From b61b6f95d6722ddbbbd09e689fa41b55fd36f9a5 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 11 Sep 2026 11:04:47 +0200 Subject: [PATCH] futex: Also allocate private hash on vfork() As Jann demonstrated, it is entirely feasible to access the mm through vfork(). Therefore we need to allocate a private hash on vfork() as well as any other CLONE_VM user. Specifically, it must be avoided to have (private) futex waiters before allocating the private hash. Fixes: ee9dce44362b ("futex: Drop CLONE_THREAD requirement for private default hash alloc") Reported-by: Jann Horn Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260911090447.GT788244@noisy.programming.kicks-ass.net --- kernel/fork.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index a5934a317634..5ef413368912 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1996,9 +1996,9 @@ static bool need_futex_hash_allocate_default(u64 clone_flags) { /* * Allocate a default futex hash for any sibling that will - * share the parent's mm, except vfork. + * share the parent's mm. */ - return (clone_flags & (CLONE_VM | CLONE_VFORK)) == CLONE_VM; + return clone_flags & CLONE_VM; } /*