: https://lkml.org/lkml/2019/2/7/46. Suggested-by: Joe Perches Signed-off-by: Nishad Kamdar Signed-off-by: Felipe Balbi

usb: gadget: f_ncm: Add OS descriptor support

2019-05-03T06:13:47Z

To be able to use the default USB class drivers available in Microsoft Windows, we need to add OS descriptors to the exported USB gadget to tell the OS that we are compatible with the built-in drivers. Copy the OS descriptor support from f_rndis into f_ncm. As a result, using the WINNCM compatible ID, the UsbNcm driver is loaded on enumeration without the need for a custom driver or inf file. Signed-off-by: Romain Izard Signed-off-by: Felipe Balbi

usb: gadget: Change Andrzej Pietrasiewicz's e-mail address

2019-02-11T09:12:29Z

My @samusung.com address is going to cease existing soon, so change it to an address which can actually be used to contact me. Signed-off-by: Andrzej Pietrasiewicz Signed-off-by: Felipe Balbi

USB: gadget: function: Remove redundant license text

2017-11-07T14:45:02Z

Now that the SPDX tag is in all USB files, that identifies the license in a specific and legally-defined manner. So the extra GPL text wording can be removed as it is no longer needed at all. This is done on a quest to remove the 700+ different ways that files in the kernel describe the GPL license text. And there's unneeded stuff like the address (sometimes incorrect) for the FSF which is never needed. No copyright headers or other non-license-description text was removed. Cc: Oliver Neukum Cc: Johan Hovold Cc: Jerry Zhang Cc: John Keeping Cc: Krzysztof Opasiak Cc: Abdulhadi Mohamed Cc: Matthew Wilcox Cc: Janusz Dziedzic Acked-by: Felipe Balbi Acked-by: Michal Nazarewicz Acked-by: Laurent Pinchart Acked-by: Vincent Pelletier Signed-off-by: Greg Kroah-Hartman