From owner-freebsd-bugs@freebsd.org Thu Dec 17 19:22:21 2020 Return-Path: Delivered-To: freebsd-bugs@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 54D8D4C1177 for ; Thu, 17 Dec 2020 19:22:21 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mailman.nyi.freebsd.org (mailman.nyi.freebsd.org [IPv6:2610:1c1:1:606c::50:13]) by mx1.freebsd.org (Postfix) with ESMTP id 4CxhhY1mWrz4dXP for ; Thu, 17 Dec 2020 19:22:21 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: by mailman.nyi.freebsd.org (Postfix) id 3CA184C1494; Thu, 17 Dec 2020 19:22:21 +0000 (UTC) Delivered-To: bugs@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 3C6944C1197 for ; Thu, 17 Dec 2020 19:22:21 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4CxhhY19Znz4d9t for ; Thu, 17 Dec 2020 19:22:21 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2610:1c1:1:606c::50:1d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 1BC851DE20 for ; Thu, 17 Dec 2020 19:22:21 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.5]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id 0BHJMKDP011539 for ; Thu, 17 Dec 2020 19:22:20 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id 0BHJMK1a011538 for bugs@FreeBSD.org; Thu, 17 Dec 2020 19:22:20 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 251915] TOCTOU race between tty_signal_sessleader() and killjobc() Date: Thu, 17 Dec 2020 19:22:20 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Some People X-Bugzilla-Who: kib@FreeBSD.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 17 Dec 2020 19:22:21 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D251915 --- Comment #5 from Konstantin Belousov --- (In reply to Jakub Piecuch from comment #4) You talked about a race with zeroing s_leader, but comment now mention t_session. I reformulated the comment, and also read t_session into local, just to shorten the lines and make this fragment easier to read. Also, atomics come from sys/systm.h already. diff --git a/sys/kern/tty.c b/sys/kern/tty.c index 7526638b921..8d4d25a4ac0 100644 --- a/sys/kern/tty.c +++ b/sys/kern/tty.c @@ -1474,6 +1474,7 @@ void tty_signal_sessleader(struct tty *tp, int sig) { struct proc *p; + struct session *s; tty_assert_locked(tp); MPASS(sig >=3D 1 && sig < NSIG); @@ -1482,8 +1483,14 @@ tty_signal_sessleader(struct tty *tp, int sig) tp->t_flags &=3D ~TF_STOPPED; tp->t_termios.c_lflag &=3D ~FLUSHO; - if (tp->t_session !=3D NULL && tp->t_session->s_leader !=3D NULL) { - p =3D tp->t_session->s_leader; + /* + * Load s_leader exactly once to avoid race where s_leader is + * set to NULL by a concurrent invocation of killjobc() by the + * session leader. Note that we are not holding t_session's + * lock for the read. + */ + if ((s =3D tp->t_session) !=3D NULL && + (p =3D atomic_load_ptr(&s->s_leader)) !=3D NULL) { PROC_LOCK(p); kern_psignal(p, sig); PROC_UNLOCK(p); --=20 You are receiving this mail because: You are the assignee for the bug.=