Date: Sun, 28 Jun 2026 00:30:02 +0000 From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: dc94d15a7136 - stable/14 - execve_block(): a mechanism for mutual exclusion with execve() on the process Message-ID: <6a406b0a.3f0b6.66555ae0@gitrepo.freebsd.org>
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The branch stable/14 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=dc94d15a7136c4cfe3342c005d8a319f0583ed9a commit dc94d15a7136c4cfe3342c005d8a319f0583ed9a Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2026-05-26 17:36:20 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2026-06-28 00:28:57 +0000 execve_block(): a mechanism for mutual exclusion with execve() on the process (cherry picked from commit e1a84b7708c2514769625c2af6c5034694013b6a) --- sys/kern/kern_exec.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++ sys/kern/kern_exit.c | 1 + sys/kern/kern_fork.c | 1 + sys/sys/imgact.h | 4 +++ sys/sys/proc.h | 3 ++ 5 files changed, 88 insertions(+) diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c index 349e13915b29..4461b9e4dc11 100644 --- a/sys/kern/kern_exec.c +++ b/sys/kern/kern_exec.c @@ -370,6 +370,77 @@ execve_nosetid(struct image_params *imgp) } } +/* + * Returns true if the execblock was obtained, in this case the + * process lock is kept. Returns false if the execblock was not + * obtained, but the function slept and the lock was dropped. + */ +bool +execve_block(struct thread *td, struct proc *p) +{ + PROC_LOCK_ASSERT(p, MA_OWNED); + MPASS(td == curthread); + MPASS(p != td->td_proc || (p->p_flag & P_INEXEC) == 0); + + if (p != td->td_proc && (p->p_flag & P_INEXEC) != 0) { + p->p_flag2 |= P2_INEXEC_WAIT; + msleep(&p->p_execblock, &p->p_mtx, PDROP, "inexec", 0); + return (false); + } + MPASS(p->p_execblock < UINT_MAX); + p->p_execblock++; + return (true); +} + +/* + * Might drop the process lock internally, callers must re-check the + * invariants afterward. + */ +void +execve_block_wait(struct thread *td, struct proc *p) +{ + bool first; + + PROC_ASSERT_HELD(p); + PROC_LOCK_ASSERT(p, MA_OWNED); + + for (first = true;; first = false) { + if (!first) + PROC_LOCK(p); + if (execve_block(td, p)) + return; + } +} + +void +execve_unblock(struct thread *td, struct proc *p) +{ + PROC_LOCK_ASSERT(p, MA_OWNED); + MPASS(td == curthread); + + MPASS(p->p_execblock > 0); + p->p_execblock--; + if (p->p_execblock == 0 && (p->p_flag2 & P2_INEXEC_WAIT) != 0) { + p->p_flag2 &= ~P2_INEXEC_WAIT; + wakeup(&p->p_execblock); + } +} + +void +execve_block_pass(struct thread *td) +{ + struct proc *p; + + MPASS(td == curthread); + p = td->td_proc; + PROC_LOCK_ASSERT(p, MA_OWNED); + + while (p->p_execblock != 0) { + p->p_flag2 |= P2_INEXEC_WAIT; + msleep(&p->p_execblock, &p->p_mtx, 0, "exeblk", 0); + } +} + /* * In-kernel implementation of execve(). All arguments are assumed to be * userspace pointers from the passed thread. @@ -425,6 +496,7 @@ do_execve(struct thread *td, struct image_args *args, struct mac *mac_p, PROC_LOCK(p); KASSERT((p->p_flag & P_INEXEC) == 0, ("%s(): process already has P_INEXEC flag", __func__)); + execve_block_pass(td); p->p_flag |= P_INEXEC; PROC_UNLOCK(p); @@ -893,7 +965,11 @@ interpret: * as we're now a bona fide freshly-execed process. */ KNOTE_LOCKED(p->p_klist, NOTE_EXEC); + MPASS(p->p_execblock == 0); + if ((p->p_flag2 & P2_INEXEC_WAIT) != 0) + wakeup(&p->p_execblock); p->p_flag &= ~P_INEXEC; + p->p_flag2 &= ~P2_INEXEC_WAIT; /* clear "fork but no exec" flag, as we _are_ execing */ p->p_acflag &= ~AFORK; @@ -975,7 +1051,10 @@ exec_fail_dealloc: exec_fail: /* we're done here, clear P_INEXEC */ PROC_LOCK(p); + if ((p->p_flag2 & P2_INEXEC_WAIT) != 0) + wakeup(&p->p_execblock); p->p_flag &= ~P_INEXEC; + p->p_flag2 &= ~P2_INEXEC_WAIT; PROC_UNLOCK(p); SDT_PROBE1(proc, , , exec__failure, error); diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c index bbd30dfb9480..baa5cad2bdc8 100644 --- a/sys/kern/kern_exit.c +++ b/sys/kern/kern_exit.c @@ -325,6 +325,7 @@ exit1(struct thread *td, int rval, int signo) while (p->p_lock > 0) msleep(&p->p_lock, &p->p_mtx, PWAIT, "exithold", 0); + MPASS(p->p_execblock == 0); PROC_UNLOCK(p); /* Drain the limit callout while we don't have the proc locked */ callout_drain(&p->p_limco); diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c index 7731ae4d14f3..d8578f01677b 100644 --- a/sys/kern/kern_fork.c +++ b/sys/kern/kern_fork.c @@ -384,6 +384,7 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread * bzero(&p2->p_startzero, __rangeof(struct proc, p_startzero, p_endzero)); + p2->p_execblock = 0; /* Tell the prison that we exist. */ prison_proc_hold(p2->p_ucred->cr_prison); diff --git a/sys/sys/imgact.h b/sys/sys/imgact.h index c1c94a2eabfd..d35f85620ac9 100644 --- a/sys/sys/imgact.h +++ b/sys/sys/imgact.h @@ -122,6 +122,10 @@ int exec_shell_imgact(struct image_params *); int exec_copyin_args(struct image_args *, const char *, char **, char **); int pre_execve(struct thread *td, struct vmspace **oldvmspace); void post_execve(struct thread *td, int error, struct vmspace *oldvmspace); +bool execve_block(struct thread *td, struct proc *p); +void execve_block_wait(struct thread *td, struct proc *p); +void execve_unblock(struct thread *td, struct proc *p); +void execve_block_pass(struct thread *td); #endif #endif /* !_SYS_IMGACT_H_ */ diff --git a/sys/sys/proc.h b/sys/sys/proc.h index 95a279742300..66b6a35c8d95 100644 --- a/sys/sys/proc.h +++ b/sys/sys/proc.h @@ -777,6 +777,7 @@ struct proc { TAILQ_HEAD(, kq_timer_cb_data) p_kqtim_stop; /* (c) */ LIST_ENTRY(proc) p_jaillist; /* (d) Jail process linkage. */ + u_int p_execblock; /* (c) Blockers for execve. */ }; #define p_session p_pgrp->pg_session @@ -890,6 +891,8 @@ struct proc { sync core registered */ #define P2_MEMBAR_GLOBE 0x00400000 /* membar global expedited registered */ +#define P2_INEXEC_WAIT 0x80000000 /* Not same as in HEAD. + Waiters for P_INEXEC/p_execblock */ /* Flags protected by proctree_lock, kept in p_treeflags. */ #define P_TREE_ORPHANED 0x00000001 /* Reparented, on orphan list */home | help
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