linux-stable.git/kernel, branch v7.1.12

futex: Avoid private hash use-after-free on final put

2026-08-27T12:34:41+00:00

[ Upstream commit 1c7efabfbaf796f11000a46094a69955a01ec6cc ]

futex_private_hash_put() drops the reference to fph before evaluating
fph->mm for wake_up_var(). futex_ref_put() enables preemption again before
returning. If that put drops the final reference and the task is preempted,
another task can pivot to the replacement hash and free the old hash after
an RCU grace period. The first task then reads fph->mm from the freed
allocation when it resumes.

KASAN reports a slab-use-after-free in futex_private_hash_put(), with the
read at offset 24 in a freed kmalloc-512 allocation. The allocation and
free stacks point to futex_hash_allocate() and the RCU free path,
respectively.

Load the mm pointer while the fph reference is still held and pass the
saved value to wake_up_var(). wake_up_var() uses the pointer as a waitqueue
key and does not dereference the mm through it.

Fixes: bd54df5ea7ca ("futex: Allow to resize the private local hash")
Signed-off-by: Felix Hoffmann 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260731155024.1150011-1-f3lix.dev@gmx.de
[ dropped the `!fph` NULL guard since this tree's callers already check, keeping the existing `if (futex_ref_put(fph))` form ]
Signed-off-by: Sasha Levin

futex: Fix might_sleep() warning in futex_pivot_pending()

2026-08-27T12:34:39+00:00

commit d8aa5dd97944a72d4a9e3cc79bb80fcac7d6e829 upstream.

A younger me put a WARN in might_sleep() to warn about nested sleep loops. This
younger me also build a wait-loop variant that can deal with it. This wait-loop
variant doesn't have all the fancy wrappers, since it isn't used much. It also
lacks wait-bit support.

Add the wait-bit support and use it to fix the nested wait issue.

Fixes: 8e7ff730dd96 ("futex: Fix race in futex_pivot_pending() during private hash resize")
Reported-by: syzbot+350a93852ac854927f45@syzkaller.appspotmail.com
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Thomas Gleixner 
Link: https://patch.msgid.link/20260820074927.GH1246887@noisy.programming.kicks-ass.net
Closes: https://syzkaller.appspot.com/bug?extid=350a93852ac854927f45
Signed-off-by: Greg Kroah-Hartman

futex: Fix race on the initial mm->futex.phash.ref allocation

2026-08-27T12:34:39+00:00

commit bde0238083647381d4747355c5a19115a3422b96 upstream.

futex_hash_allocate() allocates mm->futex.phash.ref without any locking.
Commit d9b05321e21e ("futex: Move futex_hash_free() back to __mmput()")
moved the allocation here and assumed that the process has just a single
thread at this point.

Commit ee9dce44362b ("futex: Drop CLONE_THREAD requirement for private
default hash alloc") widened need_futex_hash_allocate_default() to cover
any CLONE_VM clone, but left out vfork because the parent is suspended and
cannot race.

That no longer holds once vfork is nested. If a vfork child calls vfork
again and is then killed with SIGKILL, the parent is released from its
vfork wait and runs concurrently with the grandchild in the same mm.
Neither of them went through futex_hash_allocate_default().

When both call prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS) at the same
time, each one sees mm->futex.phash.ref as NULL and stores its own percpu
counter. Only the last store survives. The counter stored first is no
longer reachable from the mm, so the references on it are not seen by
__futex_ref_atomic_end(). A private hash that still has references is then
considered dead and freed, and a task that still holds one of its buckets
writes into freed memory in futex_q_lock().

Store the counter once with cmpxchg() and let the loser free_percpu() its
own. The initial reference has to be taken before the store, otherwise
another task can install a private hash while the counter is still 0.

Fixes: d9b05321e21e ("futex: Move futex_hash_free() back to __mmput()")
Signed-off-by: Hyunwoo Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Thomas Gleixner 
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/ansrpP4ImE1MaBY9@v4bel
Signed-off-by: Greg Kroah-Hartman

futex: Fix race in futex_pivot_pending() during private hash resize

2026-08-27T12:34:39+00:00

commit 8e7ff730dd96519a333d1570edf1c3fabb6d3629 upstream.

A task performing a custom private hash resize can remain blocked in
uninterruptible sleep indefinitely.  The hung-task detector reports:

  INFO: task futex-resizer:314 blocked for more than 10 seconds.
  task:futex-resizer state:D stack:14824 pid:314 tgid:312 ppid:311

  Call Trace:
   __schedule+0x521/0xf30
   schedule+0x22/0xa0
   futex_hash_allocate+0x3db/0x490
   __do_sys_prctl+0x6f5/0xbd0
   do_syscall_64+0xf9/0x530
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

  Kernel panic - not syncing: hung_task: blocked tasks

futex_pivot_pending() allows the resize request to continue when
either no replacement hash is pending (hash_new == NULL) or the current
hash reference count has reached zero.

