From owner-dev-commits-src-main@freebsd.org Tue Jun 1 12:44:38 2021 Return-Path: Delivered-To: dev-commits-src-main@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 D25B5653BFC; Tue, 1 Jun 2021 12:44:38 +0000 (UTC) (envelope-from dchagin@heemeyer.club) Received: from heemeyer.club (heemeyer.club [IPv6:2001:19f0:6400:80a1:5054:ff:fe7a:a27d]) (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 mx1.freebsd.org (Postfix) with ESMTPS id 4FvX116Z51z3BsR; Tue, 1 Jun 2021 12:44:37 +0000 (UTC) (envelope-from dchagin@heemeyer.club) Received: from heemeyer.club (localhost [127.0.0.1]) by heemeyer.club (8.16.1/8.16.1) with ESMTP id 151CiUaZ001621; Tue, 1 Jun 2021 12:44:30 GMT (envelope-from dchagin@heemeyer.club) Received: (from dchagin@localhost) by heemeyer.club (8.16.1/8.16.1/Submit) id 151CiU7V001620; Tue, 1 Jun 2021 12:44:30 GMT (envelope-from dchagin) Date: Tue, 1 Jun 2021 12:44:30 +0000 From: Dmitry Chagin To: Mark Johnston Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: f3851b235b23 - main - ktrace: Fix a race with fork() Message-ID: References: <202105271953.14RJrN36017670@gitrepo.freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202105271953.14RJrN36017670@gitrepo.freebsd.org> X-Rspamd-Queue-Id: 4FvX116Z51z3BsR X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=none (mx1.freebsd.org: domain of dchagin@heemeyer.club has no SPF policy when checking 2001:19f0:6400:80a1:5054:ff:fe7a:a27d) smtp.mailfrom=dchagin@heemeyer.club X-Spamd-Result: default: False [-1.80 / 15.00]; RCVD_TLS_LAST(0.00)[]; ARC_NA(0.00)[]; FREEFALL_USER(0.00)[dchagin]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[freebsd.org]; RBL_DBL_DONT_QUERY_IPS(0.00)[2001:19f0:6400:80a1:5054:ff:fe7a:a27d:from]; AUTH_NA(1.00)[]; SPAMHAUS_ZRD(0.00)[2001:19f0:6400:80a1:5054:ff:fe7a:a27d:from:127.0.2.255]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-1.00)[-1.000]; R_SPF_NA(0.00)[no SPF record]; FORGED_SENDER(0.30)[dchagin@freebsd.org,dchagin@heemeyer.club]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:20473, ipnet:2001:19f0:6400::/38, country:US]; FROM_NEQ_ENVFROM(0.00)[dchagin@freebsd.org,dchagin@heemeyer.club]; MAILMAN_DEST(0.00)[dev-commits-src-all,dev-commits-src-main]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: dev-commits-src-main@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commit messages for the main branch of the src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 01 Jun 2021 12:44:38 -0000 On Thu, May 27, 2021 at 07:53:23PM +0000, Mark Johnston wrote: > The branch main has been updated by markj: > > URL: https://cgit.FreeBSD.org/src/commit/?id=f3851b235b23d9220ace31bbc89b1fe0a78fc75c > > commit f3851b235b23d9220ace31bbc89b1fe0a78fc75c > Author: Mark Johnston > AuthorDate: 2021-05-27 19:49:59 +0000 > Commit: Mark Johnston > CommitDate: 2021-05-27 19:52:20 +0000 > > ktrace: Fix a race with fork() > > ktrace(2) may toggle trace points in any of > 1. a single process > 2. all members of a process group > 3. all descendents of the processes in 1 or 2 > > In the first two cases, we do not permit the operation if the process is > being forked or not visible. However, in case 3 we did not enforce this > restriction for descendents. As a result, the assertions about the child > in ktrprocfork() may be violated. > > Move these checks into ktrops() so that they are applied consistently. > > Allow KTROP_CLEAR for nascent processes. Otherwise, there is a window > where we cannot clear trace points for a nascent child if they are > inherited from the parent. > > Reported by: syzbot+d96676592978f137e05c@syzkaller.appspotmail.com > Reported by: syzbot+7c98fcf84a4439f2817f@syzkaller.appspotmail.com > Reviewed by: kib > MFC after: 1 week > Sponsored by: The FreeBSD Foundation > Differential Revision: https://reviews.freebsd.org/D30481 > --- > sys/kern/kern_ktrace.c | 43 ++++++++++++++++++++++--------------------- > 1 file changed, 22 insertions(+), 21 deletions(-) > > diff --git a/sys/kern/kern_ktrace.c b/sys/kern/kern_ktrace.c > index dc064d9ebd67..4a2dad20b035 100644 > --- a/sys/kern/kern_ktrace.c > +++ b/sys/kern/kern_ktrace.c > @@ -1006,7 +1006,7 @@ sys_ktrace(struct thread *td, struct ktrace_args *uap) > int facs = uap->facs & ~KTRFAC_ROOT; > int ops = KTROP(uap->ops); > int descend = uap->ops & KTRFLAG_DESCEND; > - int nfound, ret = 0; > + int ret = 0; > int flags, error = 0; > struct nameidata nd; > struct ktr_io_params *kiop, *old_kiop; > @@ -1080,42 +1080,31 @@ restart: > error = ESRCH; > goto done; > } > + > /* > * ktrops() may call vrele(). Lock pg_members > * by the proctree_lock rather than pg_mtx. > */ > PGRP_UNLOCK(pg); > - nfound = 0; > + if (LIST_EMPTY(&pg->pg_members)) { > + sx_sunlock(&proctree_lock); > + error = ESRCH; > + goto done; > + } > LIST_FOREACH(p, &pg->pg_members, p_pglist) { > PROC_LOCK(p); > - if (p->p_state == PRS_NEW || > - p_cansee(td, p) != 0) { > - PROC_UNLOCK(p); > - continue; > - } > - nfound++; > if (descend) > ret |= ktrsetchildren(td, p, ops, facs, kiop); > else > ret |= ktrops(td, p, ops, facs, kiop); > } > - if (nfound == 0) { > - sx_sunlock(&proctree_lock); > - error = ESRCH; > - goto done; > - } > } else { > /* > * by pid > */ > p = pfind(uap->pid); > - if (p == NULL) > + if (p == NULL) { > error = ESRCH; > - else > - error = p_cansee(td, p); > - if (error) { > - if (p != NULL) > - PROC_UNLOCK(p); > sx_sunlock(&proctree_lock); > goto done; > } > @@ -1187,8 +1176,20 @@ ktrops(struct thread *td, struct proc *p, int ops, int facs, > PROC_UNLOCK(p); > return (0); > } > - if (p->p_flag & P_WEXIT) { > - /* If the process is exiting, just ignore it. */ > + if ((ops == KTROP_SET && p->p_state == PRS_NEW) || !p_cansee(td, p)) { ^^^^^^^^^^^^^^ seems that it broke ktrace: root@mordor:~ # ktrace ls ktrace: ktrace.out: Operation not permitted > + /* > + * Disallow setting trace points if the process is being born. > + * This avoids races with trace point inheritance in > + * ktrprocfork(). > + */ > + PROC_UNLOCK(p); > + return (0); > + } > + if ((p->p_flag & P_WEXIT) != 0) { > + /* > + * There's nothing to do if the process is exiting, but avoid > + * signaling an error. > + */ > PROC_UNLOCK(p); > return (1); > }