Date: Fri, 19 Feb 2021 21:49:53 GMT From: Jamie Gritton <jamie@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: c837631bd47a - stable/11 - MFC jail: Handle a possible race between jail_remove(2) and fork(2) Message-ID: <202102192149.11JLnrxm040949@gitrepo.freebsd.org>
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The branch stable/11 has been updated by jamie: URL: https://cgit.FreeBSD.org/src/commit/?id=c837631bd47af73d03e3d8907f1e58b88403007c commit c837631bd47af73d03e3d8907f1e58b88403007c Author: Jamie Gritton <jamie@FreeBSD.org> AuthorDate: 2021-02-16 19:19:13 +0000 Commit: Jamie Gritton <jamie@FreeBSD.org> CommitDate: 2021-02-19 21:49:34 +0000 MFC jail: Handle a possible race between jail_remove(2) and fork(2) jail_remove(2) includes a loop that sends SIGKILL to all processes in a jail, but skips processes in PRS_NEW state. Thus it is possible the a process in mid-fork(2) during jail removal can survive the jail being removed. Add a prison flag PR_REMOVE, which is checked before the new process returns. If the jail is being removed, the process will then exit. Also check this flag in jail_attach(2) which has a similar issue. Reported by: trasz Approved by: kib (cherry picked from commit cc7b73065302005ebc4a19503188c8d6d5eb923d) --- sys/kern/kern_fork.c | 6 ++++++ sys/kern/kern_jail.c | 18 ++++++++++++++++++ sys/sys/jail.h | 1 + 3 files changed, 25 insertions(+) diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c index 2aa5f405d3c2..ea35afb42f99 100644 --- a/sys/kern/kern_fork.c +++ b/sys/kern/kern_fork.c @@ -1144,6 +1144,12 @@ fork_return(struct thread *td, struct trapframe *frame) PROC_UNLOCK(p); } + /* + * If the prison was killed mid-fork, die along with it. + */ + if (td->td_ucred->cr_prison->pr_flags & PR_REMOVE) + exit1(td, 0, SIGKILL); + userret(td, frame); #ifdef KTRACE diff --git a/sys/kern/kern_jail.c b/sys/kern/kern_jail.c index 47cc3ddd3bce..0bb9c76a25c9 100644 --- a/sys/kern/kern_jail.c +++ b/sys/kern/kern_jail.c @@ -1751,6 +1751,7 @@ kern_jail_set(struct thread *td, struct uio *optuio, int flags) } } pr->pr_flags = (pr->pr_flags & ~ch_flags) | pr_flags; + pr->pr_flags &= ~PR_REMOVE; mtx_unlock(&pr->pr_mtx); #ifdef RACCT @@ -2287,6 +2288,12 @@ prison_remove_one(struct prison *pr) struct proc *p; int deuref; + /* + * Mark the prison as doomed, so it doesn't accidentally come back + * to life. It may still be explicitly brought back by jail_set(2). + */ + pr->pr_flags |= PR_REMOVE; + /* If the prison was persistent, it is not anymore. */ deuref = 0; if (pr->pr_flags & PR_PERSIST) { @@ -2431,6 +2438,17 @@ do_jail_attach(struct thread *td, struct prison *pr) #endif prison_deref(oldcred->cr_prison, PD_DEREF | PD_DEUREF); crfree(oldcred); + + /* + * If the prison was killed while changing credentials, die along + * with it. + */ + if (pr->pr_flags & PR_REMOVE) { + PROC_LOCK(p); + kern_psignal(p, SIGKILL); + PROC_UNLOCK(p); + } + return (0); e_unlock: diff --git a/sys/sys/jail.h b/sys/sys/jail.h index 7142d0d0d71a..90a3fbce821f 100644 --- a/sys/sys/jail.h +++ b/sys/sys/jail.h @@ -209,6 +209,7 @@ struct prison_racct { /* primary jail address. */ /* Internal flag bits */ +#define PR_REMOVE 0x01000000 /* In process of being removed */ #define PR_IP4 0x02000000 /* IPv4 restricted or disabled */ /* by this jail or an ancestor */ #define PR_IP6 0x04000000 /* IPv6 restricted or disabled */
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