After the final-reference wake, another futex task can complete the
pivot between the two observations:

  T1                                  T2

  futex_hash_allocate()
    wait_var_event(mm, ...)
      futex_pivot_pending(mm)
        hash_new != NULL
                                      futex_hash()
                                        futex_ref_get(old) -> false
                                        futex_pivot_hash(mm)
                                          hash_new = NULL
                                          __futex_pivot_hash(mm, new)
                                            rcu_assign_pointer(hash, new)
        fph = rcu_dereference(hash) /* new */
        futex_ref_is_dead(fph) -> false
      schedule()

The pivot changes the state from hash_new != NULL with a dead current
hash to hash_new == NULL with a live current hash.  Because
futex_pivot_pending() reads hash_new and hash without serialization,
the resize task can observe hash_new in the pre-pivot state and hash in
the post-pivot state, causing futex_pivot_pending() to return false even
though the pivot has completed.  The task then goes to sleep after the
wakeup has already been consumed.

Serialize state reads in futex_pivot_pending() using futex_mm_phash::lock.
This guarantees that futex_pivot_pending() observes hash_new and hash
atomically, eliminating the race condition.

Fixes: bd54df5ea7ca ("futex: Allow to resize the private local hash")
Suggested-by: Peter Zijlstra 
Signed-off-by: Yao Kai 
Signed-off-by: Thomas Gleixner 
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260804125530.3933754-1-yaokai34@huawei.com
Signed-off-by: Greg Kroah-Hartman

futex/pi: Plug private futex exec() race

2026-08-27T12:34:39+00:00

commit c5f0bc9fd1cec4a00400cc727fcde03e0fde17cc upstream.

The check for private futexes whether the waiter's mm, which is stored in
the futex_key and copied into the pi_state, is the same as the owner's mm
is not sufficient for exec(). exec() has a gap where the mm check fails to
give the correct answer:

  exec()
  ...
    exec_release_mm()
      futex_exec_release()
        tsk::futex::exit_state = EXITING;
        cleanup_robust_list();
1)      tsk::futex::exit_state = OK;
    ...
    old_mm = tsk::mm;
2)  tsk::mm = ->mm;

Between #1 and #2 the check for the mm is wrong as that mm is about to be
swapped out and eventually freed.

Plug this gap by:

  1) Setting tsk::futex::exit_state to FUTEX_STATE_DEAD in
     futex_exec_release()

  2) Setting tsk::futex::exit_state to FUTEX_STATE_OK after
     the mm has been switched.

>>From a futex point of view the task is dead after it finished the robust
list cleanup up to the point where it sets the state to OK again.

Fixes: 80367ad01d93 ("futex: Add basic infrastructure for local task local hash")
Signed-off-by: Thomas Gleixner 
Reviewed-by: Kyle Zeng 
Acked-by: Peter Zijlstra 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex: Sanitize and document task_struct::futex::state transitions

2026-08-27T12:34:39+00:00

commit f9ece060cc43eae8a1f148737d193ba0d07b8f88 upstream.

The futex state is used to prevent a waiter from attaching to the lock
owner while the owner runs the futex cleanup in exit() or exec().

Only the state transition from FUTEX_STATE_OK to FUTEX_STATE_EXITING must
be done with the task's pi_lock held, the transition away from
FUTEX_STATE_EXITING has no serialization requirements on the writer side,
but it's completely non obvious why. It's magically protected by
exit_pi_state(), which operates under tsk::pi_lock, as that's the state
which has to be correct when the waiter observes the new state.

OTOH, taking the pi_lock in futex_cleanup_end() is not a performance issue
because at that point the lock should be uncontended in the vast majority
of cases.

Aside of that the handling of FUTEX_STATE_EXITING in attach_to_pi_owner()
and handle_exit_race() is confusing at best.

Protect the store in futex_cleanup_end() with tsk::pi_lock, handle
FUTEX_STATE_EXITING in attach_to_pi_owner() explicitly and document how
this is supposed to work.

Reported-by: Peter Zijlstra 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Kyle Zeng 
Acked-by: Peter Zijlstra 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex/pi: Reject cross-mm private futex owners

2026-08-27T12:34:39+00:00

commit 59b3732f95dda1fbd2234514d35f4fb6b5bb6d85 upstream.

A private futex key borrows the waiter's mm without taking an mm_users
reference. Nevertheless, attach_to_pi_owner() currently accepts an owner
from a different address space and copies the private key into the owner's
PI state.

When that owner exits, exit_pi_state_list() uses the saved key to find the
hash bucket and acquires a reference to the waiter's private hash. If the
last user of the waiter's mm exits concurrently, futex_hash_free() frees
the hash while the owner still uses its bucket and reference.

Prevent this by validating in attach_to_pi_owner() that, for private
futexes, the owner mm and waiter mm are the same. Perform the check with
the owner's pi_lock held and after validating owner::futex::state to
serialize against a concurrent PI-state exit cleanup.

[ tglx: Amended comment ]

Fixes: 80367ad01d93 ("futex: Add basic infrastructure for local task local hash")
Signed-off-by: Kyle Zeng 
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Assisted-by: Codex:gpt-5.6-sol
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

kcov: fix data corruption and race conditions on PREEMPT_RT

2026-08-27T12:34:36+00:00

commit 2eed77fdcb0cc48e8eccb2bcd4b7f2c6d650e84c upstream.

syzbot is reporting KCOV state corruption on PREEMPT_RT kernels, for the
temporary storage used for saving/restoring remote KCOV state is currently
allocated as the per-CPU area.

