From owner-dev-commits-src-branches@freebsd.org Thu Dec 24 11:13:14 2020 Return-Path: Delivered-To: dev-commits-src-branches@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 C084E4C014D; Thu, 24 Dec 2020 11:13:14 +0000 (UTC) (envelope-from git@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 4D1nVy52VMz3ml3; Thu, 24 Dec 2020 11:13:14 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (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 9FBA079B4; Thu, 24 Dec 2020 11:13:14 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 0BOBDE53065988; Thu, 24 Dec 2020 11:13:14 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 0BOBDEs5065987; Thu, 24 Dec 2020 11:13:14 GMT (envelope-from git) Date: Thu, 24 Dec 2020 11:13:14 GMT Message-Id: <202012241113.0BOBDEs5065987@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org From: Konstantin Belousov Subject: git: 7688c099fc21 - MFC r368735: Fix a race in tty_signal_sessleader() with unlocked read of s_leader. MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: kib X-Git-Repository: src X-Git-Refname: refs/heads/stable/12 X-Git-Reftype: branch X-Git-Commit: 7688c099fc21d20fe0cf1bc3097b4a0ce5178753 Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-branches@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: "Commit messages for the stable branches of the src repository." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 24 Dec 2020 11:13:14 -0000 The branch stable/12 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=7688c099fc21d20fe0cf1bc3097b4a0ce5178753 commit 7688c099fc21d20fe0cf1bc3097b4a0ce5178753 Author: Konstantin Belousov AuthorDate: 2020-12-17 19:51:39 +0000 Commit: Konstantin Belousov CommitDate: 2020-12-24 10:56:35 +0000 MFC r368735: Fix a race in tty_signal_sessleader() with unlocked read of s_leader. (cherry picked from commit 551e205f6dfa469f4f32a166ee3fb691201d27a7) --- sys/kern/tty.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/sys/kern/tty.c b/sys/kern/tty.c index 3cd0262d6042..f82c1feca021 100644 --- a/sys/kern/tty.c +++ b/sys/kern/tty.c @@ -1462,6 +1462,7 @@ void tty_signal_sessleader(struct tty *tp, int sig) { struct proc *p; + struct session *s; tty_assert_locked(tp); MPASS(sig >= 1 && sig < NSIG); @@ -1469,8 +1470,14 @@ tty_signal_sessleader(struct tty *tp, int sig) /* Make signals start output again. */ tp->t_flags &= ~TF_STOPPED; - if (tp->t_session != NULL && tp->t_session->s_leader != NULL) { - p = 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 = tp->t_session) != NULL && + (p = atomic_load_ptr(&s->s_leader)) != NULL) { PROC_LOCK(p); kern_psignal(p, sig); PROC_UNLOCK(p);