CVE-2026-43073

Published May 5, 2026

Last updated 3 days ago

CVSS medium 5.5

Overview

Description
In the Linux kernel, the following vulnerability has been resolved: x86-64: rename misleadingly named '__copy_user_nocache()' function This function was a masterclass in bad naming, for various historical reasons. It claimed to be a non-cached user copy. It is literally _neither_ of those things. It's a specialty memory copy routine that uses non-temporal stores for the destination (but not the source), and that does exception handling for both source and destination accesses. Also note that while it works for unaligned targets, any unaligned parts (whether at beginning or end) will not use non-temporal stores, since only words and quadwords can be non-temporal on x86. The exception handling means that it _can_ be used for user space accesses, but not on its own - it needs all the normal "start user space access" logic around it. But typically the user space access would be the source, not the non-temporal destination. That was the original intention of this, where the destination was some fragile persistent memory target that needed non-temporal stores in order to catch machine check exceptions synchronously and deal with them gracefully. Thus that non-descriptive name: one use case was to copy from user space into a non-cached kernel buffer. However, the existing users are a mix of that intended use-case, and a couple of random drivers that just did this as a performance tweak. Some of those random drivers then actively misused the user copying version (with STAC/CLAC and all) to do kernel copies without ever even caring about the exception handling, _just_ for the non-temporal destination. Rename it as a first small step to actually make it halfway sane, and change the prototype to be more normal: it doesn't take a user pointer unless the caller has done the proper conversion, and the argument size is the full size_t (it still won't actually copy more than 4GB in one go, but there's also no reason to silently truncate the size argument in the caller). Finally, use this now sanely named function in the NTB code, which mis-used a user copy version (with STAC/CLAC and all) of this interface despite it not actually being a user copy at all.
Source
416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status
Modified
Products
linux_kernel

Risk scores

CVSS 3.1

Type
Primary
Base score
5.5
Impact score
3.6
Exploitability score
1.8
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Severity
MEDIUM

Weaknesses

nvd@nist.gov
NVD-CWE-noinfo

Social media

Hype score
Not currently trending

Configurations

Related CVEs

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  2. In the Linux kernel, the following vulnerability has been resolved: cgroup: Avoid iteration of dying tasks with zero refcount The commit 260fbcb92bbea ("cgroup: Move dying_tasks cleanup from cgroup_task_release() to cgroup_task_free()") extended the lifetime of tasks on the dying_tasks list. The iterators have provision to go through dying_tasks because of dying threadgroup leaders or explicit CSS_TASK_ITER_WITH_DEAD, however, it was expected that such tasks can obtain a new reference (that is possible before cgroup_task_release()/put_task_struct_rcu_user()). The tasks after cgroup_task_release() and before cgroup_task_free() are subject to race when they may or may not have ->usage count > 0. The race window is between css_task_iter_next() invocations when css_set_lock is released and we may arrive at a new ->task_pos. The iterator should not attempt to resurrect tasks whose ->usage count dropped to zero. (When that happens, __put_task_struct_rcu_cb() is already imminent and the returned task_struct would could be used after free.) As for the fix, we cannot simply check the signal->live count of a task on the dying list because that won't distinguish regular zombies waiting to be reaped from RCU remnant tasks that are going to be free'd. Therefore add an extra check to rule out ->usage==0 tasks from any iteration. The repeat: loop in css_task_iter_advance() doesn't consider ->usage count, so add a new loop to css_task_iter_next() to skip de-used tasks on the dying_list. Rough illustration of the possible race R (reader of cgroup.procs) T (thread) L (group leader) --------------------------------- -------------------------------- -------------------------------- L exits, signal->live > 0 cgroup_task_dead(L) css_set_skip_task_iters() // skips only cset->tasks list_add_tail(&L->cg_list, &cset->dying_tasks) css_task_iter_next() take css_set_lock css_task_iter_advance() leader && signal->live != 0 => it->task_pos = &L->cg_list release css_set_lock T exits --signal->live == 0 cgroup_task_dead(T) // css_set_lock release_task(T) cgroup_task_release(T) release_task(L) // zap_leader cgroup_task_release(L) put_task_struct_rcu_user(L) ...RCU... put_task_struct(L) L->usage = 0 /* L still on dying_tasks */ ...RCU... __put_task_struct(L) css_task_iter_next() // another iteration take css_set_lock it->task_pos = &L->cg_list get_task_struct(L) => addition on 0 drop css_set_lock cgroup_task_free(L) css_set_skip_task_iters() // dying skip comes too late free_task(L) cgroup_procs_show() task_pid_vnr(L)•CVE-2026-98163
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References

Sources include official advisories and independent security research.