Date: Fri, 26 Jun 2026 22:20:44 +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: a80e40ce9ee0 - stable/15 - execve_block(): a mechanism for mutual exclusion with execve() on the process Message-ID: <6a3efb3c.272c8.a59c457@gitrepo.freebsd.org>
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The branch stable/15 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=a80e40ce9ee0a0641927730a193ff1f5641e71b6 commit a80e40ce9ee0a0641927730a193ff1f5641e71b6 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2026-05-26 17:36:20 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2026-06-26 22:16:03 +0000 execve_block(): a mechanism for mutual exclusion with execve() on the process (cherry picked from commit e1a84b7708c2514769625c2af6c5034694013b6a) --- sys/kern/kern_exec.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++-- sys/kern/kern_exit.c | 1 + sys/kern/kern_fork.c | 1 + sys/sys/imgact.h | 3 +++ sys/sys/proc.h | 3 ++- 5 files changed, 74 insertions(+), 3 deletions(-) diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c index e7552bab6005..ed7534af21bf 100644 --- a/sys/kern/kern_exec.c +++ b/sys/kern/kern_exec.c @@ -385,6 +385,62 @@ 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_flag |= P_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_flag & P_INEXEC_WAIT) != 0) { + p->p_flag &= ~P_INEXEC_WAIT; + wakeup(&p->p_execblock); + } +} + /* * In-kernel implementation of execve(). All arguments are assumed to be * userspace pointers from the passed thread. @@ -440,6 +496,10 @@ 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__)); + while (p->p_execblock != 0) { + p->p_flag |= P_INEXEC_WAIT; + msleep(&p->p_execblock, &p->p_mtx, 0, "exeblk", 0); + } p->p_flag |= P_INEXEC; PROC_UNLOCK(p); @@ -910,7 +970,10 @@ interpret: * as we're now a bona fide freshly-execed process. */ KNOTE_LOCKED(p->p_klist, NOTE_EXEC); - p->p_flag &= ~P_INEXEC; + MPASS(p->p_execblock == 0); + if ((p->p_flag & P_INEXEC_WAIT) != 0) + wakeup(&p->p_execblock); + p->p_flag &= ~(P_INEXEC | P_INEXEC_WAIT); /* clear "fork but no exec" flag, as we _are_ execing */ p->p_acflag &= ~AFORK; @@ -1006,7 +1069,9 @@ exec_fail_dealloc: exec_fail: /* we're done here, clear P_INEXEC */ PROC_LOCK(p); - p->p_flag &= ~P_INEXEC; + if ((p->p_flag & P_INEXEC_WAIT) != 0) + wakeup(&p->p_execblock); + p->p_flag &= ~(P_INEXEC | P_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 2f94386c9101..8f9007752b3b 100644 --- a/sys/kern/kern_exit.c +++ b/sys/kern/kern_exit.c @@ -365,6 +365,7 @@ 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 3de2a6224834..313fdef86fd8 100644 --- a/sys/kern/kern_fork.c +++ b/sys/kern/kern_fork.c @@ -431,6 +431,7 @@ 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 51cda4406cad..8c91b3a54bfa 100644 --- a/sys/sys/imgact.h +++ b/sys/sys/imgact.h @@ -123,6 +123,9 @@ 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); #endif #endif /* !_SYS_IMGACT_H_ */ diff --git a/sys/sys/proc.h b/sys/sys/proc.h index fd5c366ab95d..4e423c3ad0c7 100644 --- a/sys/sys/proc.h +++ b/sys/sys/proc.h @@ -780,6 +780,7 @@ struct proc { LIST_ENTRY(proc) p_jaillist; /* (d) Jail process linkage. */ u_int p_asig; /* (c) ASYNCEXIT pending signal. */ u_int p_tree_refcnt; /* (e) proctree refcount */ + u_int p_execblock; /* (c) Blockers for execve. */ }; #define p_session p_pgrp->pg_session @@ -852,7 +853,7 @@ struct proc { #define P_STATCHILD 0x08000000 /* Child process stopped or exited. */ #define P_INMEM 0x10000000 /* Loaded into memory, always set. */ #define P_ASYNC_EXIT 0x20000000 /* XXX */ -#define P_UNUSED2 0x40000000 /* --available-- */ +#define P_INEXEC_WAIT 0x40000000 /* Waiters for P_INEXEC/p_execblock */ #define P_PPTRACE 0x80000000 /* PT_TRACEME by vforked child. */ #define P_STOPPED (P_STOPPED_SIG|P_STOPPED_SINGLE|P_STOPPED_TRACE)home | help
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