From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 216F63DEAC9 for ; Tue, 9 Jun 2026 21:02:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781038982; cv=none; b=JWQSFvYDWwWG8rF0IxujxAd8G0Bz7fwDJPjclDuLianRtBhVjEKJPVsOCQxDJtYB+na7JABdPTSl7GYrPkRwcoqBzunO1gcoFnWPj4OAZddRawFA1hkEkMnSpseiDN8Vl/aAdPxuqR3pcols87Fap98bVGcZxIMl683Zadfe/LE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781038982; c=relaxed/simple; bh=bQGZ3Gi1hecEzRonc8KkP4mUrFcfRliOT9dqTRLLRN4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ik1o/Cp1ySXsmjy+Jg/kppcT1tNXL9YNat9kLtd2lzIQrTY8RNOcfppEEVxwMl2NvxBVduvskWu+Ef8OKCx9BfUmSaqae38yhOuTWriaBJGkvTnKYwMg16hBR/WGjXxMnuqSJtpZoRHjTKnb6ABeFazg2+sfeqLY2fDP81vR24w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=Evfu3nvh; arc=none smtp.client-ip=198.175.65.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Evfu3nvh" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1781038977; x=1812574977; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=bQGZ3Gi1hecEzRonc8KkP4mUrFcfRliOT9dqTRLLRN4=; b=Evfu3nvhFQk62Z75UYE+kQZDQs6qC5atr6E55E1BJrLLf1LUi/RfsHrY QJNCcYDaoCuRqMeE1CKQzxCk/DCOIsWdbIIJVm+4Bc55lgNHa6Q6psSMs fAHmlaKf6kHkkwLp/7T02o30F9GAICvbMzw2VC8SkqplFe4iS1hbuz9b2 zaekRP9c833umwnA4cYLjoBw46Dkp9l5hNM5jnYYAmi+9YH8RgHp2yQWh BQdijdxLDFioGISk7Nu+4IJ0ZeeT2Cqz7VQna69GLItXu6sNR38iOLV3E 430M7erTOjNu9YXzvy6VkXH3Ayqi+qSZ2B5nZPc5ne8ljbcWBiy0h0HjY w==; X-CSE-ConnectionGUID: CMy+fcoRR2ebqMIt/VxmJw== X-CSE-MsgGUID: TXg6CjZqR5+xaMKD+ZIOug== X-IronPort-AV: E=McAfee;i="6800,10657,11812"; a="81885031" X-IronPort-AV: E=Sophos;i="6.24,196,1774335600"; d="scan'208";a="81885031" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by orvoesa110.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jun 2026 14:02:56 -0700 X-CSE-ConnectionGUID: rq9mlczNR2C0OTwo24NvLA== X-CSE-MsgGUID: JbXnfTi0STaH4dmC7jMfrg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,196,1774335600"; d="scan'208";a="251045719" Received: from rchatre-desk1.jf.intel.com ([10.165.154.99]) by fmviesa005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jun 2026 14:02:54 -0700 From: Reinette Chatre To: tony.luck@intel.com, james.morse@arm.com, Dave.Martin@arm.com, babu.moger@amd.com, bp@alien8.de, tglx@linutronix.de, dave.hansen@linux.intel.com Cc: x86@kernel.org, hpa@zytor.com, ben.horgan@arm.com, fustini@kernel.org, fenghuay@nvidia.com, peternewman@google.com, yu.c.chen@intel.com, linux-kernel@vger.kernel.org, patches@lists.linux.dev, reinette.chatre@intel.com Subject: [PATCH v5 07/11] fs/resctrl: Prevent use-after-free in rdtgroup_kn_put() Date: Tue, 9 Jun 2026 14:02:33 -0700 Message-ID: <9bfb3dc321d46b9d28d9952addc9c7e8a84437dc.1781029125.git.reinette.chatre@intel.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that need the structure to remain valid across a sleep (while waiting on acquiring rdtgroup_mutex) take a reference with rdtgroup_kn_get() and release it with rdtgroup_kn_put(). The release path is intended to serve as the fallback freer: if the count drops to zero and the group has already been marked RDT_DELETED, rdtgroup_kn_put() frees the structure. The bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub() resulting from a resctrl directory remove or resctrl fs unmount act as the primary freer: they hold rdtgroup_mutex and free each rdtgroup whose waitcount is zero, otherwise they set RDT_DELETED and leave the freeing to the last waiter. These two freers race. rdtgroup_kn_put() commits waitcount == 0 with atomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags. Between those two operations a concurrent caller of free_all_child_rdtgrp() or rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via atomic_read(), call rdtgroup_remove(), and kfree() the structure. The subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then a use-after-free, and the structure may even be freed twice if the freed memory happens to satisfy the RDT_DELETED flag check. Replace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock() so that the decrement-to-zero takes rdtgroup_mutex before the count becomes globally visible. The inspection of rdtgroup::flags then runs under the same mutex held by the bulk freers, making the two paths mutually exclusive. The common case where the count does not reach zero remains lock-free. Defer kernfs_unbreak_active_protection() until after the mutex is dropped since kernfs active protections functionally wrap rdtgroup_mutex. Remove resource group, which in turn drops its kernfs reference, after kernfs protection is restored. Fixes: b8511ccc75c0 ("x86/resctrl: Fix use-after-free when deleting resource groups") Reported-by: Sashiko Closes: https://sashiko.dev/#/patchset/20260515193944.15114-1-tony.luck%40intel.com?part=1 Assisted-by: GitHub_Copilot:gemini-3.1-pro Signed-off-by: Reinette Chatre Reviewed-by: Ben Horgan Reviewed-by: Tony Luck --- Changes since V2: - New patch Changes since V3: - Add Ben's Reviewed-by tag. - Add Tony's Reviewed-by tag. --- fs/resctrl/rdtgroup.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c index 0d073d4db734..c04424c081a4 100644 --- a/fs/resctrl/rdtgroup.c +++ b/fs/resctrl/rdtgroup.c @@ -2606,15 +2606,24 @@ static void rdtgroup_kn_get(struct rdtgroup *rdtgrp, struct kernfs_node *kn) static void rdtgroup_kn_put(struct rdtgroup *rdtgrp, struct kernfs_node *kn) { - if (atomic_dec_and_test(&rdtgrp->waitcount) && - (rdtgrp->flags & RDT_DELETED)) { + bool needs_free; + + if (!atomic_dec_and_mutex_lock(&rdtgrp->waitcount, &rdtgroup_mutex)) { + kernfs_unbreak_active_protection(kn); + return; + } + + needs_free = rdtgrp->flags & RDT_DELETED; + + mutex_unlock(&rdtgroup_mutex); + + kernfs_unbreak_active_protection(kn); + + if (needs_free) { if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP || rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) rdtgroup_pseudo_lock_remove(rdtgrp); - kernfs_unbreak_active_protection(kn); rdtgroup_remove(rdtgrp); - } else { - kernfs_unbreak_active_protection(kn); } } -- 2.50.1