Date: Thu, 27 May 2021 19:53:23 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: f3851b235b23 - main - ktrace: Fix a race with fork() Message-ID: <202105271953.14RJrN36017670@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=f3851b235b23d9220ace31bbc89b1fe0a78fc75c commit f3851b235b23d9220ace31bbc89b1fe0a78fc75c Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2021-05-27 19:49:59 +0000 Commit: Mark Johnston <markj@FreeBSD.org> 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)) { + /* + * 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); }
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