Bug 2464381 (CVE-2026-31721)

Summary: CVE-2026-31721 kernel: usb: gadget: f_hid: move list and spinlock inits from bind to alloc
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's USB Human Interface Device (HID) gadget driver (`f_hid`). When a USB gadget is unbound and then rebound while file descriptors are still actively using its wait queues, the driver can re-initialize these queues while they still contain items. This can lead to list corruption, potentially causing system instability or a denial of service.
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Description OSIDB Bzimport 2026-05-01 15:03:31 UTC 
In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: f_hid: move list and spinlock inits from bind to alloc

There was an issue when you did the following:
- setup and bind an hid gadget
- open /dev/hidg0
- use the resulting fd in EPOLL_CTL_ADD
- unbind the UDC
- bind the UDC
- use the fd in EPOLL_CTL_DEL

When CONFIG_DEBUG_LIST was enabled, a list_del corruption was reported
within remove_wait_queue (via ep_remove_wait_queue). After some
debugging I found out that the queues, which f_hid registers via
poll_wait were the problem. These were initialized using
init_waitqueue_head inside hidg_bind. So effectively, the bind function
re-initialized the queues while there were still items in them.

The solution is to move the initialization from hidg_bind to hidg_alloc
to extend their lifetimes to the lifetime of the function instance.

Additionally, I found many other possibly problematic init calls in the
bind function, which I moved as well.
Comment 1 Keith Grant 2026-05-01 20:44:40 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050133-CVE-2026-31721-3c17@gregkh/T