On PREEMPT_RT kernels, softirq handlers run as preemptible task threads
(e.g., ksoftirqd). If a softirq context preempts a task running a remote
KCOV session, it safely saves the task's state into the per-CPU area.
However, if that softirq thread is subsequently preempted by a higher-
priority softirq thread on the same CPU, the second softirq will overwrite
the same per-CPU area, permanently destroying the original task's KCOV
state.

Fix this data corruption by moving the temporary storage from the per-CPU
area to the per-thread area. Since each softirq thread now owns its own
task context, nested softirq preemption no longer causes data overwrites.

Note that while the temporary storage is now on a per-thread basis, the
per-CPU kcov_percpu_data.lock must be retained, for we need to ensure that
kcov_remote_start() and kcov_remote_stop() operate atomically without
racing against asynchronous interrupts that manipulate the current task's
KCOV state.

It is likely that GFP_KERNEL allocation by vmalloc_node() in kcov_init()
has already called panic() before returning NULL, for there will be no
OOM-killable userspace processes when __init function of built-in module
runs. But this patch also fixes crashing the kernel when vmalloc_node()
in kcov_init() returned NULL, for kcov_init() left per-CPU irq_area == NULL
but kcov_remote_start() depends on per-CPU irq_area != NULL, resulting in

  (1) doing vmalloc() in kcov_remote_start() despite !in_task() context

  (2) out-of-array-bounds access if (1) succeeded but
      kcov->remote_size < CONFIG_KCOV_IRQ_AREA_SIZE

  (3) always leak memory allocated by (1), eventually killing all
      OOM-killable userspace processes

problems.

Link: https://lore.kernel.org/43552d09-2ce2-4b19-b0d3-a2d1ab952145@I-love.SAKURA.ne.jp
Reported-by: syzbot+3f51ad7ac3ae57a6fdcc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3f51ad7ac3ae57a6fdcc
Reported-by: syzbot+47cf95ca1f9dcca872c8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=47cf95ca1f9dcca872c8
Reported-by: syzbot+8a173e13208949931dc7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8a173e13208949931dc7
Reported-by: syzbot+90984d3713722683112e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=90984d3713722683112e
Analyzed-by: AI Mode in Google Search (no mail address)
Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts")
Signed-off-by: Tetsuo Handa 
Reviewed-by: Alexander Potapenko 
Cc: Alan Stern 
Cc: Andrey Konovalov 
Cc: Christoph Hellwig 
Cc: Clark Williams 
Cc: Dmitry Vyukov 
Cc: Greg Kroah-Hartman 
Cc: Marco Elver 
Cc: Mark Brown 
Cc: Roman Gushchin 
Cc: Sebastian Andrzej Siewior 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Greg Kroah-Hartman

pid: reject allocations through dead ancestor pid namespaces

2026-08-23T12:29:33+00:00

[ Upstream commit b64a9f67e082e04835ddd69d422a25168d69375b ]

alloc_pid() checks PIDNS_ADDING only on the leaf pid namespace before
making a new struct pid visible in every ancestor namespace. That is
insufficient when an unborn descendant pid namespace outlives an
ancestor whose init task has already exited. The descendant can still be
initialized later through setns(), and the new pid is then published
into the dead ancestor as well.

Keep the existing ENOMEM behavior, but require PIDNS_ADDING to be set in
every namespace that will receive the new pid before publishing any of
them. This preserves the invariant that free_pid() never decrements
pid_allocated in a namespace whose child_reaper is no longer live.

Fixes: a3bdc23ba8ea ("pid_namespace: allow opening pid_for_children before init was created")
Signed-off-by: Jérémy Jean 
Reviewed-by: Pavel Tikhomirov 
Signed-off-by: Christian Brauner (Amutable) 
Signed-off-by: Sasha Levin

perf: Reject exited events as group leaders

2026-08-23T12:29:30+00:00

[ Upstream commit fa091f46c3833fb22384f10eade2b4e1e1d0b278 ]

perf_event_remove_on_exec() sets remove-on-exec events to the EXIT state
and detaches their group relationships.  The event's file descriptor can
remain open, however, and perf_event_open() currently accepts that event
as a group leader because its early validation rejects only REVOKED and
DEAD events.

A new sibling can consequently be linked to the detached leader.  When
the leader is closed, perf_group_detach() observes that its
PERF_ATTACH_GROUP bit is already clear and skips the new sibling.  The
sibling then retains a group_leader pointer to the freed event.

Reject group leaders in the EXIT state.  Perform the check while holding
the shared context mutex so that an exec in the target task cannot detach
the leader between validation and group attachment.

[peterz: make the earlier test fully consistent]
Fixes: 037a3c43edfb ("perf/core: Detach event groups during remove_on_exec")
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Kyle Zeng 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://patch.msgid.link/20260806205655.75722-1-kylebot@openai.com
Signed-off-by: Sasha Levin