CVE-2026-68090

In the Linux kernel, the following vulnerability has been resolved:

debugobjects: Plug race against a concurrent OOM disable

syzbot reported a puzzling splat:

WARNING: kernel/time/hrtimer.c:443 at stub_timer+0xa/0x20

stub_timer() is installed as timer callback function in hrtimer_fixup_assert_init(), which is invoked when debug_object_assert_init() cant find a shadow object. In that case debug objects emits a warning about it before invoking the fixup.

Though the provided console log lacks this warning and instead has the following a few seconds before the splat:

 ODEBUG: Out of memory. ODEBUG disabled

So the object was looked up in debug_object_assert_init() and the lookup failed due a concurrent out of memory situation which disabled debug objects and freed the shadow objects:

debug_object_assert_init() if (!debug_objects_enabled) return; obj = alloc(); if (!obj) { // Out of memory debug_objects_enabled = false; free_objects(); obj = lookup_or_alloc();

    // The lookup failed because the other side
    // removed the objects, so this returns
    // an error code as the object in question
    // is not statically initialized

if (!IS_ERR_OR_NULL(obj))
    	return;
    if (!obj) {
    	debug_oom();
            return;
    }

    print(...)
       if (!debug_objects_enabled)
            return;

    fixup(...)

The debug object splat is skipped because debug_objects_enabled is false, but the fixup callback is invoked unconditionally, which makes the timer disfunctional.

This is only a problem in debug_object_assert_init() and debug_object_activate() as both have to handle statically initialized objects and therefore must handle the error pointer return case gracefully. All other places only handle the found/not found case and the NULL pointer return is a signal for OOM. Otherwise they get a valid shadow object.

Plug the hole by checking whether debug objects are still enabled before invoking the print and fixup function in those two places.

Affected Software

References

• https://git.kernel.org/stable/c/1f4f02b336c3be125c8fcf87df73db2e0e028b8b
• https://git.kernel.org/stable/c/203a965bf2ab43130778d8214fb0c3c8c2d19cdf
• https://git.kernel.org/stable/c/23da32e88627e63e0864f59f4c63a2dc0ab851a3
• https://git.kernel.org/stable/c/2d5e320b7ab9b25229ac4331541964a58b5e1d29
• https://git.kernel.org/stable/c/b81dde13cc163450dcb402dcc915ef13ba241e01
• https://git.kernel.org/stable/c/c00164c9e7fa6145886ad666806cb5347895de5c
• https://git.kernel.org/stable/c/d663fbf28b2eebe665bb9cf828d7d528e5a8707e
• https://git.kernel.org/stable/c/e2e255d07723c330dded8e576ce28a8d23a692ce