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 E267A5505D0 for ; Tue, 22 Sep 2026 15:22:55 +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=1790090577; cv=none; b=kxf6lDAvvV7pNVrB28s0K0e5UvX0E1MmUEvfPu+g31fZ2ndAikZaL0k/uj0Nuy4Xoeay8TkfY2folhc8aqcJvH60ou9Szb2kID6do/F8dODyAPqHron+3PfX2E7pZraZFcEucRKh3e+SaT/F0H0VUJ7DewXw2ED6sLYY19JV8VI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790090577; c=relaxed/simple; bh=0zeXwD9zlx+gVGzZNs0rIeo/BYmpYoI7OcleeUXzwSk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=uEzFP7ozzC7WWDhuLZzAxCAqnBnX95tPdevJqrpf3OG4PDGe3COWY8Brhkp151vWYG1pvfUXazgdFGMS9PvjeqqoIdtzZPzo/acrgisQG4W34RsnqkNyLrmk/0hQwNNEJ6sI2nTMOX4yH6VFZtZbMtEVTvwJH3Ow1AaBpEZQBNI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bOjAbYWw; 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="bOjAbYWw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1395E1F000FF; Tue, 22 Sep 2026 15:22:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790090575; bh=cp4pvIg9n6ozNzoNEmJ9ZjmLHZ5bWE3Aqq+ZBAFY/0U=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bOjAbYWwOaXgfduMQMwuKHtj3VyLjsaN0lfUmhdlNWfbFipcgFk0bp0UjLqv+iWWc jPHbElN8Vg+ZY6KqzRzyoJ48sG7mRm76t1kXwhkxxDwzswM2S02Z7vcKibf2Lgi/3w sHTm5M7umb3QgqOr+MPoYAuhOVAG3WOEuo2OxFJrFMpHlQtrEm23ErVH63lcPNVsp3 hbbBLewY2om3/NVcTjPW9d7sk8qQA2Zw+KVeMvnRlPYUFxa733gL0jZG3qsTi0Luou psw2mTvm+Y2QvOSOWOVF2xLhtBGag+K4aCQTn5zjncSw9FOgBMb0yfNtrMPpuxvDBX uasMGuibZuZCw== From: Sasha Levin To: stable@vger.kernel.org Cc: Hyunwoo Kim , Thomas Gleixner , Kijo Park , Oleg Nesterov , Frederic Weisbecker , Sasha Levin Subject: [PATCH 6.1.y] exec: Cleanup POSIX timers right after de_thread() Date: Tue, 22 Sep 2026 11:22:53 -0400 Message-ID: <20260922152253.2800305-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026092225-humongous-ultimate-9930@gregkh> References: <2026092225-humongous-ultimate-9930@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Hyunwoo Kim [ Upstream commit acb03d3881818581052924a9bbbe92b8741ed448 ] 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 Tested-by: Kijo Park Reviewed-by: Oleg Nesterov Reviewed-by: Frederic Weisbecker Cc: stable@vger.kernel.org Link: https://patch.msgid.link/ao7Q8miiuLAPVnWv@v4bel Link: https://patch.msgid.link/20260911090541.627712075@kernel.org [ kept timer cleanup inline instead of introducing upstream’s posixtimer_exec() helper. ] Signed-off-by: Sasha Levin --- fs/exec.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index e4dd402aa4ce6..8e91240a71e17 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1268,6 +1268,21 @@ int begin_new_exec(struct linux_binprm * bprm) 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. + * Otherwise in case of a TID switch the deletion of the related POSIX + * timer would not remove an enqueued timer because the TID lookup + * of the old TID fails. + */ +#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 + /* * Cancel any io_uring activity across execve */ @@ -1302,14 +1317,6 @@ int begin_new_exec(struct linux_binprm * bprm) bprm->mm = NULL; -#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. */ -- 2.53.0