From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793209868; b=fZeH44ZO8WsXYXtjS+dwK9QAMZ2ILzhH9BM+SnRVAaL4mTLsmZ+D98EVCHMD3a09Nj/J E3RbDK9BIwAocC7RzV9Z/SkaJiJxrbxe5VqKoyOxwZvLQuqlOjQJOKcDqTJ0x9tS0eQLH Fmjm2U1ealvARrSGQAOaPN1r/pyRlVXWeUX6GdhJvpVyGQzMm+CZnIyNoRE2THgTXljom DU6LiHouCmTmvXxhVUnERXZENI9iiZroKK9wOE2lU8O8fwBZV+GRA/BjlnRGibSJzvqyH /hatP5L+SKDvqJk5rg/uplNaE52iyxYQFUA8DZummZDVZwsiK9o13TQzok8GL6m744g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793209868; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=hok726YB0IkF3IdYcsyrB3vjA2mR0WiMVZR1rgxuISs=; b=s4oSIQehJ6mcg7wgTN4rjWfFl1D5LHRwULGial6s2ldvFS2QdYGlcnKuO5RjLmYoIi4m Zkra0LXF7UB+ctBwr83sNzducQkm2UzR1dlME5pQV6KiMjDEYw37+xNTZNpNZWsMFal90 Dkqq9pjKKVotGfhQK5okwwXllvPyZGPaOMQZG9Duh++lT0hELpNPvvAbBBkwKQMYocPHV idH+IJwelkA8H1Pigcfy0/OSHOJ4IZWAqe9ZFCJUWxoIzEtSMW11jGNk5Tbm8IR02gbDp AG9JKxgL0Bgjj9RBWZfrbP7LzLNd4DOo1HqcconjJJn6ty6Khf/Wu7gQOzCVrYWxwKQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=moIAi+xO; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 62163606A31A; Wed, 28 Oct 2026 17:51:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=moIAi+xO Received: by smtp.kernel.org (Postfix) with ESMTPSA id AEFF71F01825; Wed, 28 Oct 2026 17:51:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793209868; bh=hok726YB0IkF3IdYcsyrB3vjA2mR0WiMVZR1rgxuISs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=moIAi+xOD4oqwiG5F5FbIb5DkNEwg6KNAfd7cMd/1ykGz2FTBpYENIx7iCNkNsSoa 2LGDIGJSzSv9CUHESkJ6B2R1GaS0deUwHFTFAhD/c7ujTxG36SH++GARrOx4u+6w++ FEVMUAz6Q4WQGP3JjbhH9wPtWaQ6yrMB/onoePU8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chris Mason , Oleg Nesterov , "Christian Brauner (Amutable)" Subject: [PATCH 6.18 106/109] exit: hang up the tty before closing the files Date: Wed, 28 Oct 2026 18:01:30 +0100 Message-ID: <20261028165944.851240476@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028165942.357251485@linuxfoundation.org> References: <20261028165942.357251485@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner commit ad016f0131ebfec250a3360ea75d35128b3f4aa8 upstream. do_exit() closes the task's files in exit_files() and hangs up the controlling tty of a session leader in disassociate_ctty(1) after that. Since commit d99d38540bf0 ("fs: make close_files() synchronous") the final __fput() of every file runs inside exit_files(). So when the session leader holds the last open of its tty the tty is released before disassociate_ctty() runs. tty_release() clears signal->tty for the whole session in session_clear_tty() once the count drops to zero and sends no signal doing so. disassociate_ctty(1) then finds neither a tty nor a tty_old_pgrp and does nothing. The foreground process group loses its SIGHUP: do_exit() exit_files() close_files() tty_release() tty->count == 0 session_clear_tty() signal->tty = NULL, no signal disassociate_ctty(1) get_current_tty() NULL signal->tty_old_pgrp NULL, nothing sent That only affects real ttys. For a pty the master's open keeps the slave's count above zero. And it only affects a foreground job that holds no descriptor to the tty anymore while its session leader exits. Everything else is unchanged. The DTR drop on the last close happens in tty_port_shutdown() regardless, stopped jobs get their SIGHUP from kill_orphaned_pgrp() and signal->tty is cleared either way. Before that commit the final __fput() ran from exit_task_work() which comes after disassociate_ctty(). That order isn't old. Until v3.14 exit_task_work() came right after exit_files() and before v3.6 fput() was synchronous, so the tty was always released first. Commit c39df5fa37b0 ("exit: call disassociate_ctty() before exit_task_namespaces()") moved disassociate_ctty() up to fix a pppd crash and in front of exit_task_work() as a side effect. The hangup in this case has worked since then and that's eleven years of userspace being able to rely on it. Hang the tty up before closing the files. This is the ordinary hangup with the file still open: __tty_hangup() swaps in hung_up_tty_fops and tty_release() runs from the close afterwards as it does when a modem drops the line. disassociate_ctty() stays in front of exit_task_namespaces() which the pppd fix needs. Reported-by: Chris Mason Link: https://patch.msgid.link/20260921-work-coredump-fixes-v3-8-8e4adb1619e6@kernel.org Acked-by: Oleg Nesterov Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- kernel/exit.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/kernel/exit.c +++ b/kernel/exit.c @@ -974,10 +974,11 @@ void __noreturn do_exit(long code) exit_sem(tsk); exit_shm(tsk); - exit_files(tsk); - exit_fs(tsk); + /* Hang the tty up before the last close of it can clear the session. */ if (group_dead) disassociate_ctty(1); + exit_files(tsk); + exit_fs(tsk); exit_nsproxy_namespaces(tsk); exit_task_work(tsk); exit_thread(tsk);