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=1793216635; b=Fbqon9klkA+CjNhBqYVOLp7bdB6AnoKq2XHG5vwUne3BFo0iS3m9eY6+o3Jk2H42vgN7 BEVn9NHgOlnDJCh52zD4WPwf+nrenJNF09wpZx8iPHGBtmC1BTDRNBEaPICXFoUuhopz4 nd2Uo5nEQ8OT8wSWbB7xxYpPgRYonf17+4HFC3kTKXmh0ZQSrb6FuFwJAGdeX2csvv+Ys wjvqE2RGRyIgU9z0lPRqsyBrYyK2AM2g+3ZFLj0B79nVr5URWhowoyF7d78mCheLPEu3z /88IZh/vc5RNyCr7RUqn4K6UW53q6dCM9sCeme+kyZETwMCTVYcncrf0HztjYRRrOpw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793216635; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=IMzawOVSemx/cygt8hWtvNdg9Waa1LAl7gzh3vgtl2Y=; b=t0DxBsjeIYM/twalE6uTA7SWIvkULGLVTMFz1ZpdyFKTF2jJPWzZnQsMBj8kGvOHK8KN MU3pyxgJet9mSe414PHRDvoGEehCsNpcSol0Ysk5xdR+Hh+qQaUyYcrXlSXYm7kTZRgsV 2hlu7YzgF55rxFyqBunqVPwSnX//Neewdx3q4XfF7qdwzyiLRkTNHl6Je8fgrtYRGB758 5e4OLdQPOGukimb+t2cccgyqGURQv5CUpLeVDAvzqZtIUzqt8f3uv/LKMPrR81X70Aqe0 JARaqHbGhwMLeCNr5Oam+YRLdJfnbzNs9ZLAKoP1N/gcj6SxSzefPMnfZ1kaot68lzg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=hmNmx29k; 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 C9A1C606A31C for ; Wed, 28 Oct 2026 19:43:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=hmNmx29k Received: by smtp.kernel.org (Postfix) with ESMTPSA id 056881F01828; Wed, 28 Oct 2026 19:43:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793216634; bh=IMzawOVSemx/cygt8hWtvNdg9Waa1LAl7gzh3vgtl2Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=hmNmx29kMOUNfd3lZfD9dScay/YXgwZAaTcIE9Q73pl2XLTkw12bAg7H09IG682vj c2zGINbGNFbPkjM9UcRdHj5F7uUxp6fvURBIf1vZ4GHtyJ5VuaUz+uNeMU3NucRgvK gselJIUSUktBHIkyBJuEOGlPkQpqBjBPhOnVxjQGKW+zVh+v40UnCaNjVkWVSYA8Za smJvpeKgnJ/9FwCqiAxmsAX2PouM5F5sMxt1mKV2R3IlZtfHN5AM1XaWgMSXcrqhN/ RpVR+DfEhBWxrExyJuUIQvmbD6wGhbD7jFatup6+AcdK3A/0ECsuBoXCmZJ7b0hOKc hcfbBTiUiS/vg== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Chris Mason , Oleg Nesterov , Sasha Levin Subject: [PATCH 6.6.y] exit: hang up the tty before closing the files Date: Wed, 28 Oct 2026 15:43:52 -0400 Message-ID: <20261028194316.2073000-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026102827-compress-dance-a28e@gregkh> References: <2026102827-compress-dance-a28e@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit ad016f0131ebfec250a3360ea75d35128b3f4aa8 ] 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) [ sashal: adjusted context for exit_task_namespaces() instead of exit_nsproxy_namespaces() ] Signed-off-by: Sasha Levin --- kernel/exit.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index e2dae48578d96..97b0dc8c05558 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -882,10 +882,11 @@ 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_task_namespaces(tsk); exit_task_work(tsk); exit_thread(tsk); -- 2.53.0