From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DBCA44734CF; Fri, 4 Sep 2026 11:22:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788520951; cv=none; b=fjm63Yq5Bdb8xWoBL7ma+7ywhNHIKRCzBhirOzDMITeDmc4w8gu7btiKo8uiUsCFg3sJ1b/fZocD0NxegtDcY2xPAxWpSalGXL9qgIL0E3V72xSEk2efx3eNGn6+tI4byPxb+U6iEOroV4L6BsO4vTkBvdfFMr1MhTzVRAeFPeU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788520951; c=relaxed/simple; bh=c6LKdjCRtX9r7BkpBqhHl3YDIF7wMKwHPOCCdDBstSs=; h=Date:Message-ID:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=hpPD3zvrFULw6lFUpUdTZ17cdnwXw8bSYdJp30AZ6n7iGwUZEtxDpQU2LFK4w9u3jwBEO3lobgQx1XPtnhpzKiHUFvGqm42c0DbM75qmYZlez7ediQRwKHHcOBOlQH0ibrgSbbosxRKM8oN5Vnmh6j57KBDoR4pvhXHQ+1Bf32Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hBnkU74I; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hBnkU74I" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B98361F00A3E; Fri, 4 Sep 2026 11:22:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788520949; bh=/MjvIu2eMcDyB476Ez37rVlvnO35eZxH5+YssIQfLa8=; h=Date:From:To:Cc:Subject:References; b=hBnkU74I3TP8Z6ELqV8PmhBwn3sZ+74wmbRjNTGlhsCzAV9686nKBr2wqOa8wAbSr 5As/v5CNR1vokggX3aPjFYZRwNAL++foP23zxITyNuTDqmttVFGiT+F3pEt5f/feVz izDRxechzOORanTN0YK6euKRx52zGjYIGnjyHcKo5Ri/QY1T3sUgWH07BV9VSdmDve ucxXZSaVtQH/Lp6+datI+UCZVWdlP6Ye794dEhQWKOnRAlHWTRuTbnA3geeurDXt2u cdtsVVg/bvdFK8dChV/Tw4zwgJao85UFhiBqwIjr/3C7Rhe7FirBGBFV0ZHoGpG0io Qk6pAGlfC3dWw== Date: Fri, 04 Sep 2026 13:22:26 +0200 Message-ID: <20260904112202.131242426@kernel.org> User-Agent: quilt/0.69 From: Thomas Gleixner To: LKML Cc: Hyunwoo Kim , Oleg Nesterov , Frederic Weisbecker , Christian Brauner , Peter Zijlstra , John Stultz , Ingo Molnar , Alexander Viro , "Eric W. Biederman" , stable@vger.kernel.org Subject: [patch 2/8] exec: Cleanup POSIX timers right after de_thread() References: <20260904112100.683893401@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Hyunwoo Kim A per-thread CPU timer holds a reference to the PID of the thread it is attached to and, while it is armed, its node is queued in that thread's posix_cputimers. The task is looked up by that PID. When a non-leader thread exec()s, de_thread() changes which task owns that PID. pid_task(timer->it.cpu.pid, PIDTYPE_PID) then returns NULL, but the node is still queued on tsk, which is alive. timer_lock_sighand() takes a failed lookup to mean that the node is already dequeued, so it has nothing to undo. begin_new_exec() calls posix_cpu_timers_exit(me) right after exec_task_namespaces() and that removes the leftover node, so the state normally stays invisible. But bprm->point_of_no_return is set before de_thread(), so if unshare_files(), set_mm_exe_file(), exec_mmap() or exec_task_namespaces() fails, the task dies before it gets there. exit_itimers() then frees the k_itimer while its node is still queued, and reaping tsk later erases that freed node from the rbtree. In short: the non-leader thread B the parent timer_create(CLOCK_THREAD_CPUTIME_ID) timer_settime() arm_timer() // the node is queued on B execve() de_thread(B) exchange_tids(B, leader) // B's PID now belongs to the leader release_task(leader) __exit_signal(leader) posix_cpu_timers_exit(leader) // cleans leader's queue, not B's __unhash_process(leader) // that PID has no task anymore exec_mmap() mmap_read_lock_killable(old_mm) kill(B, SIGKILL) // -EINTR get_signal() do_exit() exit_itimers() posix_timer_delete() posix_cpu_timer_del() posix_timer_unhash_and_free() // freed while still queued wait4() release_task(B) posix_cpu_timers_exit(B) cleanup_timerqueue() timerqueue_del() // use-after-free Move the POSIX timer cleanup right after de_thread() before any of the later failure conditions brings the task into do_exit(). [ tglx: Move the cleanup right after de_thread() ] Fixes: 55e8c8eb2c7b ("posix-cpu-timers: Store a reference to a pid not a task") Signed-off-by: Hyunwoo Kim Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://patch.msgid.link/ao7Q8miiuLAPVnWv@v4bel --- Changes in v3: Move the cleanup right after de_thread() - Oleg Rework change log Changes in v2: - Add the trigger sequence and the KASAN log to the commit message. - v1: https://lore.kernel.org/all/anfgrsPlUdwBhdrp@v4bel/ --- fs/exec.c | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-) --- a/fs/exec.c +++ b/fs/exec.c @@ -1115,6 +1115,17 @@ static struct file *bprm_identity_file(c return bprm->file; } +static void posixtimer_exec(struct task_struct *me) +{ +#ifdef CONFIG_POSIX_TIMERS + spin_lock_irq(&me->sighand->siglock); + posix_cpu_timers_exit(me); + spin_unlock_irq(&me->sighand->siglock); + exit_itimers(me); + flush_itimer_signals(); +#endif +} + /* * Calling this is the point of no return. None of the failures will be * seen by userspace since either the process is already taking a fatal @@ -1152,6 +1163,16 @@ int begin_new_exec(struct linux_binprm * retval = de_thread(me); if (retval) goto out; + + /* + * This must be done here to ensure that POSIX CPU timers which were + * armed on the current task are dequeued from me::posix_cputimers. + * That ensures that in case of a TID switch the deletion of the related + * POSIX timer will not free an enqueued timer because the TID lookup + * failed as the original target TID was the old leader. + */ + posixtimer_exec(me); + /* see the comment in check_unsafe_exec() */ current->fs->in_exec = 0; /* @@ -1192,14 +1213,6 @@ int begin_new_exec(struct linux_binprm * if (retval) goto out_unlock; -#ifdef CONFIG_POSIX_TIMERS - spin_lock_irq(&me->sighand->siglock); - posix_cpu_timers_exit(me); - spin_unlock_irq(&me->sighand->siglock); - exit_itimers(me); - flush_itimer_signals(); -#endif - /* * Make the signal table private. */